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GNU C provides several language features not found in ISO standard C.
(The `-pedantic' option directs GCC to print a warning message if
any of these features is used.) To test for the availability of these
features in conditional compilation, check for a predefined macro
__GNUC__, which is always defined under GCC.
These extensions are available in C and Objective-C. Most of them are also available in C++. See section Extensions to the C++ Language, for extensions that apply only to C++.
Some features that are in ISO C99 but not C89 or C++ are also, as extensions, accepted by GCC in C89 mode and in C++.
(With them you can define "built-in" functions.)
5.1 Statements and Declarations in Expressions Putting statements and declarations inside expressions. 5.2 Locally Declared Labels Labels local to a statement-expression. 5.3 Labels as Values Getting pointers to labels, and computed gotos. 5.4 Nested Functions As in Algol and Pascal, lexical scoping of functions. 5.5 Constructing Function Calls Dispatching a call to another function. 5.6 Referring to a Type with typeoftypeof: referring to the type of an expression.5.7 Generalized Lvalues Using `?:', `,' and casts in lvalues. 5.8 Conditionals with Omitted Operands Omitting the middle operand of a `?:' expression. 5.9 Double-Word Integers Double-word integers--- long long int.5.10 Complex Numbers Data types for complex numbers. 5.11 Hex Floats Hexadecimal floating-point constants. 5.12 Arrays of Length Zero Zero-length arrays. 5.14 Arrays of Variable Length Arrays whose length is computed at run time. 5.13 Structures With No Members Structures with no members. 5.15 Macros with a Variable Number of Arguments. Macros with a variable number of arguments. 5.16 Slightly Looser Rules for Escaped Newlines Slightly looser rules for escaped newlines. 5.17 Non-Lvalue Arrays May Have Subscripts Any array can be subscripted, even if not an lvalue. 5.18 Arithmetic on void- and Function-PointersArithmetic on void-pointers and function pointers.5.19 Non-Constant Initializers Non-constant initializers. 5.20 Compound Literals Compound literals give structures, unions or arrays as values. 5.21 Designated Initializers Labeling elements of initializers. 5.23 Cast to a Union Type Casting to union type from any member of the union. 5.22 Case Ranges `case 1 ... 9' and such. 5.24 Mixed Declarations and Code Mixing declarations and code. 5.25 Declaring Attributes of Functions Declaring that functions have no side effects, or that they can never return. 5.26 Attribute Syntax Formal syntax for attributes. 5.27 Prototypes and Old-Style Function Definitions Prototype declarations and old-style definitions. 5.28 C++ Style Comments C++ comments are recognized. 5.29 Dollar Signs in Identifier Names Dollar sign is allowed in identifiers. 5.30 The Character ESC in Constants `\e' stands for the character ESC. 5.32 Specifying Attributes of Variables Specifying attributes of variables. 5.33 Specifying Attributes of Types Specifying attributes of types. 5.31 Inquiring on Alignment of Types or Variables Inquiring about the alignment of a type or variable. 5.34 An Inline Function is As Fast As a Macro Defining inline functions (as fast as macros). 5.35 Assembler Instructions with C Expression Operands Assembler instructions with C expressions as operands.
5.36 Constraints for asmOperandsConstraints for asm operands 5.37 Controlling Names Used in Assembler Code Specifying the assembler name to use for a C symbol. 5.38 Variables in Specified Registers Defining variables residing in specified registers. 5.39 Alternate Keywords __const__,__asm__, etc., for header files.5.40 Incomplete enumTypesenum foo;, with details to follow.5.41 Function Names as Strings Printable strings which are the name of the current function. 5.42 Getting the Return or Frame Address of a Function Getting the return or frame address of a function. 5.43 Using vector instructions through built-in functions 5.44 Other built-in functions provided by GCC Other built-in functions. 5.45 Built-in Functions Specific to Particular Target Machines Built-in functions specific to particular targets. 5.46 Pragmas Accepted by GCC Pragmas accepted by GCC. 5.47 Unnamed struct/union fields within structs/unions. 5.48 Thread-Local Storage Per-thread variables.
A compound statement enclosed in parentheses may appear as an expression in GNU C. This allows you to use loops, switches, and local variables within an expression.
Recall that a compound statement is a sequence of statements surrounded by braces; in this construct, parentheses go around the braces. For example:
({ int y = foo (); int z;
if (y > 0) z = y;
else z = - y;
z; })
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is a valid (though slightly more complex than necessary) expression
for the absolute value of foo ().
The last thing in the compound statement should be an expression
followed by a semicolon; the value of this subexpression serves as the
value of the entire construct. (If you use some other kind of statement
last within the braces, the construct has type void, and thus
effectively no value.)
This feature is especially useful in making macro definitions "safe" (so that they evaluate each operand exactly once). For example, the "maximum" function is commonly defined as a macro in standard C as follows:
#define max(a,b) ((a) > (b) ? (a) : (b)) |
But this definition computes either a or b twice, with bad
results if the operand has side effects. In GNU C, if you know the
type of the operands (here let's assume int), you can define
the macro safely as follows:
#define maxint(a,b) \
({int _a = (a), _b = (b); _a > _b ? _a : _b; })
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Embedded statements are not allowed in constant expressions, such as the value of an enumeration constant, the width of a bit-field, or the initial value of a static variable.
If you don't know the type of the operand, you can still do this, but you
must use typeof (see section 5.6 Referring to a Type with typeof).
Statement expressions are not supported fully in G++, and their fate there is unclear. (It is possible that they will become fully supported at some point, or that they will be deprecated, or that the bugs that are present will continue to exist indefinitely.) Presently, statement expressions do not work well as default arguments.
In addition, there are semantic issues with statement-expressions in C++. If you try to use statement-expressions instead of inline functions in C++, you may be surprised at the way object destruction is handled. For example:
#define foo(a) ({int b = (a); b + 3; })
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does not work the same way as:
inline int foo(int a) { int b = a; return b + 3; }
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In particular, if the expression passed into foo involves the
creation of temporaries, the destructors for those temporaries will be
run earlier in the case of the macro than in the case of the function.
These considerations mean that it is probably a bad idea to use statement-expressions of this form in header files that are designed to work with C++. (Note that some versions of the GNU C Library contained header files using statement-expression that lead to precisely this bug.)
Each statement expression is a scope in which local labels can be
declared. A local label is simply an identifier; you can jump to it
with an ordinary goto statement, but only from within the
statement expression it belongs to.
A local label declaration looks like this:
__label__ label; |
or
__label__ label1, label2, /* ... */; |
Local label declarations must come at the beginning of the statement expression, right after the `({', before any ordinary declarations.
The label declaration defines the label name, but does not define
the label itself. You must do this in the usual way, with
label:, within the statements of the statement expression.
The local label feature is useful because statement expressions are
often used in macros. If the macro contains nested loops, a goto
can be useful for breaking out of them. However, an ordinary label
whose scope is the whole function cannot be used: if the macro can be
expanded several times in one function, the label will be multiply
defined in that function. A local label avoids this problem. For
example:
#define SEARCH(array, target) \
({ \
__label__ found; \
typeof (target) _SEARCH_target = (target); \
typeof (*(array)) *_SEARCH_array = (array); \
int i, j; \
int value; \
for (i = 0; i < max; i++) \
for (j = 0; j < max; j++) \
if (_SEARCH_array[i][j] == _SEARCH_target) \
{ value = i; goto found; } \
value = -1; \
found: \
value; \
})
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You can get the address of a label defined in the current function
(or a containing function) with the unary operator `&&'. The
value has type void *. This value is a constant and can be used
wherever a constant of that type is valid. For example:
void *ptr; /* ... */ ptr = &&foo; |
To use these values, you need to be able to jump to one. This is done
with the computed goto statement(3), goto *exp;. For example,
goto *ptr; |
Any expression of type void * is allowed.
One way of using these constants is in initializing a static array that will serve as a jump table:
static void *array[] = { &&foo, &&bar, &&hack };
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Then you can select a label with indexing, like this:
goto *array[i]; |
Note that this does not check whether the subscript is in bounds--array indexing in C never does that.
Such an array of label values serves a purpose much like that of the
switch statement. The switch statement is cleaner, so
use that rather than an array unless the problem does not fit a
switch statement very well.
Another use of label values is in an interpreter for threaded code. The labels within the interpreter function can be stored in the threaded code for super-fast dispatching.
You may not use this mechanism to jump to code in a different function. If you do that, totally unpredictable things will happen. The best way to avoid this is to store the label address only in automatic variables and never pass it as an argument.
An alternate way to write the above example is
static const int array[] = { &&foo - &&foo, &&bar - &&foo,
&&hack - &&foo };
goto *(&&foo + array[i]);
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This is more friendly to code living in shared libraries, as it reduces the number of dynamic relocations that are needed, and by consequence, allows the data to be read-only.
A nested function is a function defined inside another function.
(Nested functions are not supported for GNU C++.) The nested function's
name is local to the block where it is defined. For example, here we
define a nested function named square, and call it twice:
foo (double a, double b)
{
double square (double z) { return z * z; }
return square (a) + square (b);
}
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The nested function can access all the variables of the containing
function that are visible at the point of its definition. This is
called lexical scoping. For example, here we show a nested
function which uses an inherited variable named offset:
bar (int *array, int offset, int size)
{
int access (int *array, int index)
{ return array[index + offset]; }
int i;
/* ... */
for (i = 0; i < size; i++)
/* ... */ access (array, i) /* ... */
}
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Nested function definitions are permitted within functions in the places where variable definitions are allowed; that is, in any block, before the first statement in the block.
It is possible to call the nested function from outside the scope of its name by storing its address or passing the address to another function:
hack (int *array, int size)
{
void store (int index, int value)
{ array[index] = value; }
intermediate (store, size);
}
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Here, the function intermediate receives the address of
store as an argument. If intermediate calls store,
the arguments given to store are used to store into array.
But this technique works only so long as the containing function
(hack, in this example) does not exit.
If you try to call the nested function through its address after the containing function has exited, all hell will break loose. If you try to call it after a containing scope level has exited, and if it refers to some of the variables that are no longer in scope, you may be lucky, but it's not wise to take the risk. If, however, the nested function does not refer to anything that has gone out of scope, you should be safe.
GCC implements taking the address of a nested function using a technique called trampolines. A paper describing them is available as
http://people.debian.org/~aaronl/Usenix88-lexic.pdf.
A nested function can jump to a label inherited from a containing
function, provided the label was explicitly declared in the containing
function (see section 5.2 Locally Declared Labels). Such a jump returns instantly to the
containing function, exiting the nested function which did the
goto and any intermediate functions as well. Here is an example:
bar (int *array, int offset, int size)
{
__label__ failure;
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
int i;
/* ... */
for (i = 0; i < size; i++)
/* ... */ access (array, i) /* ... */
/* ... */
return 0;
/* Control comes here from |
A nested function always has internal linkage. Declaring one with
extern is erroneous. If you need to declare the nested function
before its definition, use auto (which is otherwise meaningless
for function declarations).
bar (int *array, int offset, int size)
{
__label__ failure;
auto int access (int *, int);
/* ... */
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
/* ... */
}
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Using the built-in functions described below, you can record the arguments a function received, and call another function with the same arguments, without knowing the number or types of the arguments.
You can also record the return value of that function call, and later return that value, without knowing what data type the function tried to return (as long as your caller expects that data type).
The function saves the arg pointer register, structure value address, and all registers that might be used to pass arguments to a function into a block of memory allocated on the stack. Then it returns the address of that block.
The value of arguments should be the value returned by
__builtin_apply_args. The argument size specifies the size
of the stack argument data, in bytes.
This function returns a pointer to data describing how to return whatever value was returned by function. The data is saved in a block of memory allocated on the stack.
It is not always simple to compute the proper value for size. The
value is used by __builtin_apply to compute the amount of data
that should be pushed on the stack and copied from the incoming argument
area.
__builtin_apply.
typeof
Another way to refer to the type of an expression is with typeof.
The syntax of using of this keyword looks like sizeof, but the
construct acts semantically like a type name defined with typedef.
There are two ways of writing the argument to typeof: with an
expression or with a type. Here is an example with an expression:
typeof (x[0](1)) |
This assumes that x is an array of pointers to functions;
the type described is that of the values of the functions.
Here is an example with a typename as the argument:
typeof (int *) |
Here the type described is that of pointers to int.
If you are writing a header file that must work when included in ISO C
programs, write __typeof__ instead of typeof.
See section 5.39 Alternate Keywords.
A typeof-construct can be used anywhere a typedef name could be
used. For example, you can use it in a declaration, in a cast, or inside
of sizeof or typeof.
typeof is often useful in conjunction with the
statements-within-expressions feature. Here is how the two together can
be used to define a safe "maximum" macro that operates on any
arithmetic type and evaluates each of its arguments exactly once:
#define max(a,b) \
({ typeof (a) _a = (a); \
typeof (b) _b = (b); \
_a > _b ? _a : _b; })
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The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within the
expressions that are substituted for a and b. Eventually we
hope to design a new form of declaration syntax that allows you to declare
variables whose scopes start only after their initializers; this will be a
more reliable way to prevent such conflicts.
Some more examples of the use of typeof:
y with the type of what x points to.
typeof (*x) y; |
y as an array of such values.
typeof (*x) y[4]; |
y as an array of pointers to characters:
typeof (typeof (char *)[4]) y; |
It is equivalent to the following traditional C declaration:
char *y[4]; |
To see the meaning of the declaration using typeof, and why it
might be a useful way to write, let's rewrite it with these macros:
#define pointer(T) typeof(T *) #define array(T, N) typeof(T [N]) |
Now the declaration can be rewritten this way:
array (pointer (char), 4) y; |
Thus, array (pointer (char), 4) is the type of arrays of 4
pointers to char.
Compatibility Note: In addition to typeof, GCC 2 supported
a more limited extension which permitted one to write
typedef T = expr; |
with the effect of declaring T to have the type of the expression
expr. This extension does not work with GCC 3 (versions between
3.0 and 3.2 will crash; 3.2.1 and later give an error). Code which
relies on it should be rewritten to use typeof:
typedef typeof(expr) T; |
This will work with all versions of GCC.
Compound expressions, conditional expressions and casts are allowed as lvalues provided their operands are lvalues. This means that you can take their addresses or store values into them.
All these extensions are deprecated.
For example, a compound expression can be assigned, provided the last expression in the sequence is an lvalue. These two expressions are equivalent:
(a, b) += 5 a, (b += 5) |
Similarly, the address of the compound expression can be taken. These two expressions are equivalent:
&(a, b) a, &b |
A conditional expression is a valid lvalue if its type is not void and the true and false branches are both valid lvalues. For example, these two expressions are equivalent:
(a ? b : c) = 5 (a ? b = 5 : (c = 5)) |
A cast is a valid lvalue if its operand is an lvalue. A simple
assignment whose left-hand side is a cast works by converting the
right-hand side first to the specified type, then to the type of the
inner left-hand side expression. After this is stored, the value is
converted back to the specified type to become the value of the
assignment. Thus, if a has type char *, the following two
expressions are equivalent:
(int)a = 5 (int)(a = (char *)(int)5) |
An assignment-with-arithmetic operation such as `+=' applied to a cast performs the arithmetic using the type resulting from the cast, and then continues as in the previous case. Therefore, these two expressions are equivalent:
(int)a += 5 (int)(a = (char *)(int) ((int)a + 5)) |
You cannot take the address of an lvalue cast, because the use of its
address would not work out coherently. Suppose that &(int)f were
permitted, where f has type float. Then the following
statement would try to store an integer bit-pattern where a floating
point number belongs:
*&(int)f = 1; |
This is quite different from what (int)f = 1 would do--that
would convert 1 to floating point and store it. Rather than cause this
inconsistency, we think it is better to prohibit use of `&' on a cast.
If you really do want an int * pointer with the address of
f, you can simply write (int *)&f.
The middle operand in a conditional expression may be omitted. Then if the first operand is nonzero, its value is the value of the conditional expression.
Therefore, the expression
x ? : y |
has the value of x if that is nonzero; otherwise, the value of
y.
This example is perfectly equivalent to
x ? x : y |
In this simple case, the ability to omit the middle operand is not especially useful. When it becomes useful is when the first operand does, or may (if it is a macro argument), contain a side effect. Then repeating the operand in the middle would perform the side effect twice. Omitting the middle operand uses the value already computed without the undesirable effects of recomputing it.
ISO C99 supports data types for integers that are at least 64 bits wide,
and as an extension GCC supports them in C89 mode and in C++.
Simply write long long int for a signed integer, or
unsigned long long int for an unsigned integer. To make an
integer constant of type long long int, add the suffix `LL'
to the integer. To make an integer constant of type unsigned long
long int, add the suffix `ULL' to the integer.
You can use these types in arithmetic like any other integer types. Addition, subtraction, and bitwise boolean operations on these types are open-coded on all types of machines. Multiplication is open-coded if the machine supports fullword-to-doubleword a widening multiply instruction. Division and shifts are open-coded only on machines that provide special support. The operations that are not open-coded use special library routines that come with GCC.
There may be pitfalls when you use long long types for function
arguments, unless you declare function prototypes. If a function
expects type int for its argument, and you pass a value of type
long long int, confusion will result because the caller and the
subroutine will disagree about the number of bytes for the argument.
Likewise, if the function expects long long int and you pass
int. The best way to avoid such problems is to use prototypes.
ISO C99 supports complex floating data types, and as an extension GCC
supports them in C89 mode and in C++, and supports complex integer data
types which are not part of ISO C99. You can declare complex types
using the keyword _Complex. As an extension, the older GNU
keyword __complex__ is also supported.
For example, `_Complex double x;' declares x as a
variable whose real part and imaginary part are both of type
double. `_Complex short int y;' declares y to
have real and imaginary parts of type short int; this is not
likely to be useful, but it shows that the set of complex types is
complete.
To write a constant with a complex data type, use the suffix `i' or
`j' (either one; they are equivalent). For example, 2.5fi
has type _Complex float and 3i has type
_Complex int. Such a constant always has a pure imaginary
value, but you can form any complex value you like by adding one to a
real constant. This is a GNU extension; if you have an ISO C99
conforming C library (such as GNU libc), and want to construct complex
constants of floating type, you should include <complex.h> and
use the macros I or _Complex_I instead.
To extract the real part of a complex-valued expression exp, write
__real__ exp. Likewise, use __imag__ to
extract the imaginary part. This is a GNU extension; for values of
floating type, you should use the ISO C99 functions crealf,
creal, creall, cimagf, cimag and
cimagl, declared in <complex.h> and also provided as
built-in functions by GCC.
The operator `~' performs complex conjugation when used on a value
with a complex type. This is a GNU extension; for values of
floating type, you should use the ISO C99 functions conjf,
conj and conjl, declared in <complex.h> and also
provided as built-in functions by GCC.
GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice-versa). Only the DWARF2
debug info format can represent this, so use of DWARF2 is recommended.
If you are using the stabs debug info format, GCC describes a noncontiguous
complex variable as if it were two separate variables of noncomplex type.
If the variable's actual name is foo, the two fictitious
variables are named foo$real and foo$imag. You can
examine and set these two fictitious variables with your debugger.
ISO C99 supports floating-point numbers written not only in the usual
decimal notation, such as 1.55e1, but also numbers such as
0x1.fp3 written in hexadecimal format. As a GNU extension, GCC
supports this in C89 mode (except in some cases when strictly
conforming) and in C++. In that format the
`0x' hex introducer and the `p' or `P' exponent field are
mandatory. The exponent is a decimal number that indicates the power of
2 by which the significant part will be multiplied. Thus `0x1.f' is
1 15/16,
`p3' multiplies it by 8, and the value of 0x1.fp3
is the same as 1.55e1.
Unlike for floating-point numbers in the decimal notation the exponent
is always required in the hexadecimal notation. Otherwise the compiler
would not be able to resolve the ambiguity of, e.g., 0x1.f. This
could mean 1.0f or 1.9375 since `f' is also the
extension for floating-point constants of type float.
Zero-length arrays are allowed in GNU C. They are very useful as the last element of a structure which is really a header for a variable-length object:
struct line {
int length;
char contents[0];
};
struct line *thisline = (struct line *)
malloc (sizeof (struct line) + this_length);
thisline->length = this_length;
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In ISO C90, you would have to give contents a length of 1, which
means either you waste space or complicate the argument to malloc.
In ISO C99, you would use a flexible array member, which is slightly different in syntax and semantics:
contents[] without
the 0.
sizeof
operator may not be applied. As a quirk of the original implementation
of zero-length arrays, sizeof evaluates to zero.
struct that is otherwise non-empty.
GCC versions before 3.0 allowed zero-length arrays to be statically initialized, as if they were flexible arrays. In addition to those cases that were useful, it also allowed initializations in situations that would corrupt later data. Non-empty initialization of zero-length arrays is now treated like any case where there are more initializer elements than the array holds, in that a suitable warning about "excess elements in array" is given, and the excess elements (all of them, in this case) are ignored.
Instead GCC allows static initialization of flexible array members.
This is equivalent to defining a new structure containing the original
structure followed by an array of sufficient size to contain the data.
I.e. in the following, f1 is constructed as if it were declared
like f2.
struct f1 {
int x; int y[];
} f1 = { 1, { 2, 3, 4 } };
struct f2 {
struct f1 f1; int data[3];
} f2 = { { 1 }, { 2, 3, 4 } };
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The convenience of this extension is that f1 has the desired
type, eliminating the need to consistently refer to f2.f1.
This has symmetry with normal static arrays, in that an array of
unknown size is also written with [].
Of course, this extension only makes sense if the extra data comes at the end of a top-level object, as otherwise we would be overwriting data at subsequent offsets. To avoid undue complication and confusion with initialization of deeply nested arrays, we simply disallow any non-empty initialization except when the structure is the top-level object. For example:
struct foo { int x; int y[]; };
struct bar { struct foo z; };
struct foo a = { 1, { 2, 3, 4 } }; // Valid.
struct bar b = { { 1, { 2, 3, 4 } } }; // Invalid.
struct bar c = { { 1, { } } }; // Valid.
struct foo d[1] = { { 1 { 2, 3, 4 } } }; // Invalid.
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GCC permits a C structure to have no members:
struct empty {
};
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The structure will have size zero. In C++, empty structures are part
of the language. G++ treats empty structures as if they had a single
member of type char.
Variable-length automatic arrays are allowed in ISO C99, and as an extension GCC accepts them in C89 mode and in C++. (However, GCC's implementation of variable-length arrays does not yet conform in detail to the ISO C99 standard.) These arrays are declared like any other automatic arrays, but with a length that is not a constant expression. The storage is allocated at the point of declaration and deallocated when the brace-level is exited. For example:
FILE *
concat_fopen (char *s1, char *s2, char *mode)
{
char str[strlen (s1) + strlen (s2) + 1];
strcpy (str, s1);
strcat (str, s2);
return fopen (str, mode);
}
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Jumping or breaking out of the scope of the array name deallocates the storage. Jumping into the scope is not allowed; you get an error message for it.
You can use the function alloca to get an effect much like
variable-length arrays. The function alloca is available in
many other C implementations (but not in all). On the other hand,
variable-length arrays are more elegant.
There are other differences between these two methods. Space allocated
with alloca exists until the containing function returns.
The space for a variable-length array is deallocated as soon as the array
name's scope ends. (If you use both variable-length arrays and
alloca in the same function, deallocation of a variable-length array
will also deallocate anything more recently allocated with alloca.)
You can also use variable-length arrays as arguments to functions:
struct entry
tester (int len, char data[len][len])
{
/* ... */
}
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The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
sizeof.
If you want to pass the array first and the length afterward, you can use a forward declaration in the parameter list--another GNU extension.
struct entry
tester (int len; char data[len][len], int len)
{
/* ... */
}
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The `int len' before the semicolon is a parameter forward
declaration, and it serves the purpose of making the name len
known when the declaration of data is parsed.
You can write any number of such parameter forward declarations in the parameter list. They can be separated by commas or semicolons, but the last one must end with a semicolon, which is followed by the "real" parameter declarations. Each forward declaration must match a "real" declaration in parameter name and data type. ISO C99 does not support parameter forward declarations.
In the ISO C standard of 1999, a macro can be declared to accept a variable number of arguments much as a function can. The syntax for defining the macro is similar to that of a function. Here is an example:
#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__) |
Here `...' is a variable argument. In the invocation of
such a macro, it represents the zero or more tokens until the closing
parenthesis that ends the invocation, including any commas. This set of
tokens replaces the identifier __VA_ARGS__ in the macro body
wherever it appears. See the CPP manual for more information.
GCC has long supported variadic macros, and used a different syntax that allowed you to give a name to the variable arguments just like any other argument. Here is an example:
#define debug(format, args...) fprintf (stderr, format, args) |
This is in all ways equivalent to the ISO C example above, but arguably more readable and descriptive.
GNU CPP has two further variadic macro extensions, and permits them to be used with either of the above forms of macro definition.
In standard C, you are not allowed to leave the variable argument out entirely; but you are allowed to pass an empty argument. For example, this invocation is invalid in ISO C, because there is no comma after the string:
debug ("A message")
|
GNU CPP permits you to completely omit the variable arguments in this way. In the above examples, the compiler would complain, though since the expansion of the macro still has the extra comma after the format string.
To help solve this problem, CPP behaves specially for variable arguments used with the token paste operator, `##'. If instead you write
#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__) |
and if the variable arguments are omitted or empty, the `##' operator causes the preprocessor to remove the comma before it. If you do provide some variable arguments in your macro invocation, GNU CPP does not complain about the paste operation and instead places the variable arguments after the comma. Just like any other pasted macro argument, these arguments are not macro expanded.
Recently, the preprocessor has relaxed its treatment of escaped newlines. Previously, the newline had to immediately follow a backslash. The current implementation allows whitespace in the form of spaces, horizontal and vertical tabs, and form feeds between the backslash and the subsequent newline. The preprocessor issues a warning, but treats it as a valid escaped newline and combines the two lines to form a single logical line. This works within comments and tokens, as well as between tokens. Comments are not treated as whitespace for the purposes of this relaxation, since they have not yet been replaced with spaces.
In ISO C99, arrays that are not lvalues still decay to pointers, and may be subscripted, although they may not be modified or used after the next sequence point and the unary `&' operator may not be applied to them. As an extension, GCC allows such arrays to be subscripted in C89 mode, though otherwise they do not decay to pointers outside C99 mode. For example, this is valid in GNU C though not valid in C89:
struct foo {int a[4];};
struct foo f();
bar (int index)
{
return f().a[index];
}
|
void- and Function-Pointers
In GNU C, addition and subtraction operations are supported on pointers to
void and on pointers to functions. This is done by treating the
size of a void or of a function as 1.
A consequence of this is that sizeof is also allowed on void
and on function types, and returns 1.
The option `-Wpointer-arith' requests a warning if these extensions are used.
As in standard C++ and ISO C99, the elements of an aggregate initializer for an automatic variable are not required to be constant expressions in GNU C. Here is an example of an initializer with run-time varying elements:
foo (float f, float g)
{
float beat_freqs[2] = { f-g, f+g };
/* ... */
}
|
ISO C99 supports compound literals. A compound literal looks like a cast containing an initializer. Its value is an object of the type specified in the cast, containing the elements specified in the initializer; it is an lvalue. As an extension, GCC supports compound literals in C89 mode and in C++.
Usually, the specified type is a structure. Assume that
struct foo and structure are declared as shown:
struct foo {int a; char b[2];} structure;
|
Here is an example of constructing a struct foo with a compound literal:
structure = ((struct foo) {x + y, 'a', 0});
|
This is equivalent to writing the following:
{
struct foo temp = {x + y, 'a', 0};
structure = temp;
}
|
You can also construct an array. If all the elements of the compound literal are (made up of) simple constant expressions, suitable for use in initializers of objects of static storage duration, then the compound literal can be coerced to a pointer to its first element and used in such an initializer, as shown here:
char **foo = (char *[]) { "x", "y", "z" };
|
Compound literals for scalar types and union types are is also allowed, but then the compound literal is equivalent to a cast.
As a GNU extension, GCC allows initialization of objects with static storage duration by compound literals (which is not possible in ISO C99, because the initializer is not a constant). It is handled as if the object was initialized only with the bracket enclosed list if compound literal's and object types match. The initializer list of the compound literal must be constant. If the object being initialized has array type of unknown size, the size is determined by compound literal size.
static struct foo x = (struct foo) {1, 'a', 'b'};
static int y[] = (int []) {1, 2, 3};
static int z[] = (int [3]) {1};
|
The above lines are equivalent to the following:
static struct foo x = {1, 'a', 'b'};
static int y[] = {1, 2, 3};
static int z[] = {1, 0, 0};
|
Standard C89 requires the elements of an initializer to appear in a fixed order, the same as the order of the elements in the array or structure being initialized.
In ISO C99 you can give the elements in any order, specifying the array indices or structure field names they apply to, and GNU C allows this as an extension in C89 mode as well. This extension is not implemented in GNU C++.
To specify an array index, write `[index] =' before the element value. For example,
int a[6] = { [4] = 29, [2] = 15 };
|
is equivalent to
int a[6] = { 0, 0, 15, 0, 29, 0 };
|
The index values must be constant expressions, even if the array being initialized is automatic.
An alternative syntax for this which has been obsolete since GCC 2.5 but GCC still accepts is to write `[index]' before the element value, with no `='.
To initialize a range of elements to the same value, write `[first ... last] = value'. This is a GNU extension. For example,
int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };
|
If the value in it has side-effects, the side-effects will happen only once, not for each initialized field by the range initializer.
Note that the length of the array is the highest value specified plus one.
In a structure initializer, specify the name of a field to initialize with `.fieldname =' before the element value. For example, given the following structure,
struct point { int x, y; };
|
the following initialization
struct point p = { .y = yvalue, .x = xvalue };
|
is equivalent to
struct point p = { xvalue, yvalue };
|
Another syntax which has the same meaning, obsolete since GCC 2.5, is `fieldname:', as shown here:
struct point p = { y: yvalue, x: xvalue };
|
The `[index]' or `.fieldname' is known as a designator. You can also use a designator (or the obsolete colon syntax) when initializing a union, to specify which element of the union should be used. For example,
union foo { int i; double d; };
union foo f = { .d = 4 };
|
will convert 4 to a double to store it in the union using
the second element. By contrast, casting 4 to type union foo
would store it into the union as the integer i, since it is
an integer. (See section 5.23 Cast to a Union Type.)
You can combine this technique of naming elements with ordinary C initialization of successive elements. Each initializer element that does not have a designator applies to the next consecutive element of the array or structure. For example,
int a[6] = { [1] = v1, v2, [4] = v4 };
|
is equivalent to
int a[6] = { 0, v1, v2, 0, v4, 0 };
|
Labeling the elements of an array initializer is especially useful
when the indices are characters or belong to an enum type.
For example:
int whitespace[256]
= { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };
|
You can also write a series of `.fieldname' and `[index]' designators before an `=' to specify a nested subobject to initialize; the list is taken relative to the subobject corresponding to the closest surrounding brace pair. For example, with the `struct point' declaration above:
struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };
|
If the same field is initialized multiple times, it will have value from the last initialization. If any such overridden initialization has side-effect, it is unspecified whether the side-effect happens or not. Currently, gcc will discard them and issue a warning.
You can specify a range of consecutive values in a single case label,
like this:
case low ... high: |
This has the same effect as the proper number of individual case
labels, one for each integer value from low to high, inclusive.
This feature is especially useful for ranges of ASCII character codes:
case 'A' ... 'Z': |
Be careful: Write spaces around the ..., for otherwise
it may be parsed wrong when you use it with integer values. For example,
write this:
case 1 ... 5: |
rather than this:
case 1...5: |
A cast to union type is similar to other casts, except that the type
specified is a union type. You can specify the type either with
union tag or with a typedef name. A cast to union is actually
a constructor though, not a cast, and hence does not yield an lvalue like
normal casts. (See section 5.20 Compound Literals.)
The types that may be cast to the union type are those of the members of the union. Thus, given the following union and variables:
union foo { int i; double d; };
int x;
double y;
|
both x and y can be cast to type union foo.
Using the cast as the right-hand side of an assignment to a variable of union type is equivalent to storing in a member of the union:
union foo u; /* ... */ u = (union foo) x == u.i = x u = (union foo) y == u.d = y |
You can also use the union cast as a function argument:
void hack (union foo); /* ... */ hack ((union foo) x); |
ISO C99 and ISO C++ allow declarations and code to be freely mixed within compound statements. As an extension, GCC also allows this in C89 mode. For example, you could do:
int i; /* ... */ i++; int j = i + 2; |
Each identifier is visible from where it is declared until the end of the enclosing block.
In GNU C, you declare certain things about functions called in your program which help the compiler optimize function calls and check your code more carefully.
The keyword __attribute__ allows you to specify special
attributes when making a declaration. This keyword is followed by an
attribute specification inside double parentheses. The following
attributes are currently defined for functions on all targets:
noreturn, noinline, always_inline,
pure, const, nothrow,
format, format_arg, no_instrument_function,
section, constructor, destructor, used,
unused, deprecated, weak, malloc,
alias, and nonnull. Several other attributes are defined
for functions on particular target systems. Other attributes, including
section are supported for variables declarations
(see section 5.32 Specifying Attributes of Variables) and for types (see section 5.33 Specifying Attributes of Types).
You may also specify attributes with `__' preceding and following
each keyword. This allows you to use them in header files without
being concerned about a possible macro of the same name. For example,
you may use __noreturn__ instead of noreturn.
See section 5.26 Attribute Syntax, for details of the exact syntax for using attributes.
noreturn
abort and exit,
cannot return. GCC knows this automatically. Some programs define
their own functions that never return. You can declare them
noreturn to tell the compiler this fact. For example,
void fatal () __attribute__ ((noreturn));
void
fatal (/* ... */)
{
/* ... */ /* Print error message. */ /* ... */
exit (1);
}
|
The noreturn keyword tells the compiler to assume that
fatal cannot return. It can then optimize without regard to what
would happen if fatal ever did return. This makes slightly
better code. More importantly, it helps avoid spurious warnings of
uninitialized variables.
Do not assume that registers saved by the calling function are
restored before calling the noreturn function.
It does not make sense for a noreturn function to have a return
type other than void.
The attribute noreturn is not implemented in GCC versions
earlier than 2.5. An alternative way to declare that a function does
not return, which works in the current version and in some older
versions, is as follows:
typedef void voidfn (); volatile voidfn fatal; |
noinline
always_inline
pure
pure. For example,
int square (int) __attribute__ ((pure)); |
says that the hypothetical function square is safe to call
fewer times than the program says.
Some of common examples of pure functions are strlen or memcmp.
Interesting non-pure functions are functions with infinite loops or those
depending on volatile memory or other system resource, that may change between
two consecutive calls (such as feof in a multithreading environment).
The attribute pure is not implemented in GCC versions earlier
than 2.96.
const
pure attribute above, since function is not
allowed to read global memory.
Note that a function that has pointer arguments and examines the data
pointed to must not be declared const. Likewise, a
function that calls a non-const function usually must not be
const. It does not make sense for a const function to
return void.
The attribute const is not implemented in GCC versions earlier
than 2.5. An alternative way to declare that a function has no side
effects, which works in the current version and in some older versions,
is as follows:
typedef int intfn (); extern const intfn square; |
This approach does not work in GNU C++ from 2.6.0 on, since the language specifies that the `const' must be attached to the return value.
nothrow
nothrow attribute is used to inform the compiler that a
function cannot throw an exception. For example, most functions in
the standard C library can be guaranteed not to throw an exception
with the notable exceptions of qsort and bsearch that
take function pointer arguments. The nothrow attribute is not
implemented in GCC versions earlier than 3.2.
format (archetype, string-index, first-to-check)
format attribute specifies that a function takes printf,
scanf, strftime or strfmon style arguments which
should be type-checked against a format string. For example, the
declaration:
extern int
my_printf (void *my_object, const char *my_format, ...)
__attribute__ ((format (printf, 2, 3)));
|
causes the compiler to check the arguments in calls to my_printf
for consistency with the printf style format string argument
my_format.
The parameter archetype determines how the format string is
interpreted, and should be printf, scanf, strftime
or strfmon. (You can also use __printf__,
__scanf__, __strftime__ or __strfmon__.) The
parameter string-index specifies which argument is the format
string argument (starting from 1), while first-to-check is the
number of the first argument to check against the format string. For
functions where the arguments are not available to be checked (such as
vprintf), specify the third parameter as zero. In this case the
compiler only checks the format string for consistency. For
strftime formats, the third parameter is required to be zero.
Since non-static C++ methods have an implicit this argument, the
arguments of such methods should be counted from two, not one, when
giving values for string-index and first-to-check.
In the example above, the format string (my_format) is the second
argument of the function my_print, and the arguments to check
start with the third argument, so the correct parameters for the format
attribute are 2 and 3.
The format attribute allows you to identify your own functions
which take format strings as arguments, so that GCC can check the
calls to these functions for errors. The compiler always (unless
`-ffreestanding' is used) checks formats
for the standard library functions printf, fprintf,
sprintf, scanf, fscanf, sscanf, strftime,
vprintf, vfprintf and vsprintf whenever such
warnings are requested (using `-Wformat'), so there is no need to
modify the header file `stdio.h'. In C99 mode, the functions
snprintf, vsnprintf, vscanf, vfscanf and
vsscanf are also checked. Except in strictly conforming C
standard modes, the X/Open function strfmon is also checked as
are printf_unlocked and fprintf_unlocked.
See section Options Controlling C Dialect.
format_arg (string-index)
format_arg attribute specifies that a function takes a format
string for a printf, scanf, strftime or
strfmon style function and modifies it (for example, to translate
it into another language), so the result can be passed to a
printf, scanf, strftime or strfmon style
function (with the remaining arguments to the format function the same
as they would have been for the unmodified string). For example, the
declaration:
extern char *
my_dgettext (char *my_domain, const char *my_format)
__attribute__ ((format_arg (2)));
|
causes the compiler to check the arguments in calls to a printf,
scanf, strftime or strfmon type function, whose
format string argument is a call to the my_dgettext function, for
consistency with the format string argument my_format. If the
format_arg attribute had not been specified, all the compiler
could tell in such calls to format functions would be that the format
string argument is not constant; this would generate a warning when
`-Wformat-nonliteral' is used, but the calls could not be checked
without the attribute.
The parameter string-index specifies which argument is the format
string argument (starting from one). Since non-static C++ methods have
an implicit this argument, the arguments of such methods should
be counted from two.
The format-arg attribute allows you to identify your own
functions which modify format strings, so that GCC can check the
calls to printf, scanf, strftime or strfmon
type function whose operands are a call to one of your own function.
The compiler always treats gettext, dgettext, and
dcgettext in this manner except when strict ISO C support is
requested by `-ansi' or an appropriate `-std' option, or
`-ffreestanding' is used. See section Options Controlling C Dialect.
nonnull (arg-index, ...)
nonnull attribute specifies that some function parameters should
be non-null pointers. For instance, the declaration:
extern void * my_memcpy (void *dest, const void *src, size_t len) __attribute__((nonnull (1, 2))); |
causes the compiler to check that, in calls to my_memcpy,
arguments dest and src are non-null. If the compiler
determines that a null pointer is passed in an argument slot marked
as non-null, and the `-Wnonnull' option is enabled, a warning
is issued. The compiler may also choose to make optimizations based
on the knowledge that certain function arguments will not be null.
If no argument index list is given to the nonnull attribute,
all pointer arguments are marked as non-null. To illustrate, the
following declaration is equivalent to the previous example:
extern void * my_memcpy (void *dest, const void *src, size_t len) __attribute__((nonnull)); |
no_instrument_function
section ("section-name")
text section.
Sometimes, however, you need additional sections, or you need certain
particular functions to appear in special sections. The section
attribute specifies that a function lives in a particular section.
For example, the declaration:
extern void foobar (void) __attribute__ ((section ("bar")));
|
puts the function foobar in the bar section.
Some file formats do not support arbitrary sections so the section
attribute is not available on all platforms.
If you need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.
constructor
destructor
constructor attribute causes the function to be called
automatically before execution enters main (). Similarly, the
destructor attribute causes the function to be called
automatically after main () has completed or exit () has
been called. Functions with these attributes are useful for
initializing data that will be used implicitly during the execution of
the program.
These attributes are not currently implemented for Objective-C.
unused
used
deprecated
deprecated attribute results in a warning if the function
is used anywhere in the source file. This is useful when identifying
functions that are expected to be removed in a future version of a
program. The warning also includes the location of the declaration
of the deprecated function, to enable users to easily find further
information about why the function is deprecated, or what they should
do instead. Note that the warnings only occurs for uses:
int old_fn () __attribute__ ((deprecated)); int old_fn (); int (*fn_ptr)() = old_fn; |
results in a warning on line 3 but not line 2.
The deprecated attribute can also be used for variables and
types (see section 5.32 Specifying Attributes of Variables, see section 5.33 Specifying Attributes of Types.)
weak
weak attribute causes the declaration to be emitted as a weak
symbol rather than a global. This is primarily useful in defining
library functions which can be overridden in user code, though it can
also be used with non-function declarations. Weak symbols are supported
for ELF targets, and also for a.out targets when using the GNU assembler
and linker.
malloc
malloc attribute is used to tell the compiler that a function
may be treated as if it were the malloc function. The compiler assumes
that calls to malloc result in pointers that cannot alias anything.
This will often improve optimization.
alias ("target")
alias attribute causes the declaration to be emitted as an
alias for another symbol, which must be specified. For instance,
void __f () { /* Do something. */; }
void f () __attribute__ ((weak, alias ("__f")));
|
declares `f' to be a weak alias for `__f'. In C++, the mangled name for the target must be used.
Not all target machines support this attribute.
visibility ("visibility_type")
visibility attribute on ELF targets causes the declaration
to be emitted with default, hidden, protected or internal visibility.
void __attribute__ ((visibility ("protected")))
f () { /* Do something. */; }
int i __attribute__ ((visibility ("hidden")));
|
See the ELF gABI for complete details, but the short story is:
Not all ELF targets support this attribute.
regparm (number)
regparm attribute causes the compiler to
pass up to number integer arguments in registers EAX,
EDX, and ECX instead of on the stack. Functions that take a
variable number of arguments will continue to be passed all of their
arguments on the stack.
Beware that on some ELF systems this attribute is unsuitable for global functions in shared libraries with lazy binding (which is the default). Lazy binding will send the first call via resolving code in the loader, which might assume EAX, EDX and ECX can be clobbered, as per the standard calling conventions. Solaris 8 is affected by this. GNU systems with GLIBC 2.1 or higher, and FreeBSD, are believed to be safe since the loaders there save all registers. (Lazy binding can be disabled with the linker or the loader if desired, to avoid the problem.)
stdcall
stdcall attribute causes the compiler to
assume that the called function will pop off the stack space used to
pass arguments, unless it takes a variable number of arguments.
cdecl
cdecl attribute causes the compiler to
assume that the calling function will pop off the stack space used to
pass arguments. This is
useful to override the effects of the `-mrtd' switch.
longcall/shortcall
longcall attribute causes the
compiler to always call this function via a pointer, just as it would if
the `-mlongcall' option had been specified. The shortcall
attribute causes the compiler not to do this. These attributes override
both the `-mlongcall' switch and the #pragma longcall
setting.
See section 3.17.10 IBM RS/6000 and PowerPC Options, for more information on whether long calls are necessary.
long_call/short_call
#pragma long_calls settings. The
long_call attribute causes the compiler to always call the
function by first loading its address into a register and then using the
contents of that register. The short_call attribute always places
the offset to the function from the call site into the `BL'
instruction directly.
function_vector
You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.
interrupt
Note, interrupt handlers for the H8/300, H8/300H and SH processors can
be specified via the interrupt_handler attribute.
Note, on the AVR, interrupts will be enabled inside the function.
Note, for the ARM, you can specify the kind of interrupt to be handled by adding an optional parameter to the interrupt attribute like this:
void f () __attribute__ ((interrupt ("IRQ")));
|
Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF.
interrupt_handler
sp_switch
interrupt_handler
function should switch to an alternate stack. It expects a string
argument that names a global variable holding the address of the
alternate stack.
void *alt_stack;
void f () __attribute__ ((interrupt_handler,
sp_switch ("alt_stack")));
|
trap_exit
interrupt_handle to return using
trapa instead of rte. This attribute expects an integer
argument specifying the trap number to be used.
eightbit_data
You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.
tiny_data
signal
naked
model (model-name)
small, medium,
or large, representing each of the code models.
Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the ld24 instruction), and are
callable with the bl instruction.
Medium model objects may live anywhere in the 32-bit address space (the
compiler will generate seth/add3 instructions to load their addresses),
and are callable with the bl instruction.
Large model objects may live anywhere in the 32-bit address space (the
compiler will generate seth/add3 instructions to load their addresses),
and may not be reachable with the bl instruction (the compiler will
generate the much slower seth/add3/jl instruction sequence).
far
far attribute causes the compiler to
use a calling convention that takes care of switching memory banks when
entering and leaving a function. This calling convention is also the
default when using the `-mlong-calls' option.
On 68HC12 the compiler will use the call and rtc instructions
to call and return from a function.
On 68HC11 the compiler will generate a sequence of instructions
to invoke a board-specific routine to switch the memory bank and call the
real function. The board-specific routine simulates a call.
At the end of a function, it will jump to a board-specific routine
instead of using rts. The board-specific return routine simulates
the rtc.
The far attribute must not be used when the interrupt or
trap attributes are used.
near
near attribute causes the compiler to
use the normal calling convention based on jsr and rts.
This attribute can be used to cancel the effect of the `-mlong-calls'
option.
page0
page0 attribute indicates that a global
or static variable is put in the page0 section and the compiler can
use the direct addressing mode. On 68HC11 the compiler will be able to
use bset and bclr on these variables. Note that the page0
is limited to the absolute address range 0..0x0ff.
trap
trap attribute marks the function as being
a trap handler. It will use rti instead of rts to return
from the function. Offset of function parameters are also adjusted to take
into account the trap frame.
dllimport
dllimport attribute causes the compiler
to reference a function or variable via a global pointer to a pointer
that is set up by the Windows dll library. The pointer name is formed by
combining _imp__ and the function or variable name. The attribute
implies extern storage.
Currently, the attribute is ignored for inlined functions. If the
attribute is applied to a symbol definition, an error is reported.
If a symbol previously declared dllimport is later defined, the
attribute is ignored in subsequent references, and a warning is emitted.
The attribute is also overridden by a subsequent declaration as
dllexport.
When applied to C++ classes, the attribute marks non-inlined member functions and static data members as imports. However, the attribute is ignored for virtual methods to allow creation of vtables using thunks.
On cygwin, mingw and arm-pe targets, __declspec(dllimport) is
recognized as a synonym for __attribute__ ((dllimport)) for
compatibility with other Windows compilers.
The use of the dllimport attribute on functions is not necessary,
but provides a small performance benefit by eliminating a thunk in the
dll. The use of the dllimport attribute on imported variables was
required on older versions of GNU ld, but can now be avoided by passing
the `--enable-auto-import' switch to ld. As with functions, using
the attribute for a variable eliminates a thunk in the dll.
One drawback to using this attribute is that a pointer to a function or variable marked as dllimport cannot be used as a constant address. The attribute can be disabled for functions by setting the `-mnop-fun-dllimport' flag.
dllexport
dllexport attribute causes the compiler to
provide a global pointer to a pointer in a dll, so that it can be
referenced with the dllimport attribute. The pointer name is
formed by combining _imp__ and the function or variable name.
Currently, the dllexportattribute is ignored for inlined
functions, but export can be forced by using the
`-fkeep-inline-functions' flag. The attribute is also ignored for
undefined symbols.
When applied to C++ classes. the attribute marks defined non-inlined member functions and static data members as exports. Static consts initialized in-class are not marked unless they are also defined out-of-class.
On cygwin, mingw and arm-pe targets, __declspec(dllexport) is
recognized as a synonym for __attribute__ ((dllexport)) for
compatibility with other Windows compilers.
Alternative methods for including the symbol in the dll's export table
are to use a .def file with an EXPORTS section or, with GNU ld,
using the `--export-all' linker flag.
You can specify multiple attributes in a declaration by separating them by commas within the double parentheses or by immediately following an attribute declaration with another attribute declaration.
Some people object to the __attribute__ feature, suggesting that
ISO C's #pragma should be used instead. At the time
__attribute__ was designed, there were two reasons for not doing
this.
#pragma commands from a macro.
#pragma might mean in another
compiler.
These two reasons applied to almost any application that might have been
proposed for #pragma. It was basically a mistake to use
#pragma for anything.
The ISO C99 standard includes _Pragma, which now allows pragmas
to be generated from macros. In addition, a #pragma GCC
namespace is now in use for GCC-specific pragmas. However, it has been
found convenient to use __attribute__ to achieve a natural
attachment of attributes to their corresponding declarations, whereas
#pragma GCC is of use for constructs that do not naturally form
part of the grammar. See section `Miscellaneous Preprocessing Directives' in The GNU C Preprocessor.
This section describes the syntax with which __attribute__ may be
used, and the constructs to which attribute specifiers bind, for the C
language. Some details may vary for C++ and Objective-C. Because of
infelicities in the grammar for attributes, some forms described here
may not be successfully parsed in all cases.
There are some problems with the semantics of attributes in C++. For
example, there are no manglings for attributes, although they may affect
code generation, so problems may arise when attributed types are used in
conjunction with templates or overloading. Similarly, typeid
does not distinguish between types with different attributes. Support
for attributes in C++ may be restricted in future to attributes on
declarations only, but not on nested declarators.
See section 5.25 Declaring Attributes of Functions, for details of the semantics of attributes applying to functions. See section 5.32 Specifying Attributes of Variables, for details of the semantics of attributes applying to variables. See section 5.33 Specifying Attributes of Types, for details of the semantics of attributes applying to structure, union and enumerated types.
An attribute specifier is of the form
__attribute__ ((attribute-list)). An attribute list
is a possibly empty comma-separated sequence of attributes, where
each attribute is one of the following:
unused, or a reserved
word such as const).
mode attributes use this form.
format attributes use this form.
format_arg attributes use this form with the list being a single
integer constant expression, and alias attributes use this form
with the list being a single string constant.
An attribute specifier list is a sequence of one or more attribute specifiers, not separated by any other tokens.
An attribute specifier list may appear after the colon following a
label, other than a case or default label. The only
attribute it makes sense to use after a label is unused. This
feature is intended for code generated by programs which contains labels
that may be unused but which is compiled with `-Wall'. It would
not normally be appropriate to use in it human-written code, though it
could be useful in cases where the code that jumps to the label is
contained within an #ifdef conditional.
An attribute specifier list may appear as part of a struct,
union or enum specifier. It may go either immediately
after the struct, union or enum keyword, or after
the closing brace. It is ignored if the content of the structure, union
or enumerated type is not defined in the specifier in which the
attribute specifier list is used--that is, in usages such as
struct __attribute__((foo)) bar with no following opening brace.
Where attribute specifiers follow the closing brace, they are considered
to relate to the structure, union or enumerated type defined, not to any
enclosing declaration the type specifier appears in, and the type
defined is not complete until after the attribute specifiers.
Otherwise, an attribute specifier appears as part of a declaration, counting declarations of unnamed parameters and type names, and relates to that declaration (which may be nested in another declaration, for example in the case of a parameter declaration), or to a particular declarator within a declaration. Where an attribute specifier is applied to a parameter declared as a function or an array, it should apply to the function or array rather than the pointer to which the parameter is implicitly converted, but this is not yet correctly implemented.
Any list of specifiers and qualifiers at the start of a declaration may
contain attribute specifiers, whether or not such a list may in that
context contain storage class specifiers. (Some attributes, however,
are essentially in the nature of storage class specifiers, and only make
sense where storage class specifiers may be used; for example,
section.) There is one necessary limitation to this syntax: the
first old-style parameter declaration in a function definition cannot
begin with an attribute specifier, because such an attribute applies to
the function instead by syntax described below (which, however, is not
yet implemented in this case). In some other cases, attribute
specifiers are permitted by this grammar but not yet supported by the
compiler. All attribute specifiers in this place relate to the
declaration as a whole. In the obsolescent usage where a type of
int is implied by the absence of type specifiers, such a list of
specifiers and qualifiers may be an attribute specifier list with no
other specifiers or qualifiers.
An attribute specifier list may appear immediately before a declarator (other than the first) in a comma-separated list of declarators in a declaration of more than one identifier using a single list of specifiers and qualifiers. Such attribute specifiers apply only to the identifier before whose declarator they appear. For example, in
__attribute__((noreturn)) void d0 (void),
__attribute__((format(printf, 1, 2))) d1 (const char *, ...),
d2 (void)
|
the noreturn attribute applies to all the functions
declared; the format attribute only applies to d1.
An attribute specifier list may appear immediately before the comma,
= or semicolon terminating the declaration of an identifier other
than a function definition. At present, such attribute specifiers apply
to the declared object or function, but in future they may attach to the
outermost adjacent declarator. In simple cases there is no difference,
but, for example, in
void (****f)(void) __attribute__((noreturn)); |
at present the noreturn attribute applies to f, which
causes a warning since f is not a function, but in future it may
apply to the function ****f. The precise semantics of what
attributes in such cases will apply to are not yet specified. Where an
assembler name for an object or function is specified (see section 5.37 Controlling Names Used in Assembler Code), at present the attribute must follow the asm
specification; in future, attributes before the asm specification
may apply to the adjacent declarator, and those after it to the declared
object or function.
An attribute specifier list may, in future, be permitted to appear after the declarator in a function definition (before any old-style parameter declarations or the function body).
Attribute specifiers may be mixed with type qualifiers appearing inside
the [] of a parameter array declarator, in the C99 construct by
which such qualifiers are applied to the pointer to which the array is
implicitly converted. Such attribute specifiers apply to the pointer,
not to the array, but at present this is not implemented and they are
ignored.
An attribute specifier list may appear at the start of a nested
declarator. At present, there are some limitations in this usage: the
attributes correctly apply to the declarator, but for most individual
attributes the semantics this implies are not implemented.
When attribute specifiers follow the * of a pointer
declarator, they may be mixed with any type qualifiers present.
The following describes the formal semantics of this syntax. It will make the
most sense if you are familiar with the formal specification of
declarators in the ISO C standard.
Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration T
D1, where T contains declaration specifiers that specify a type
Type (such as int) and D1 is a declarator that
contains an identifier ident. The type specified for ident
for derived declarators whose type does not include an attribute
specifier is as in the ISO C standard.
If D1 has the form ( attribute-specifier-list D ),
and the declaration T D specifies the type
"derived-declarator-type-list Type" for ident, then
T D1 specifies the type "derived-declarator-type-list
attribute-specifier-list Type" for ident.
If D1 has the form *
type-qualifier-and-attribute-specifier-list D, and the
declaration T D specifies the type
"derived-declarator-type-list Type" for ident, then
T D1 specifies the type "derived-declarator-type-list
type-qualifier-and-attribute-specifier-list Type" for
ident.
For example,
void (__attribute__((noreturn)) ****f) (void); |
specifies the type "pointer to pointer to pointer to pointer to
non-returning function returning void". As another example,
char *__attribute__((aligned(8))) *f; |
specifies the type "pointer to 8-byte-aligned pointer to char".
Note again that this does not work with most attributes; for example,
the usage of `aligned' and `noreturn' attributes given above
is not yet supported.
For compatibility with existing code written for compiler versions that did not implement attributes on nested declarators, some laxity is allowed in the placing of attributes. If an attribute that only applies to types is applied to a declaration, it will be treated as applying to the type of that declaration. If an attribute that only applies to declarations is applied to the type of a declaration, it will be treated as applying to that declaration; and, for compatibility with code placing the attributes immediately before the identifier declared, such an attribute applied to a function return type will be treated as applying to the function type, and such an attribute applied to an array element type will be treated as applying to the array type. If an attribute that only applies to function types is applied to a pointer-to-function type, it will be treated as applying to the pointer target type; if such an attribute is applied to a function return type that is not a pointer-to-function type, it will be treated as applying to the function type.
GNU C extends ISO C to allow a function prototype to override a later old-style non-prototype definition. Consider the following example:
/* Use prototypes unless the compiler is old-fashioned. */
#ifdef __STDC__
#define P(x) x
#else
#define P(x) ()
#endif
/* Prototype function declaration. */
int isroot P((uid_t));
/* Old-style function definition. */
int
isroot (x) /* ??? lossage here ??? */
uid_t x;
{
return x == 0;
}
|
Suppose the type uid_t happens to be short. ISO C does
not allow this example, because subword arguments in old-style
non-prototype definitions are promoted. Therefore in this example the
function definition's argument is really an int, which does not
match the prototype argument type of short.
This restriction of ISO C makes it hard to write code that is portable
to traditional C compilers, because the programmer does not know
whether the uid_t type is short, int, or
long. Therefore, in cases like these GNU C allows a prototype
to override a later old-style definition. More precisely, in GNU C, a
function prototype argument type overrides the argument type specified
by a later old-style definition if the former type is the same as the
latter type before promotion. Thus in GNU C the above example is
equivalent to the following:
int isroot (uid_t);
int
isroot (uid_t x)
{
return x == 0;
}
|
GNU C++ does not support old-style function definitions, so this extension is irrelevant.
In GNU C, you may use C++ style comments, which start with `//' and continue until the end of the line. Many other C implementations allow such comments, and they are included in the 1999 C standard. However, C++ style comments are not recognized if you specify an `-std' option specifying a version of ISO C before C99, or `-ansi' (equivalent to `-std=c89').
In GNU C, you may normally use dollar signs in identifier names. This is because many traditional C implementations allow such identifiers. However, dollar signs in identifiers are not supported on a few target machines, typically because the target assembler does not allow them.
You can use the sequence `\e' in a string or character constant to stand for the ASCII character ESC.
The keyword __alignof__ allows you to inquire about how an object
is aligned, or the minimum alignment usually required by a type. Its
syntax is just like sizeof.
For example, if the target machine requires a double value to be
aligned on an 8-byte boundary, then __alignof__ (double) is 8.
This is true on many RISC machines. On more traditional machine
designs, __alignof__ (double) is 4 or even 2.
Some machines never actually require alignment; they allow reference to any
data type even at an odd address. For these machines, __alignof__
reports the recommended alignment of a type.
If the operand of __alignof__ is an lvalue rather than a type,
its value is the required alignment for its type, taking into account
any minimum alignment specified with GCC's __attribute__
extension (see section 5.32 Specifying Attributes of Variables). For example, after this
declaration:
struct foo { int x; char y; } foo1;
|
the value of __alignof__ (foo1.y) is 1, even though its actual
alignment is probably 2 or 4, the same as __alignof__ (int).
It is an error to ask for the alignment of an incomplete type.
The keyword __attribute__ allows you to specify special
attributes of variables or structure fields. This keyword is followed
by an attribute specification inside double parentheses. Some
attributes are currently defined generically for variables.
Other attributes are defined for variables on particular target
systems. Other attributes are available for functions
(see section 5.25 Declaring Attributes of Functions) and for types (see section 5.33 Specifying Attributes of Types).
Other front ends might define more attributes
(see section Extensions to the C++ Language).
You may also specify attributes with `__' preceding and following
each keyword. This allows you to use them in header files without
being concerned about a possible macro of the same name. For example,
you may use __aligned__ instead of aligned.
See section 5.26 Attribute Syntax, for details of the exact syntax for using attributes.
aligned (alignment)
int x __attribute__ ((aligned (16))) = 0; |
causes the compiler to allocate the global variable x on a
16-byte boundary. On a 68040, this could be used in conjunction with
an asm expression to access the move16 instruction which
requires 16-byte aligned operands.
You can also specify the alignment of structure fields. For example, to
create a double-word aligned int pair, you could write:
struct foo { int x[2] __attribute__ ((aligned (8))); };
|
This is an alternative to creating a union with a double member
that forces the union to be double-word aligned.
As in the preceding examples, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given variable or structure field. Alternatively, you can leave out the alignment factor and just ask the compiler to align a variable or field to the maximum useful alignment for the target machine you are compiling for. For example, you could write:
short array[3] __attribute__ ((aligned)); |
Whenever you leave out the alignment factor in an aligned attribute
specification, the compiler automatically sets the alignment for the declared
variable or field to the largest alignment which is ever used for any data
type on the target machine you are compiling for. Doing this can often make
copy operations more efficient, because the compiler can use whatever
instructions copy the biggest chunks of memory when performing copies to
or from the variables or fields that you have aligned this way.
The aligned attribute can only increase the alignment; but you
can decrease it by specifying packed as well. See below.
Note that the effectiveness of aligned attributes may be limited
by inherent limitations in your linker. On many systems, the linker is
only able to arrange for variables to be aligned up to a certain maximum
alignment. (For some linkers, the maximum supported alignment may
be very very small.) If your linker is only able to align variables
up to a maximum of 8 byte alignment, then specifying aligned(16)
in an __attribute__ will still only provide you with 8 byte
alignment. See your linker documentation for further information.
cleanup (cleanup_function)
cleanup attribute runs a function when the variable goes
out of scope. This attribute can only be applied to auto function
scope variables; it may not be applied to parameters or variables
with static storage duration. The function must take one parameter,
a pointer to a type compatible with the variable. The return value
of the function (if any) is ignored.
If `-fexceptions' is enabled, then cleanup_function
will be run during the stack unwinding that happens during the
processing of the exception. Note that the cleanup attribute
does not allow the exception to be caught, only to perform an action.
It is undefined what happens if cleanup_function does not
return normally.
common
nocommon
common attribute requests GCC to place a variable in
"common" storage. The nocommon attribute requests the
opposite -- to allocate space for it directly.
These attributes override the default chosen by the `-fno-common' and `-fcommon' flags respectively.
deprecated
deprecated attribute results in a warning if the variable
is used anywhere in the source file. This is useful when identifying
variables that are expected to be removed in a future version of a
program. The warning also includes the location of the declaration
of the deprecated variable, to enable users to easily find further
information about why the variable is deprecated, or what they should
do instead. Note that the warning only occurs for uses:
extern int old_var __attribute__ ((deprecated));
extern int old_var;
int new_fn () { return old_var; }
|
results in a warning on line 3 but not line 2.
The deprecated attribute can also be used for functions and
types (see section 5.25 Declaring Attributes of Functions, see section 5.33 Specifying Attributes of Types.)
mode (mode)
You may also specify a mode of `byte' or `__byte__' to indicate the mode corresponding to a one-byte integer, `word' or `__word__' for the mode of a one-word integer, and `pointer' or `__pointer__' for the mode used to represent pointers.
packed
packed attribute specifies that a variable or structure field
should have the smallest possible alignment--one byte for a variable,
and one bit for a field, unless you specify a larger value with the
aligned attribute.
Here is a structure in which the field x is packed, so that it
immediately follows a:
struct foo
{
char a;
int x[2] __attribute__ ((packed));
};
|
section ("section-name")
data and bss. Sometimes, however, you need additional sections,
or you need certain particular variables to appear in special sections,
for example to map to special hardware. The section
attribute specifies that a variable (or function) lives in a particular
section. For example, this small program uses several specific section names:
struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
int init_data __attribute__ ((section ("INITDATA"))) = 0;
main()
{
/* Initialize stack pointer */
init_sp (stack + sizeof (stack));
/* Initialize initialized data */
memcpy (&init_data, &data, &edata - &data);
/* Turn on the serial ports */
init_duart (&a);
init_duart (&b);
}
|
Use the section attribute with an initialized definition
of a global variable, as shown in the example. GCC issues
a warning and otherwise ignores the section attribute in
uninitialized variable declarations.
You may only use the section attribute with a fully initialized
global definition because of the way linkers work. The linker requires
each object be defined once, with the exception that uninitialized
variables tentatively go in the common (or bss) section
and can be multiply "defined". You can force a variable to be
initialized with the `-fno-common' flag or the nocommon
attribute.
Some file formats do not support arbitrary sections so the section
attribute is not available on all platforms.
If you need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.
shared
shared and marking the section
shareable:
int foo __attribute__((section ("shared"), shared)) = 0;
int
main()
{
/* Read and write foo. All running
copies see the same value. */
return 0;
}
|
You may only use the shared attribute along with section
attribute with a fully initialized global definition because of the way
linkers work. See section attribute for more information.
The shared attribute is only available on Windows.
tls_model ("tls_model")
tls_model attribute sets thread-local storage model
(see section 5.48 Thread-Local Storage) of a particular __thread variable,
overriding -ftls-model= command line switch on a per-variable
basis.
The tls_model argument should be one of global-dynamic,
local-dynamic, initial-exec or local-exec.
Not all targets support this attribute.
transparent_union
typedef for a union data type; then it
applies to all function parameters with that type.
unused
vector_size (bytes)
int foo __attribute__ ((vector_size (16))); |
causes the compiler to set the mode for foo, to be 16 bytes,
divided into int sized units. Assuming a 32-bit int (a vector of
4 units of 4 bytes), the corresponding mode of foo will be V4SI.
This attribute is only applicable to integral and float scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct.
Aggregates with this attribute are invalid, even if they are of the same size as a corresponding scalar. For example, the declaration:
struct S { int a; };
struct S __attribute__ ((vector_size (16))) foo;
|
is invalid even if the size of the structure is the same as the size of
the int.
weak
weak attribute is described in See section 5.25 Declaring Attributes of Functions.
model (model-name)
small, medium,
or large, representing each of the code models.
Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the ld24 instruction).
Medium and large model objects may live anywhere in the 32-bit address space
(the compiler will generate seth/add3 instructions to load their
addresses).
dllimport
dllimport attribute is described in See section 5.25 Declaring Attributes of Functions.
dlexport
dllexport attribute is described in See section 5.25 Declaring Attributes of Functions.
To specify multiple attributes, separate them by commas within the double parentheses: for example, `__attribute__ ((aligned (16), packed))'.
The keyword __attribute__ allows you to specify special
attributes of struct and union types when you define such
types. This keyword is followed by an attribute specification inside
double parentheses. Six attributes are currently defined for types:
aligned, packed, transparent_union, unused,
deprecated and may_alias. Other attributes are defined for
functions (see section 5.25 Declaring Attributes of Functions) and for variables
(see section 5.32 Specifying Attributes of Variables).
You may also specify any one of these attributes with `__'
preceding and following its keyword. This allows you to use these
attributes in header files without being concerned about a possible
macro of the same name. For example, you may use __aligned__
instead of aligned.
You may specify the aligned and transparent_union
attributes either in a typedef declaration or just past the
closing curly brace of a complete enum, struct or union type
definition and the packed attribute only past the closing
brace of a definition.
You may also specify attributes between the enum, struct or union tag and the name of the type rather than after the closing brace.
See section 5.26 Attribute Syntax, for details of the exact syntax for using attributes.
aligned (alignment)
struct S { short f[3]; } __attribute__ ((aligned (8)));
typedef int more_aligned_int __attribute__ ((aligned (8)));
|
force the compiler to insure (as far as it can) that each variable whose
type is struct S or more_aligned_int will be allocated and
aligned at least on a 8-byte boundary. On a SPARC, having all
variables of type struct S aligned to 8-byte boundaries allows
the compiler to use the ldd and std (doubleword load and
store) instructions when copying one variable of type struct S to
another, thus improving run-time efficiency.
Note that the alignment of any given struct or union type
is required by the ISO C standard to be at least a perfect multiple of
the lowest common multiple of the alignments of all of the members of
the struct or union in question. This means that you can
effectively adjust the alignment of a struct or union
type by attaching an aligned attribute to any one of the members
of such a type, but the notation illustrated in the example above is a
more obvious, intuitive, and readable way to request the compiler to
adjust the alignment of an entire struct or union type.
As in the preceding example, you can explicitly specify the alignment
(in bytes) that you wish the compiler to use for a given struct
or union type. Alternatively, you can leave out the alignment factor
and just ask the compiler to align a type to the maximum
useful alignment for the target machine you are compiling for. For
example, you could write:
struct S { short f[3]; } __attribute__ ((aligned));
|
Whenever you leave out the alignment factor in an aligned
attribute specification, the compiler automatically sets the alignment
for the type to the largest alignment which is ever used for any data
type on the target machine you are compiling for. Doing this can often
make copy operations more efficient, because the compiler can use
whatever instructions copy the biggest chunks of memory when performing
copies to or from the variables which have types that you have aligned
this way.
In the example above, if the size of each short is 2 bytes, then
the size of the entire struct S type is 6 bytes. The smallest
power of two which is greater than or equal to that is 8, so the
compiler sets the alignment for the entire struct S type to 8
bytes.
Note that although you can ask the compiler to select a time-efficient alignment for a given type and then declare only individual stand-alone objects of that type, the compiler's ability to select a time-efficient alignment is primarily useful only when you plan to create arrays of variables having the relevant (efficiently aligned) type. If you declare or use arrays of variables of an efficiently-aligned type, then it is likely that your program will also be doing pointer arithmetic (or subscripting, which amounts to the same thing) on pointers to the relevant type, and the code that the compiler generates for these pointer arithmetic operations will often be more efficient for efficiently-aligned types than for other types.
The aligned attribute can only increase the alignment; but you
can decrease it by specifying packed as well. See below.
Note that the effectiveness of aligned attributes may be limited
by inherent limitations in your linker. On many systems, the linker is
only able to arrange for variables to be aligned up to a certain maximum
alignment. (For some linkers, the maximum supported alignment may
be very very small.) If your linker is only able to align variables
up to a maximum of 8 byte alignment, then specifying aligned(16)
in an __attribute__ will still only provide you with 8 byte
alignment. See your linker documentation for further information.
packed
enum, struct, or
union type definition, specifies that the minimum required memory
be used to represent the type.
Specifying this attribute for struct and union types is
equivalent to specifying the packed attribute on each of the
structure or union members. Specifying the `-fshort-enums'
flag on the line is equivalent to specifying the packed
attribute on all enum definitions.
You may only specify this attribute after a closing curly brace on an
enum definition, not in a typedef declaration, unless that
declaration also contains the definition of the enum.
transparent_union
union type definition, indicates
that any function parameter having that union type causes calls to that
function to be treated in a special way.
First, the argument corresponding to a transparent union type can be of
any type in the union; no cast is required. Also, if the union contains
a pointer type, the corresponding argument can be a null pointer
constant or a void pointer expression; and if the union contains a void
pointer type, the corresponding argument can be any pointer expression.
If the union member type is a pointer, qualifiers like const on
the referenced type must be respected, just as with normal pointer
conversions.
Second, the argument is passed to the function using the calling conventions of the first member of the transparent union, not the calling conventions of the union itself. All members of the union must have the same machine representation; this is necessary for this argument passing to work properly.
Transparent unions are designed for library functions that have multiple
interfaces for compatibility reasons. For example, suppose the
wait function must accept either a value of type int * to
comply with Posix, or a value of type union wait * to comply with
the 4.1BSD interface. If wait's parameter were void *,
wait would accept both kinds of arguments, but it would also
accept any other pointer type and this would make argument type checking
less useful. Instead, <sys/wait.h> might define the interface
as follows:
typedef union
{
int *__ip;
union wait *__up;
} wait_status_ptr_t __attribute__ ((__transparent_union__));
pid_t wait (wait_status_ptr_t);
|
This interface allows either int * or union wait *
arguments to be passed, using the int * calling convention.
The program can call wait with arguments of either type:
int w1 () { int w; return wait (&w); }
int w2 () { union wait w; return wait (&w); }
|
With this interface, wait's implementation might look like this:
pid_t wait (wait_status_ptr_t p)
{
return waitpid (-1, p.__ip, 0);
}
|
unused
union or a struct),
this attribute means that variables of that type are meant to appear
possibly unused. GCC will not produce a warning for any variables of
that type, even if the variable appears to do nothing. This is often
the case with lock or thread classes, which are usually defined and then
not referenced, but contain constructors and destructors that have
nontrivial bookkeeping functions.
deprecated
deprecated attribute results in a warning if the type
is used anywhere in the source file. This is useful when identifying
types that are expected to be removed in a future version of a program.
If possible, the warning also includes the location of the declaration
of the deprecated type, to enable users to easily find further
information about why the type is deprecated, or what they should do
instead. Note that the warnings only occur for uses and then only
if the type is being applied to an identifier that itself is not being
declared as deprecated.
typedef int T1 __attribute__ ((deprecated)); T1 x; typedef T1 T2; T2 y; typedef T1 T3 __attribute__ ((deprecated)); T3 z __attribute__ ((deprecated)); |
results in a warning on line 2 and 3 but not lines 4, 5, or 6. No warning is issued for line 4 because T2 is not explicitly deprecated. Line 5 has no warning because T3 is explicitly deprecated. Similarly for line 6.
The deprecated attribute can also be used for functions and
variables (see section 5.25 Declaring Attributes of Functions, see section 5.32 Specifying Attributes of Variables.)
may_alias
char type. See
`-fstrict-aliasing' for more information on aliasing issues.
Example of use:
typedef short __attribute__((__may_alias__)) short_a;
int
main (void)
{
int a = 0x12345678;
short_a *b = (short_a *) &a;
b[1] = 0;
if (a == 0x12345678)
abort();
exit(0);
}
|
If you replaced short_a with short in the variable
declaration, the above program would abort when compiled with
`-fstrict-aliasing', which is on by default at `-O2' or
above in recent GCC versions.
To specify multiple attributes, separate them by commas within the double parentheses: for example, `__attribute__ ((aligned (16), packed))'.
By declaring a function inline, you can direct GCC to
integrate that function's code into the code for its callers. This
makes execution faster by eliminating the function-call overhead; in
addition, if any of the actual argument values are constant, their known
values may permit simplifications at compile time so that not all of the
inline function's code needs to be included. The effect on code size is
less predictable; object code may be larger or smaller with function
inlining, depending on the particular case. Inlining of functions is an
optimization and it really "works" only in optimizing compilation. If
you don't use `-O', no function is really inline.
Inline functions are included in the ISO C99 standard, but there are currently substantial differences between what GCC implements and what the ISO C99 standard requires.
To declare a function inline, use the inline keyword in its
declaration, like this:
inline int
inc (int *a)
{
(*a)++;
}
|
(If you are writing a header file to be included in ISO C programs, write
__inline__ instead of inline. See section 5.39 Alternate Keywords.)
You can also make all "simple enough" functions inline with the option
`-finline-functions'.
Note that certain usages in a function definition can make it unsuitable
for inline substitution. Among these usages are: use of varargs, use of
alloca, use of variable sized data types (see section 5.14 Arrays of Variable Length),
use of computed goto (see section 5.3 Labels as Values), use of nonlocal goto,
and nested functions (see section 5.4 Nested Functions). Using `-Winline'
will warn when a function marked inline could not be substituted,
and will give the reason for the failure.
Note that in C and Objective-C, unlike C++, the inline keyword
does not affect the linkage of the function.
GCC automatically inlines member functions defined within the class
body of C++ programs even if they are not explicitly declared
inline. (You can override this with `-fno-default-inline';
see section Options Controlling C++ Dialect.)
When a function is both inline and static, if all calls to the
function are integrated into the caller, and the function's address is
never used, then the function's own assembler code is never referenced.
In this case, GCC does not actually output assembler code for the
function, unless you specify the option `-fkeep-inline-functions'.
Some calls cannot be integrated for various reasons (in particular,
calls that precede the function's definition cannot be integrated, and
neither can recursive calls within the definition). If there is a
nonintegrated call, then the function is compiled to assembler code as
usual. The function must also be compiled as usual if the program
refers to its address, because that can't be inlined.
When an inline function is not static, then the compiler must assume
that there may be calls from other source files; since a global symbol can
be defined only once in any program, the function must not be defined in
the other source files, so the calls therein cannot be integrated.
Therefore, a non-static inline function is always compiled on its
own in the usual fashion.
If you specify both inline and extern in the function
definition, then the definition is used only for inlining. In no case
is the function compiled on its own, not even if you refer to its
address explicitly. Such an address becomes an external reference, as
if you had only declared the function, and had not defined it.
This combination of inline and extern has almost the
effect of a macro. The way to use it is to put a function definition in
a header file with these keywords, and put another copy of the
definition (lacking inline and extern) in a library file.
The definition in the header file will cause most calls to the function
to be inlined. If any uses of the function remain, they will refer to
the single copy in the library.
Since GCC eventually will implement ISO C99 semantics for
inline functions, it is best to use static inline only
to guarantee compatibility. (The
existing semantics will remain available when `-std=gnu89' is
specified, but eventually the default will be `-std=gnu99' and
that will implement the C99 semantics, though it does not do so yet.)
GCC does not inline any functions when not optimizing unless you specify the `always_inline' attribute for the function, like this:
/* Prototype. */ inline void foo (const char) __attribute__((always_inline)); |
In an assembler instruction using asm, you can specify the
operands of the instruction using C expressions. This means you need not
guess which registers or memory locations will contain the data you want
to use.
You must specify an assembler instruction template much like what appears in a machine description, plus an operand constraint string for each operand.
For example, here is how to use the 68881's fsinx instruction:
asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
|
Here angle is the C expression for the input operand while
result is that of the output operand. Each has `"f"' as its
operand constraint, saying that a floating point register is required.
The `=' in `=f' indicates that the operand is an output; all
output operands' constraints must use `='. The constraints use the
same language used in the machine description (see section 5.36 Constraints for asm Operands).
Each operand is described by an operand-constraint string followed by the C expression in parentheses. A colon separates the assembler template from the first output operand and another separates the last output operand from the first input, if any. Commas separate the operands within each group. The total number of operands is currently limited to 30; this limitation may be lifted in some future version of GCC.
If there are no output operands but there are input operands, you must place two consecutive colons surrounding the place where the output operands would go.
As of GCC version 3.1, it is also possible to specify input and output
operands using symbolic names which can be referenced within the
assembler code. These names are specified inside square brackets
preceding the constraint string, and can be referenced inside the
assembler code using %[name] instead of a percentage sign
followed by the operand number. Using named operands the above example
could look like:
asm ("fsinx %[angle],%[output]"
: [output] "=f" (result)
: [angle] "f" (angle));
|
Note that the symbolic operand names have no relation whatsoever to other C identifiers. You may use any name you like, even those of existing C symbols, but you must ensure that no two operands within the same assembler construct use the same symbolic name.
Output operand expressions must be lvalues; the compiler can check this.
The input operands need not be lvalues. The compiler cannot check
whether the operands have data types that are reasonable for the
instruction being executed. It does not parse the assembler instruction
template and does not know what it means or even whether it is valid
assembler input. The extended asm feature is most often used for
machine instructions the compiler itself does not know exist. If
the output expression cannot be directly addressed (for example, it is a
bit-field), your constraint must allow a register. In that case, GCC
will use the register as the output of the asm, and then store
that register into the output.
The ordinary output operands must be write-only; GCC will assume that the values in these operands before the instruction are dead and need not be generated. Extended asm supports input-output or read-write operands. Use the constraint character `+' to indicate such an operand and list it with the output operands.
When the constraints for the read-write operand (or the operand in which
only some of the bits are to be changed) allows a register, you may, as
an alternative, logically split its function into two separate operands,
one input operand and one write-only output operand. The connection
between them is expressed by constraints which say they need to be in
the same location when the instruction executes. You can use the same C
expression for both operands, or different expressions. For example,
here we write the (fictitious) `combine' instruction with
bar as its read-only source operand and foo as its
read-write destination:
asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));
|
The constraint `"0"' for operand 1 says that it must occupy the same location as operand 0. A number in constraint is allowed only in an input operand and it must refer to an output operand.
Only a number in the constraint can guarantee that one operand will be in
the same place as another. The mere fact that foo is the value
of both operands is not enough to guarantee that they will be in the
same place in the generated assembler code. The following would not
work reliably:
asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));
|
Various optimizations or reloading could cause operands 0 and 1 to be in
different registers; GCC knows no reason not to do so. For example, the
compiler might find a copy of the value of foo in one register and
use it for operand 1, but generate the output operand 0 in a different
register (copying it afterward to foo's own address). Of course,
since the register for operand 1 is not even mentioned in the assembler
code, the result will not work, but GCC can't tell that.
As of GCC version 3.1, one may write [name] instead of
the operand number for a matching constraint. For example:
asm ("cmoveq %1,%2,%[result]"
: [result] "=r"(result)
: "r" (test), "r"(new), "[result]"(old));
|
Some instructions clobber specific hard registers. To describe this, write a third colon after the input operands, followed by the names of the clobbered hard registers (given as strings). Here is a realistic example for the VAX:
asm volatile ("movc3 %0,%1,%2"
: /* no outputs */
: "g" (from), "g" (to), "g" (count)
: "r0", "r1", "r2", "r3", "r4", "r5");
|
You may not write a clobber description in a way that overlaps with an
input or output operand. For example, you may not have an operand
describing a register class with one member if you mention that register
in the clobber list. Variables declared to live in specific registers
(see section 5.38 Variables in Specified Registers), and used as asm input or output operands must
have no part mentioned in the clobber description.
There is no way for you to specify that an input
operand is modified without also specifying it as an output
operand. Note that if all the output operands you specify are for this
purpose (and hence unused), you will then also need to specify
volatile for the asm construct, as described below, to
prevent GCC from deleting the asm statement as unused.
If you refer to a particular hardware register from the assembler code, you will probably have to list the register after the third colon to tell the compiler the register's value is modified. In some assemblers, the register names begin with `%'; to produce one `%' in the assembler code, you must write `%%' in the input.
If your assembler instruction can alter the condition code register, add `cc' to the list of clobbered registers. GCC on some machines represents the condition codes as a specific hardware register; `cc' serves to name this register. On other machines, the condition code is handled differently, and specifying `cc' has no effect. But it is valid no matter what the machine.
If your assembler instructions access memory in an unpredictable
fashion, add `memory' to the list of clobbered registers. This
will cause GCC to not keep memory values cached in registers across the
assembler instruction and not optimize stores or loads to that memory.
You will also want to add the volatile keyword if the memory
affected is not listed in the inputs or outputs of the asm, as
the `memory' clobber does not count as a side-effect of the
asm. If you know how large the accessed memory is, you can add
it as input or output but if this is not known, you should add
`memory'. As an example, if you access ten bytes of a string, you
can use a memory input like:
{"m"( ({ struct { char x[10]; } *p = (void *)ptr ; *p; }) )}.
|
Note that in the following example the memory input is necessary,
otherwise GCC might optimize the store to x away:
int foo ()
{
int x = 42;
int *y = &x;
int result;
asm ("magic stuff accessing an 'int' pointed to by '%1'"
"=&d" (r) : "a" (y), "m" (*y));
return result;
}
|
You can put multiple assembler instructions together in a single
asm template, separated by the characters normally used in assembly
code for the system. A combination that works in most places is a newline
to break the line, plus a tab character to move to the instruction field
(written as `\n\t'). Sometimes semicolons can be used, if the
assembler allows semicolons as a line-breaking character. Note that some
assembler dialects use semicolons to start a comment.
The input operands are guaranteed not to use any of the clobbered
registers, and neither will the output operands' addresses, so you can
read and write the clobbered registers as many times as you like. Here
is an example of multiple instructions in a template; it assumes the
subroutine _foo accepts arguments in registers 9 and 10:
asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo"
: /* no outputs */
: "g" (from), "g" (to)
: "r9", "r10");
|
Unless an output operand has the `&' constraint modifier, GCC may allocate it in the same register as an unrelated input operand, on the assumption the inputs are consumed before the outputs are produced. This assumption may be false if the assembler code actually consists of more than one instruction. In such a case, use `&' for each output operand that may not overlap an input. See section 5.36.3 Constraint Modifier Characters.
If you want to test the condition code produced by an assembler
instruction, you must include a branch and a label in the asm
construct, as follows:
asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:"
: "g" (result)
: "g" (input));
|
This assumes your assembler supports local labels, as the GNU assembler and most Unix assemblers do.
Speaking of labels, jumps from one asm to another are not
supported. The compiler's optimizers do not know about these jumps, and
therefore they cannot take account of them when deciding how to
optimize.
Usually the most convenient way to use these asm instructions is to
encapsulate them in macros that look like functions. For example,
#define sin(x) \
({ double __value, __arg = (x); \
asm ("fsinx %1,%0": "=f" (__value): "f" (__arg)); \
__value; })
|
Here the variable __arg is used to make sure that the instruction
operates on a proper double value, and to accept only those
arguments x which can convert automatically to a double.
Another way to make sure the instruction operates on the correct data
type is to use a cast in the asm. This is different from using a
variable __arg in that it converts more different types. For
example, if the desired type were int, casting the argument to
int would accept a pointer with no complaint, while assigning the
argument to an int variable named __arg would warn about
using a pointer unless the caller explicitly casts it.
If an asm has output operands, GCC assumes for optimization
purposes the instruction has no side effects except to change the output
operands. This does not mean instructions with a side effect cannot be
used, but you must be careful, because the compiler may eliminate them
if the output operands aren't used, or move them out of loops, or
replace two with one if they constitute a common subexpression. Also,
if your instruction does have a side effect on a variable that otherwise
appears not to change, the old value of the variable may be reused later
if it happens to be found in a register.
You can prevent an asm instruction from being deleted, moved
significantly, or combined, by writing the keyword volatile after
the asm. For example:
#define get_and_set_priority(new) \
({ int __old; \
asm volatile ("get_and_set_priority %0, %1" \
: "=g" (__old) : "g" (new)); \
__old; })
|
If you write an asm instruction with no outputs, GCC will know
the instruction has side-effects and will not delete the instruction or
move it outside of loops.
The volatile keyword indicates that the instruction has
important side-effects. GCC will not delete a volatile asm if
it is reachable. (The instruction can still be deleted if GCC can
prove that control-flow will never reach the location of the
instruction.) In addition, GCC will not reschedule instructions
across a volatile asm instruction. For example:
*(volatile int *)addr = foo;
asm volatile ("eieio" : : );
|
Assume addr contains the address of a memory mapped device
register. The PowerPC eieio instruction (Enforce In-order
Execution of I/O) tells the CPU to make sure that the store to that
device register happens before it issues any other I/O.
Note that even a volatile asm instruction can be moved in ways
that appear insignificant to the compiler, such as across jump
instructions. You can't expect a sequence of volatile asm
instructions to remain perfectly consecutive. If you want consecutive
output, use a single asm. Also, GCC will perform some
optimizations across a volatile asm instruction; GCC does not
"forget everything" when it encounters a volatile asm
instruction the way some other compilers do.
An asm instruction without any operands or clobbers (an "old
style" asm) will be treated identically to a volatile
asm instruction.
It is a natural idea to look for a way to give access to the condition code left by the assembler instruction. However, when we attempted to implement this, we found no way to make it work reliably. The problem is that output operands might need reloading, which would result in additional following "store" instructions. On most machines, these instructions would alter the condition code before there was time to test it. This problem doesn't arise for ordinary "test" and "compare" instructions because they don't have any output operands.
For reasons similar to those described above, it is not possible to give an assembler instruction access to the condition code left by previous instructions.
If you are writing a header file that should be includable in ISO C
programs, write __asm__ instead of asm. See section 5.39 Alternate Keywords.
There are several rules on the usage of stack-like regs in asm_operands insns. These rules apply only to the operands that are stack-like regs:
An input reg that is implicitly popped by the asm must be explicitly clobbered, unless it is constrained to match an output operand.
All implicitly popped input regs must be closer to the top of the reg-stack than any input that is not implicitly popped.
It is possible that if an input dies in an insn, reload might use the input reg for an output reload. Consider this example:
asm ("foo" : "=t" (a) : "f" (b));
|
This asm says that input B is not popped by the asm, and that the asm pushes a result onto the reg-stack, i.e., the stack is one deeper after the asm than it was before. But, it is possible that reload will think that it can use the same reg for both the input and the output, if input B dies in this insn.
If any input operand uses the f constraint, all output reg
constraints must use the & earlyclobber.
The asm above would be written as
asm ("foo" : "=&t" (a) : "f" (b));
|
Output operands must specifically indicate which reg an output
appears in after an asm. =f is not allowed: the operand
constraints must select a class with a single reg.
Output operands must start at the top of the reg-stack: output operands may not "skip" a reg.
Here are a couple of reasonable asms to want to write. This asm takes one input, which is internally popped, and produces two outputs.
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));
|
This asm takes two inputs, which are popped by the fyl2xp1 opcode,
and replaces them with one output. The user must code the st(1)
clobber for reg-stack.c to know that fyl2xp1 pops both inputs.
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");
|
asm Operands
Here are specific details on what constraint letters you can use with
asm operands.
Constraints can say whether
an operand may be in a register, and which kinds of register; whether the
operand can be a memory reference, and which kinds of address; whether the
operand may be an immediate constant, and which possible values it may
have. Constraints can also require two operands to match.
5.36.1 Simple Constraints Basic use of constraints. 5.36.2 Multiple Alternative Constraints When an insn has two alternative constraint-patterns. 5.36.3 Constraint Modifier Characters More precise control over effects of constraints. 5.36.4 Constraints for Particular Machines Special constraints for some particular machines.
The simplest kind of constraint is a string full of letters, each of which describes one kind of operand that is permitted. Here are the letters that are allowed:
For example, an address which is constant is offsettable; so is an address that is the sum of a register and a constant (as long as a slightly larger constant is also within the range of address-offsets supported by the machine); but an autoincrement or autodecrement address is not offsettable. More complicated indirect/indexed addresses may or may not be offsettable depending on the other addressing modes that the machine supports.
Note that in an output operand which can be matched by another operand, the constraint letter `o' is valid only when accompanied by both `<' (if the target machine has predecrement addressing) and `>' (if the target machine has preincrement addressing).
const_double) is
allowed, but only if the target floating point format is the same as
that of the host machine (on which the compiler is running).
const_double or
const_vector) is allowed.
This might appear strange; if an insn allows a constant operand with a value not known at compile time, it certainly must allow any known value. So why use `s' instead of `i'? Sometimes it allows better code to be generated.
For example, on the 68000 in a fullword instruction it is possible to use an immediate operand; but if the immediate value is between -128 and 127, better code results from loading the value into a register and using the register. This is because the load into the register can be done with a `moveq' instruction. We arrange for this to happen by defining the letter `K' to mean "any integer outside the range -128 to 127", and then specifying `Ks' in the operand constraints.
This number is allowed to be more than a single digit. If multiple digits are encountered consecutively, they are interpreted as a single decimal integer. There is scant chance for ambiguity, since to-date it has never been desirable that `10' be interpreted as matching either operand 1 or operand 0. Should this be desired, one can use multiple alternatives instead.
This is called a matching constraint and what it really means is
that the assembler has only a single operand that fills two roles
which asm distinguishes. For example, an add instruction uses
two input operands and an output operand, but on most CISC
machines an add instruction really has only two operands, one of them an
input-output operand:
addl #35,r12 |
Matching constraints are used in these circumstances. More precisely, the two operands that match must include one input-only operand and one output-only operand. Moreover, the digit must be a smaller number than the number of the operand that uses it in the constraint.
`p' in the constraint must be accompanied by address_operand
as the predicate in the match_operand. This predicate interprets
the mode specified in the match_operand as the mode of the memory
reference for which the address would be valid.
Sometimes a single instruction has multiple alternative sets of possible operands. For example, on the 68000, a logical-or instruction can combine register or an immediate value into memory, or it can combine any kind of operand into a register; but it cannot combine one memory location into another.
These constraints are represented as multiple alternatives. An alternative can be described by a series of letters for each operand. The overall constraint for an operand is made from the letters for this operand from the first alternative, a comma, the letters for this operand from the second alternative, a comma, and so on until the last alternative.
If all the operands fit any one alternative, the instruction is valid. Otherwise, for each alternative, the compiler counts how many instructions must be added to copy the operands so that that alternative applies. The alternative requiring the least copying is chosen. If two alternatives need the same amount of copying, the one that comes first is chosen. These choices can be altered with the `?' and `!' characters:
?
!
Here are constraint modifier characters.
When the compiler fixes up the operands to satisfy the constraints, it needs to know which operands are inputs to the instruction and which are outputs from it. `=' identifies an output; `+' identifies an operand that is both input and output; all other operands are assumed to be input only.
If you specify `=' or `+' in a constraint, you put it in the first character of the constraint string.
`&' applies only to the alternative in which it is written. In constraints with multiple alternatives, sometimes one alternative requires `&' while others do not. See, for example, the `movdf' insn of the 68000.
An input operand can be tied to an earlyclobber operand if its only use as an input occurs before the early result is written. Adding alternatives of this form often allows GCC to produce better code when only some of the inputs can be affected by the earlyclobber. See, for example, the `mulsi3' insn of the ARM.
`&' does not obviate the need to write `='.
Whenever possible, you should use the general-purpose constraint letters
in asm arguments, since they will convey meaning more readily to
people reading your code. Failing that, use the constraint letters
that usually have very similar meanings across architectures. The most
commonly used constraints are `m' and `r' (for memory and
general-purpose registers respectively; see section 5.36.1 Simple Constraints), and
`I', usually the letter indicating the most common
immediate-constant format.
For each machine architecture, the
`config/machine/machine.h' file defines additional
constraints. These constraints are used by the compiler itself for
instruction generation, as well as for asm statements; therefore,
some of the constraints are not particularly interesting for asm.
The constraints are defined through these macros:
REG_CLASS_FROM_LETTER
CONST_OK_FOR_LETTER_P
CONST_DOUBLE_OK_FOR_LETTER_P
EXTRA_CONSTRAINT
Inspecting these macro definitions in the compiler source for your machine is the best way to be certain you have the right constraints. However, here is a summary of the machine-dependent constraints available on some particular machines.
f
F
G
I
J
K
L
M
Q
asm statements)
R
S
l
a
d
w
e
b
q
t
x
y
z
I
J
K
L
M
N
O
P
G
b
f
h
q
c
l
x
y
z
I
J
SImode constants)
K
L
M
N
O
P
G
Q
asm statements)
R
S
T
U
q
b, c, or d register for the i386.
For x86-64 it is equivalent to `r' class. (for 8-bit instructions that
do not use upper halves)
Q
b, c, or d register. (for 8-bit instructions,
that do use upper halves)
R
r class in i386 mode.
(for non-8-bit registers used together with 8-bit upper halves in a single
instruction)
A
f
t
u
a
b
c
C
d
D
S
x
y
I
J
K
L
M
lea instruction)
N
out instruction)
Z
0xffffffff or symbolic reference known to fit specified range.
(for using immediates in zero extending 32-bit to 64-bit x86-64 instructions)
e
G
f
fp0 to fp3)
l
r0 to r15)
b
g0 to g15)
d
I
J
K
G
H
a
r0 to r3 for addl instruction
b
c
d
e
f
m
G
I
J
K
L
M
N
O
P
dep instruction
Q
R
shladd instruction
S
a
ACC_REGS (acc0 to acc7).
b
EVEN_ACC_REGS (acc0 to acc7).
c
CC_REGS (fcc0 to fcc3 and
icc0 to icc3).
d
GPR_REGS (gr0 to gr63).
e
EVEN_REGS (gr0 to gr63).
Odd registers are excluded not in the class but through the use of a machine
mode larger than 4 bytes.
f
FPR_REGS (fr0 to fr63).
h
FEVEN_REGS (fr0 to fr63).
Odd registers are excluded not in the class but through the use of a machine
mode larger than 4 bytes.
l
LR_REG (the lr register).
q
QUAD_REGS (gr2 to gr63).
Register numbers not divisible by 4 are excluded not in the class but through
the use of a machine mode larger than 8 bytes.
t
ICC_REGS (icc0 to icc3).
u
FCC_REGS (fcc0 to fcc3).
v
ICR_REGS (cc4 to cc7).
w
FCR_REGS (cc0 to cc3).
x
QUAD_FPR_REGS (fr0 to fr63).
Register numbers not divisible by 4 are excluded not in the class but through
the use of a machine mode larger than 8 bytes.
z
SPR_REGS (lcr and lr).
A
QUAD_ACC_REGS (acc0 to acc7).
B
ACCG_REGS (accg0 to accg7).
C
CR_REGS (cc0 to cc7).
G
I
J
L
M
N
O
P
a
f
j
k
b
y
z
q
c
d
u
R
QImode, since we
can't access extra bytes
S
T
I
J
K
L
M
N
O
P
d
f
h
l
x
y
z
I
J
K
L
lui)
M
N
O
P
G
Q
asm statements)
R
asm statements)
S
asm statements)
a
d
f
x
y
I
J
K
L
M
G
H
a
b
d
q
t
u
w
x
y
z
A
B
D
L
M
N
O
P
f
e
c
d
b
h
I
J
K
sethi instruction)
L
movcc instructions
M
movrcc instructions
N
SImode
O
G
H
Q
R
S
T
U
W
a
b
c
f
k
q
t
u
v
x
y
z
G
H
I
J
K
L
M
N
O
Q
R
S
T
U
a
d
f
I
J
K
L
Q
S
larl instruction
a
b
c
d
e
t
y
z
I
J
K
L
M
N
O
P
Q
R
S
T
U
a
b
A
I
J
K
L
You can specify the name to be used in the assembler code for a C
function or variable by writing the asm (or __asm__)
keyword after the declarator as follows:
int foo asm ("myfoo") = 2;
|
This specifies that the name to be used for the variable foo in
the assembler code should be `myfoo' rather than the usual
`_foo'.
On systems where an underscore is normally prepended to the name of a C function or variable, this feature allows you to define names for the linker that do not start with an underscore.
It does not make sense to use this feature with a non-static local variable since such variables do not have assembler names. If you are trying to put the variable in a particular register, see 5.38 Variables in Specified Registers. GCC presently accepts such code with a warning, but will probably be changed to issue an error, rather than a warning, in the future.
You cannot use asm in this way in a function definition; but
you can get the same effect by writing a declaration for the function
before its definition and putting asm there, like this:
extern func () asm ("FUNC");
func (x, y)
int x, y;
/* ... */
|
It is up to you to make sure that the assembler names you choose do not conflict with any other assembler symbols. Also, you must not use a register name; that would produce completely invalid assembler code. GCC does not as yet have the ability to store static variables in registers. Perhaps that will be added.
GNU C allows you to put a few global variables into specified hardware registers. You can also specify the register in which an ordinary register variable should be allocated.
These local variables are sometimes convenient for use with the extended
asm feature (see section 5.35 Assembler Instructions with C Expression Operands), if you want to write one
output of the assembler instruction directly into a particular register.
(This will work provided the register you specify fits the constraints
specified for that operand in the asm.)
5.38.1 Defining Global Register Variables 5.38.2 Specifying Registers for Local Variables
You can define a global register variable in GNU C like this:
register int *foo asm ("a5");
|
Here a5 is the name of the register which should be used. Choose a
register which is normally saved and restored by function calls on your
machine, so that library routines will not clobber it.
Naturally the register name is cpu-dependent, so you would need to
conditionalize your program according to cpu type. The register
a5 would be a good choice on a 68000 for a variable of pointer
type. On machines with register windows, be sure to choose a "global"
register that is not affected magically by the function call mechanism.
In addition, operating systems on one type of cpu may differ in how they
name the registers; then you would need additional conditionals. For
example, some 68000 operating systems call this register %a5.
Eventually there may be a way of asking the compiler to choose a register automatically, but first we need to figure out how it should choose and how to enable you to guide the choice. No solution is evident.
Defining a global register variable in a certain register reserves that register entirely for this use, at least within the current compilation. The register will not be allocated for any other purpose in the functions in the current compilation. The register will not be saved and restored by these functions. Stores into this register are never deleted even if they would appear to be dead, but references may be deleted or moved or simplified.
It is not safe to access the global register variables from signal handlers, or from more than one thread of control, because the system library routines may temporarily use the register for other things (unless you recompile them specially for the task at hand).
It is not safe for one function that uses a global register variable to
call another such function foo by way of a third function
lose that was compiled without knowledge of this variable (i.e. in a
different source file in which the variable wasn't declared). This is
because lose might save the register and put some other value there.
For example, you can't expect a global register variable to be available in
the comparison-function that you pass to qsort, since qsort
might have put something else in that register. (If you are prepared to
recompile qsort with the same global register variable, you can
solve this problem.)
If you want to recompile qsort or other source files which do not
actually use your global register variable, so that they will not use that
register for any other purpose, then it suffices to specify the compiler
option `-ffixed-reg'. You need not actually add a global
register declaration to their source code.
A function which can alter the value of a global register variable cannot safely be called from a function compiled without this variable, because it could clobber the value the caller expects to find there on return. Therefore, the function which is the entry point into the part of the program that uses the global register variable must explicitly save and restore the value which belongs to its caller.
On most machines, longjmp will restore to each global register
variable the value it had at the time of the setjmp. On some
machines, however, longjmp will not change the value of global
register variables. To be portable, the function that called setjmp
should make other arrangements to save the values of the global register
variables, and to restore them in a longjmp. This way, the same
thing will happen regardless of what longjmp does.
All global register variable declarations must precede all function definitions. If such a declaration could appear after function definitions, the declaration would be too late to prevent the register from being used for other purposes in the preceding functions.
Global register variables may not have initial values, because an executable file has no means to supply initial contents for a register.
On the SPARC, there are reports that g3 ... g7 are suitable
registers, but certain library functions, such as getwd, as well
as the subroutines for division and remainder, modify g3 and g4. g1 and
g2 are local temporaries.
On the 68000, a2 ... a5 should be suitable, as should d2 ... d7. Of course, it will not do to use more than a few of those.
You can define a local register variable with a specified register like this:
register int *foo asm ("a5");
|
Here a5 is the name of the register which should be used. Note
that this is the same syntax used for defining global register
variables, but for a local variable it would appear within a function.
Naturally the register name is cpu-dependent, but this is not a problem, since specific registers are most often useful with explicit assembler instructions (see section 5.35 Assembler Instructions with C Expression Operands). Both of these things generally require that you conditionalize your program according to cpu type.
In addition, operating systems on one type of cpu may differ in how they
name the registers; then you would need additional conditionals. For
example, some 68000 operating systems call this register %a5.
Defining such a register variable does not reserve the register; it remains available for other uses in places where flow control determines the variable's value is not live. However, these registers are made unavailable for use in the reload pass; excessive use of this feature leaves the compiler too few available registers to compile certain functions.
This option does not guarantee that GCC will generate code that has
this variable in the register you specify at all times. You may not
code an explicit reference to this register in an asm statement
and assume it will always refer to this variable.
Stores into local register variables may be deleted when they appear to be dead according to dataflow analysis. References to local register variables may be deleted or moved or simplified.
`-ansi' and the various `-std' options disable certain
keywords. This causes trouble when you want to use GNU C extensions, or
a general-purpose header file that should be usable by all programs,
including ISO C programs. The keywords asm, typeof and
inline are not available in programs compiled with
`-ansi' or `-std' (although inline can be used in a
program compiled with `-std=c99'). The ISO C99 keyword
restrict is only available when `-std=gnu99' (which will
eventually be the default) or `-std=c99' (or the equivalent
`-std=iso9899:1999') is used.
The way to solve these problems is to put `__' at the beginning and
end of each problematical keyword. For example, use __asm__
instead of asm, and __inline__ instead of inline.
Other C compilers won't accept these alternative keywords; if you want to compile with another compiler, you can define the alternate keywords as macros to replace them with the customary keywords. It looks like this:
#ifndef __GNUC__ #define __asm__ asm #endif |
`-pedantic' and other options cause warnings for many GNU C extensions.
You can
prevent such warnings within one expression by writing
__extension__ before the expression. __extension__ has no
effect aside from this.
enum Types
You can define an enum tag without specifying its possible values.
This results in an incomplete type, much like what you get if you write
struct foo without describing the elements. A later declaration
which does specify the possible values completes the type.
You can't allocate variables or storage using the type while it is incomplete. However, you can work with pointers to that type.
This extension may not be very useful, but it makes the handling of
enum more consistent with the way struct and union
are handled.
This extension is not supported by GNU C++.
GCC predefines two magic identifiers to hold the name of the current
function. The identifier __FUNCTION__ holds the name of the function
as it appears in the source. The identifier __PRETTY_FUNCTION__
holds the name of the function pretty printed in a language specific
fashion.
These names are always the same in a C function, but in a C++ function they may be different. For example, this program:
extern "C" {
extern int printf (char *, ...);
}
class a {
public:
sub (int i)
{
printf ("__FUNCTION__ = %s\n", __FUNCTION__);
printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
}
};
int
main (void)
{
a ax;
ax.sub (0);
return 0;
}
|
gives this output:
__FUNCTION__ = sub __PRETTY_FUNCTION__ = int a::sub (int) |
The compiler automagically replaces the identifiers with a string
literal containing the appropriate name. Thus, they are neither
preprocessor macros, like __FILE__ and __LINE__, nor
variables. This means that they catenate with other string literals, and
that they can be used to initialize char arrays. For example
char here[] = "Function " __FUNCTION__ " in " __FILE__; |
On the other hand, `#ifdef __FUNCTION__' does not have any special
meaning inside a function, since the preprocessor does not do anything
special with the identifier __FUNCTION__.
Note that these semantics are deprecated, and that GCC 3.2 will handle
__FUNCTION__ and __PRETTY_FUNCTION__ the same way as
__func__. __func__ is defined by the ISO standard C99:
The identifier
appeared, where function-name is the name of the lexically-enclosing function. This name is the unadorned name of the function. |
By this definition, __func__ is a variable, not a string literal.
In particular, __func__ does not catenate with other string
literals.
In C++, __FUNCTION__ and __PRETTY_FUNCTION__ are
variables, declared in the same way as __func__.
These functions may be used to get information about the callers of a function.
0 yields the return address
of the current function, a value of 1 yields the return address
of the caller of the current function, and so forth. When inlining
the expected behavior is that the function will return the address of
the function that will be returned to. To work around this behavior use
the noinline function attribute.
The level argument must be a constant integer.
On some machines it may be impossible to determine the return address of
any function other than the current one; in such cases, or when the top
of the stack has been reached, this function will return 0 or a
random value. In addition, __builtin_frame_address may be used
to determine if the top of the stack has been reached.
This function should only be used with a nonzero argument for debugging purposes.
__builtin_return_address, but it
returns the address of the function frame rather than the return address
of the function. Calling __builtin_frame_address with a value of
0 yields the frame address of the current function, a value of
1 yields the frame address of the caller of the current function,
and so forth.
The frame is the area on the stack which holds local variables and saved
registers. The frame address is normally the address of the first word
pushed on to the stack by the function. However, the exact definition
depends upon the processor and the calling convention. If the processor
has a dedicated frame pointer register, and the function has a frame,
then __builtin_frame_address will return the value of the frame
pointer register.
On some machines it may be impossible to determine the frame address of
any function other than the current one; in such cases, or when the top
of the stack has been reached, this function will return 0 if
the first frame pointer is properly initialized by the startup code.
This function should only be used with a nonzero argument for debugging purposes.
On some targets, the instruction set contains SIMD vector instructions that operate on multiple values contained in one large register at the same time. For example, on the i386 the MMX, 3Dnow! and SSE extensions can be used this way.
The first step in using these extensions is to provide the necessary data
types. This should be done using an appropriate typedef:
typedef int v4si __attribute__ ((mode(V4SI))); |
The base type int is effectively ignored by the compiler, the
actual properties of the new type v4si are defined by the
__attribute__. It defines the machine mode to be used; for vector
types these have the form VnB; n should be the
number of elements in the vector, and B should be the base mode of the
individual elements. The following can be used as base modes:
QI
HI
SI
DI
SF
DF
Specifying a combination that is not valid for the current architecture
will cause gcc to synthesize the instructions using a narrower mode.
For example, if you specify a variable of type V4SI and your
architecture does not allow for this specific SIMD type, gcc will
produce code that uses 4 SIs.
The types defined in this manner can be used with a subset of normal C
operations. Currently, gcc will allow using the following operators on
these types: +, -, *, /, unary minus.
The operations behave like C++ valarrays. Addition is defined as
the addition of the corresponding elements of the operands. For
example, in the code below, each of the 4 elements in a will be
added to the corresponding 4 elements in b and the resulting
vector will be stored in c.
typedef int v4si __attribute__ ((mode(V4SI))); v4si a, b, c; c = a + b; |
Subtraction, multiplication, and division operate in a similar manner. Likewise, the result of using the unary minus operator on a vector type is a vector whose elements are the negative value of the corresponding elements in the operand.
You can declare variables and use them in function calls and returns, as well as in assignments and some casts. You can specify a vector type as a return type for a function. Vector types can also be used as function arguments. It is possible to cast from one vector type to another, provided they are of the same size (in fact, you can also cast vectors to and from other datatypes of the same size).
You cannot operate between vectors of different lengths or different signedness without a cast.
A port that supports hardware vector operations, usually provides a set of built-in functions that can be used to operate on vectors. For example, a function to add two vectors and multiply the result by a third could look like this:
v4si f (v4si a, v4si b, v4si c)
{
v4si tmp = __builtin_addv4si (a, b);
return __builtin_mulv4si (tmp, c);
}
|
GCC provides a large number of built-in functions other than the ones mentioned above. Some of these are for internal use in the processing of exceptions or variable-length argument lists and will not be documented here because they may change from time to time; we do not recommend general use of these functions.
The remaining functions are provided for optimization purposes.
GCC includes built-in versions of many of the functions in the standard
C library. The versions prefixed with __builtin_ will always be
treated as having the same meaning as the C library function even if you
specify the `-fno-builtin' option. (see section 3.4 Options Controlling C Dialect)
Many of these functions are only optimized in certain cases; if they are
not optimized in a particular case, a call to the library function will
be emitted.
The functions abort, exit, _Exit and _exit
are recognized and presumed not to return, but otherwise are not built
in. _exit is not recognized in strict ISO C mode (`-ansi',
`-std=c89' or `-std=c99'). _Exit is not recognized in
strict C89 mode (`-ansi' or `-std=c89'). All these functions
have corresponding versions prefixed with __builtin_, which may be
used even in strict C89 mode.
Outside strict ISO C mode, the functions alloca, bcmp,
bzero, index, rindex, ffs, fputs_unlocked,
printf_unlocked and fprintf_unlocked may be handled as
built-in functions. All these functions have corresponding versions
prefixed with __builtin_, which may be used even in strict C89
mode.
The ISO C99 functions conj, conjf, conjl,
creal, crealf, creall, cimag, cimagf,
cimagl, imaxabs, llabs, snprintf,
vscanf, vsnprintf and vsscanf are handled as built-in
functions except in strict ISO C90 mode. There are also built-in
versions of the ISO C99 functions cosf, cosl,
expf, expl, fabsf, fabsl,
logf, logl, sinf, sinl, sqrtf, and
sqrtl, that are recognized in any mode since ISO C90 reserves
these names for the purpose to which ISO C99 puts them. All these
functions have corresponding versions prefixed with __builtin_.
The ISO C90 functions abs, cos, exp, fabs,
fprintf, fputs, labs, log,
memcmp, memcpy,
memset, printf, putchar, puts, scanf,
sin, snprintf, sprintf, sqrt, sscanf,
strcat,
strchr, strcmp, strcpy, strcspn,
strlen, strncat, strncmp, strncpy,
strpbrk, strrchr, strspn, strstr,
vprintf and vsprintf are all
recognized as built-in functions unless `-fno-builtin' is
specified (or `-fno-builtin-function' is specified for an
individual function). All of these functions have corresponding
versions prefixed with __builtin_.
GCC provides built-in versions of the ISO C99 floating point comparison
macros that avoid raising exceptions for unordered operands. They have
the same names as the standard macros ( isgreater,
isgreaterequal, isless, islessequal,
islessgreater, and isunordered) , with __builtin_
prefixed. We intend for a library implementor to be able to simply
#define each standard macro to its built-in equivalent.
You can use the built-in function __builtin_types_compatible_p to
determine whether two types are the same.
This built-in function returns 1 if the unqualified versions of the types type1 and type2 (which are types, not expressions) are compatible, 0 otherwise. The result of this built-in function can be used in integer constant expressions.
This built-in function ignores top level qualifiers (e.g., const,
volatile). For example, int is equivalent to const
int.
The type int[] and int[5] are compatible. On the other
hand, int and char * are not compatible, even if the size
of their types, on the particular architecture are the same. Also, the
amount of pointer indirection is taken into account when determining
similarity. Consequently, short * is not similar to
short **. Furthermore, two types that are typedefed are
considered compatible if their underlying types are compatible.
An enum type is considered to be compatible with another
enum type. For example, enum {foo, bar} is similar to
enum {hot, dog}.
You would typically use this function in code whose execution varies depending on the arguments' types. For example:
#define foo(x) \
({ \
typeof (x) tmp; \
if (__builtin_types_compatible_p (typeof (x), long double)) \
tmp = foo_long_double (tmp); \
else if (__builtin_types_compatible_p (typeof (x), double)) \
tmp = foo_double (tmp); \
else if (__builtin_types_compatible_p (typeof (x), float)) \
tmp = foo_float (tmp); \
else \
abort (); \
tmp; \
})
|
Note: This construct is only available for C.
You can use the built-in function __builtin_choose_expr to
evaluate code depending on the value of a constant expression. This
built-in function returns exp1 if const_exp, which is a
constant expression that must be able to be determined at compile time,
is nonzero. Otherwise it returns 0.
This built-in function is analogous to the `? :' operator in C, except that the expression returned has its type unaltered by promotion rules. Also, the built-in function does not evaluate the expression that was not chosen. For example, if const_exp evaluates to true, exp2 is not evaluated even if it has side-effects.
This built-in function can return an lvalue if the chosen argument is an lvalue.
If exp1 is returned, the return type is the same as exp1's type. Similarly, if exp2 is returned, its return type is the same as exp2.
Example:
#define foo(x) \
__builtin_choose_expr ( \
__builtin_types_compatible_p (typeof (x), double), \
foo_double (x), \
__builtin_choose_expr ( \
__builtin_types_compatible_p (typeof (x), float), \
foo_float (x), \
/* The void expression results in a compile-time error \
when assigning the result to something. */ \
(void)0))
|
Note: This construct is only available for C. Furthermore, the unused expression (exp1 or exp2 depending on the value of const_exp) may still generate syntax errors. This may change in future revisions.
__builtin_constant_p to
determine if a value is known to be constant at compile-time and hence
that GCC can perform constant-folding on expressions involving that
value. The argument of the function is the value to test. The function
returns the integer 1 if the argument is known to be a compile-time
constant and 0 if it is not known to be a compile-time constant. A
return of 0 does not indicate that the value is not a constant,
but merely that GCC cannot prove it is a constant with the specified
value of the `-O' option.
You would typically use this function in an embedded application where memory was a critical resource. If you have some complex calculation, you may want it to be folded if it involves constants, but need to call a function if it does not. For example:
#define Scale_Value(X) \ (__builtin_constant_p (X) \ ? ((X) * SCALE + OFFSET) : Scale (X)) |
You may use this built-in function in either a macro or an inline function. However, if you use it in an inlined function and pass an argument of the function as the argument to the built-in, GCC will never return 1 when you call the inline function with a string constant or compound literal (see section 5.20 Compound Literals) and will not return 1 when you pass a constant numeric value to the inline function unless you specify the `-O' option.
You may also use __builtin_constant_p in initializers for static
data. For instance, you can write
static const int table[] = {
__builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
/* ... */
};
|
This is an acceptable initializer even if EXPRESSION is not a constant expression. GCC must be more conservative about evaluating the built-in in this case, because it has no opportunity to perform optimization.
Previous versions of GCC did not accept this built-in in data initializers. The earliest version where it is completely safe is 3.0.1.
__builtin_expect to provide the compiler with
branch prediction information. In general, you should prefer to
use actual profile feedback for this (`-fprofile-arcs'), as
programmers are notoriously bad at predicting how their programs
actually perform. However, there are applications in which this
data is hard to collect.
The return value is the value of exp, which should be an integral expression. The value of c must be a compile-time constant. The semantics of the built-in are that it is expected that exp == c. For example:
if (__builtin_expect (x, 0)) foo (); |
would indicate that we do not expect to call foo, since
we expect x to be zero. Since you are limited to integral
expressions for exp, you should use constructions such as
if (__builtin_expect (ptr != NULL, 1)) error (); |
when testing pointer or floating-point values.
__builtin_prefetch into code for which
you know addresses of data in memory that is likely to be accessed soon.
If the target supports them, data prefetch instructions will be generated.
If the prefetch is done early enough before the access then the data will
be in the cache by the time it is accessed.
The value of addr is the address of the memory to prefetch. There are two optional arguments, rw and locality. The value of rw is a compile-time constant one or zero; one means that the prefetch is preparing for a write to the memory address and zero, the default, means that the prefetch is preparing for a read. The value locality must be a compile-time constant integer between zero and three. A value of zero means that the data has no temporal locality, so it need not be left in the cache after the access. A value of three means that the data has a high degree of temporal locality and should be left in all levels of cache possible. Values of one and two mean, respectively, a low or moderate degree of temporal locality. The default is three.
for (i = 0; i < n; i++)
{
a[i] = a[i] + b[i];
__builtin_prefetch (&a[i+j], 1, 1);
__builtin_prefetch (&b[i+j], 0, 1);
/* ... */
}
|
Data prefetch does not generate faults if addr is invalid, but
the address expression itself must be valid. For example, a prefetch
of p->next will not fault if p->next is not a valid
address, but evaluation will fault if p is not a valid address.
If the target does not support data prefetch, the address expression is evaluated if it includes side effects but no other code is generated and GCC does not issue a warning.
DBL_MAX. This function is suitable for implementing the
ISO C macro HUGE_VAL.
__builtin_huge_val, except the return type is float.
__builtin_huge_val, except the return
type is long double.
__builtin_huge_val, except a warning is generated
if the target floating-point format does not support infinities.
This function is suitable for implementing the ISO C99 macro INFINITY.
__builtin_inf, except the return type is float.
__builtin_inf, except the return
type is long double.
nan.
Since ISO C99 defines this function in terms of strtod, which we
do not implement, a description of the parsing is in order. The string
is parsed as by strtol; that is, the base is recognized by
leading `0' or `0x' prefixes. The number parsed is placed
in the significand such that the least significant bit of the number
is at the least significant bit of the significand. The number is
truncated to fit the significand field provided. The significand is
forced to be a quiet NaN.
This function, if given a string literal, is evaluated early enough that it is considered a compile-time constant.
__builtin_nan, except the return type is float.
__builtin_nan, except the return type is long double.
__builtin_nan, except the significand is forced
to be a signaling NaN. The nans function is proposed by
WG14 N965.
__builtin_nans, except the return type is float.
__builtin_nans, except the return type is long double.
On some target machines, GCC supports many built-in functions specific to those machines. Generally these generate calls to specific machine instructions, but allow the compiler to schedule those calls.
5.45.1 Alpha Built-in Functions 5.45.2 X86 Built-in Functions 5.45.3 PowerPC AltiVec Built-in Functions
These built-in functions are available for the Alpha family of processors, depending on the command-line switches used.
The following built-in functions are always available. They all generate the machine instruction that is part of the name.
long __builtin_alpha_implver (void) long __builtin_alpha_rpcc (void) long __builtin_alpha_amask (long) long __builtin_alpha_cmpbge (long, long) long __builtin_alpha_extbl (long, long) long __builtin_alpha_extwl (long, long) long __builtin_alpha_extll (long, long) long __builtin_alpha_extql (long, long) long __builtin_alpha_extwh (long, long) long __builtin_alpha_extlh (long, long) long __builtin_alpha_extqh (long, long) long __builtin_alpha_insbl (long, long) long __builtin_alpha_inswl (long, long) long __builtin_alpha_insll (long, long) long __builtin_alpha_insql (long, long) long __builtin_alpha_inswh (long, long) long __builtin_alpha_inslh (long, long) long __builtin_alpha_insqh (long, long) long __builtin_alpha_mskbl (long, long) long __builtin_alpha_mskwl (long, long) long __builtin_alpha_mskll (long, long) long __builtin_alpha_mskql (long, long) long __builtin_alpha_mskwh (long, long) long __builtin_alpha_msklh (long, long) long __builtin_alpha_mskqh (long, long) long __builtin_alpha_umulh (long, long) long __builtin_alpha_zap (long, long) long __builtin_alpha_zapnot (long, long) |
The following built-in functions are always with `-mmax'
or `-mcpu=cpu' where cpu is pca56 or
later. They all generate the machine instruction that is part
of the name.
long __builtin_alpha_pklb (long) long __builtin_alpha_pkwb (long) long __builtin_alpha_unpkbl (long) long __builtin_alpha_unpkbw (long) long __builtin_alpha_minub8 (long, long) long __builtin_alpha_minsb8 (long, long) long __builtin_alpha_minuw4 (long, long) long __builtin_alpha_minsw4 (long, long) long __builtin_alpha_maxub8 (long, long) long __builtin_alpha_maxsb8 (long, long) long __builtin_alpha_maxuw4 (long, long) long __builtin_alpha_maxsw4 (long, long) long __builtin_alpha_perr (long, long) |
The following built-in functions are always with `-mcix'
or `-mcpu=cpu' where cpu is ev67 or
later. They all generate the machine instruction that is part
of the name.
long __builtin_alpha_cttz (long) long __builtin_alpha_ctlz (long) long __builtin_alpha_ctpop (long) |
The following builtins are available on systems that use the OSF/1
PALcode. Normally they invoke the rduniq and wruniq
PAL calls, but when invoked with `-mtls-kernel', they invoke
rdval and wrval.
void *__builtin_thread_pointer (void) void __builtin_set_thread_pointer (void *) |
These built-in functions are available for the i386 and x86-64 family of computers, depending on the command-line switches used.
The following machine modes are available for use with MMX built-in functions
(see section 5.43 Using vector instructions through built-in functions): V2SI for a vector of two 32-bit integers,
V4HI for a vector of four 16-bit integers, and V8QI for a
vector of eight 8-bit integers. Some of the built-in functions operate on
MMX registers as a whole 64-bit entity, these use DI as their mode.
If 3Dnow extensions are enabled, V2SF is used as a mode for a vector
of two 32-bit floating point values.
If SSE extensions are enabled, V4SF is used for a vector of four 32-bit
floating point values. Some instructions use a vector of four 32-bit
integers, these use V4SI. Finally, some instructions operate on an
entire vector register, interpreting it as a 128-bit integer, these use mode
TI.
The following built-in functions are made available by `-mmmx'. All of them generate the machine instruction that is part of the name.
v8qi __builtin_ia32_paddb (v8qi, v8qi) v4hi __builtin_ia32_paddw (v4hi, v4hi) v2si __builtin_ia32_paddd (v2si, v2si) v8qi __builtin_ia32_psubb (v8qi, v8qi) v4hi __builtin_ia32_psubw (v4hi, v4hi) v2si __builtin_ia32_psubd (v2si, v2si) v8qi __builtin_ia32_paddsb (v8qi, v8qi) v4hi __builtin_ia32_paddsw (v4hi, v4hi) v8qi __builtin_ia32_psubsb (v8qi, v8qi) v4hi __builtin_ia32_psubsw (v4hi, v4hi) v8qi __builtin_ia32_paddusb (v8qi, v8qi) v4hi __builtin_ia32_paddusw (v4hi, v4hi) v8qi __builtin_ia32_psubusb (v8qi, v8qi) v4hi __builtin_ia32_psubusw (v4hi, v4hi) v4hi __builtin_ia32_pmullw (v4hi, v4hi) v4hi __builtin_ia32_pmulhw (v4hi, v4hi) di __builtin_ia32_pand (di, di) di __builtin_ia32_pandn (di,di) di __builtin_ia32_por (di, di) di __builtin_ia32_pxor (di, di) v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi) v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi) v2si __builtin_ia32_pcmpeqd (v2si, v2si) v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi) v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi) v2si __builtin_ia32_pcmpgtd (v2si, v2si) v8qi __builtin_ia32_punpckhbw (v8qi, v8qi) v4hi __builtin_ia32_punpckhwd (v4hi, v4hi) v2si __builtin_ia32_punpckhdq (v2si, v2si) v8qi __builtin_ia32_punpcklbw (v8qi, v8qi) v4hi __builtin_ia32_punpcklwd (v4hi, v4hi) v2si __builtin_ia32_punpckldq (v2si, v2si) v8qi __builtin_ia32_packsswb (v4hi, v4hi) v4hi __builtin_ia32_packssdw (v2si, v2si) v8qi __builtin_ia32_packuswb (v4hi, v4hi) |
The following built-in functions are made available either with `-msse', or with a combination of `-m3dnow' and `-march=athlon'. All of them generate the machine instruction that is part of the name.
v4hi __builtin_ia32_pmulhuw (v4hi, v4hi) v8qi __builtin_ia32_pavgb (v8qi, v8qi) v4hi __builtin_ia32_pavgw (v4hi, v4hi) v4hi __builtin_ia32_psadbw (v8qi, v8qi) v8qi __builtin_ia32_pmaxub (v8qi, v8qi) v4hi __builtin_ia32_pmaxsw (v4hi, v4hi) v8qi __builtin_ia32_pminub (v8qi, v8qi) v4hi __builtin_ia32_pminsw (v4hi, v4hi) int __builtin_ia32_pextrw (v4hi, int) v4hi __builtin_ia32_pinsrw (v4hi, int, int) int __builtin_ia32_pmovmskb (v8qi) void __builtin_ia32_maskmovq (v8qi, v8qi, char *) void __builtin_ia32_movntq (di *, di) void __builtin_ia32_sfence (void) |
The following built-in functions are available when `-msse' is used. All of them generate the machine instruction that is part of the name.
int __builtin_ia32_comieq (v4sf, v4sf) int __builtin_ia32_comineq (v4sf, v4sf) int __builtin_ia32_comilt (v4sf, v4sf) int __builtin_ia32_comile (v4sf, v4sf) int __builtin_ia32_comigt (v4sf, v4sf) int __builtin_ia32_comige (v4sf, v4sf) int __builtin_ia32_ucomieq (v4sf, v4sf) int __builtin_ia32_ucomineq (v4sf, v4sf) int __builtin_ia32_ucomilt (v4sf, v4sf) int __builtin_ia32_ucomile (v4sf, v4sf) int __builtin_ia32_ucomigt (v4sf, v4sf) int __builtin_ia32_ucomige (v4sf, v4sf) v4sf __builtin_ia32_addps (v4sf, v4sf) v4sf __builtin_ia32_subps (v4sf, v4sf) v4sf __builtin_ia32_mulps (v4sf, v4sf) v4sf __builtin_ia32_divps (v4sf, v4sf) v4sf __builtin_ia32_addss (v4sf, v4sf) v4sf __builtin_ia32_subss (v4sf, v4sf) v4sf __builtin_ia32_mulss (v4sf, v4sf) v4sf __builtin_ia32_divss (v4sf, v4sf) v4si __builtin_ia32_cmpeqps (v4sf, v4sf) v4si __builtin_ia32_cmpltps (v4sf, v4sf) v4si __builtin_ia32_cmpleps (v4sf, v4sf) v4si __builtin_ia32_cmpgtps (v4sf, v4sf) v4si __builtin_ia32_cmpgeps (v4sf, v4sf) v4si __builtin_ia32_cmpunordps (v4sf, v4sf) v4si __builtin_ia32_cmpneqps (v4sf, v4sf) v4si __builtin_ia32_cmpnltps (v4sf, v4sf) v4si __builtin_ia32_cmpnleps (v4sf, v4sf) v4si __builtin_ia32_cmpngtps (v4sf, v4sf) v4si __builtin_ia32_cmpngeps (v4sf, v4sf) v4si __builtin_ia32_cmpordps (v4sf, v4sf) v4si __builtin_ia32_cmpeqss (v4sf, v4sf) v4si __builtin_ia32_cmpltss (v4sf, v4sf) v4si __builtin_ia32_cmpless (v4sf, v4sf) v4si __builtin_ia32_cmpunordss (v4sf, v4sf) v4si __builtin_ia32_cmpneqss (v4sf, v4sf) v4si __builtin_ia32_cmpnlts (v4sf, v4sf) v4si __builtin_ia32_cmpnless (v4sf, v4sf) v4si __builtin_ia32_cmpordss (v4sf, v4sf) v4sf __builtin_ia32_maxps (v4sf, v4sf) v4sf __builtin_ia32_maxss (v4sf, v4sf) v4sf __builtin_ia32_minps (v4sf, v4sf) v4sf __builtin_ia32_minss (v4sf, v4sf) v4sf __builtin_ia32_andps (v4sf, v4sf) v4sf __builtin_ia32_andnps (v4sf, v4sf) v4sf __builtin_ia32_orps (v4sf, v4sf) v4sf __builtin_ia32_xorps (v4sf, v4sf) v4sf __builtin_ia32_movss (v4sf, v4sf) v4sf __builtin_ia32_movhlps (v4sf, v4sf) v4sf __builtin_ia32_movlhps (v4sf, v4sf) v4sf __builtin_ia32_unpckhps (v4sf, v4sf) v4sf __builtin_ia32_unpcklps (v4sf, v4sf) v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si) v4sf __builtin_ia32_cvtsi2ss (v4sf, int) v2si __builtin_ia32_cvtps2pi (v4sf) int __builtin_ia32_cvtss2si (v4sf) v2si __builtin_ia32_cvttps2pi (v4sf) int __builtin_ia32_cvttss2si (v4sf) v4sf __builtin_ia32_rcpps (v4sf) v4sf __builtin_ia32_rsqrtps (v4sf) v4sf __builtin_ia32_sqrtps (v4sf) v4sf __builtin_ia32_rcpss (v4sf) v4sf __builtin_ia32_rsqrtss (v4sf) v4sf __builtin_ia32_sqrtss (v4sf) v4sf __builtin_ia32_shufps (v4sf, v4sf, int) void __builtin_ia32_movntps (float *, v4sf) int __builtin_ia32_movmskps (v4sf) |
The following built-in functions are available when `-msse' is used.
v4sf __builtin_ia32_loadaps (float *)
movaps machine instruction as a load from memory.
void __builtin_ia32_storeaps (float *, v4sf)
movaps machine instruction as a store to memory.
v4sf __builtin_ia32_loadups (float *)
movups machine instruction as a load from memory.
void __builtin_ia32_storeups (float *, v4sf)
movups machine instruction as a store to memory.
v4sf __builtin_ia32_loadsss (float *)
movss machine instruction as a load from memory.
void __builtin_ia32_storess (float *, v4sf)
movss machine instruction as a store to memory.
v4sf __builtin_ia32_loadhps (v4sf, v2si *)
movhps machine instruction as a load from memory.
v4sf __builtin_ia32_loadlps (v4sf, v2si *)
movlps machine instruction as a load from memory
void __builtin_ia32_storehps (v4sf, v2si *)
movhps machine instruction as a store to memory.
void __builtin_ia32_storelps (v4sf, v2si *)
movlps machine instruction as a store to memory.
The following built-in functions are available when `-msse3' is used. All of them generate the machine instruction that is part of the name.
v2df __builtin_ia32_addsubpd (v2df, v2df) v2df __builtin_ia32_addsubps (v2df, v2df) v2df __builtin_ia32_haddpd (v2df, v2df) v2df __builtin_ia32_haddps (v2df, v2df) v2df __builtin_ia32_hsubpd (v2df, v2df) v2df __builtin_ia32_hsubps (v2df, v2df) v16qi __builtin_ia32_lddqu (char const *) void __builtin_ia32_monitor (void *, unsigned int, unsigned int) v2df __builtin_ia32_movddup (v2df) v4sf __builtin_ia32_movshdup (v4sf) v4sf __builtin_ia32_movsldup (v4sf) void __builtin_ia32_mwait (unsigned int, unsigned int) |
The following built-in functions are available when `-msse3' is used.
v2df __builtin_ia32_loadddup (double const *)
movddup machine instruction as a load from memory.
The following built-in functions are available when `-m3dnow' is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_femms (void) v8qi __builtin_ia32_pavgusb (v8qi, v8qi) v2si __builtin_ia32_pf2id (v2sf) v2sf __builtin_ia32_pfacc (v2sf, v2sf) v2sf __builtin_ia32_pfadd (v2sf, v2sf) v2si __builtin_ia32_pfcmpeq (v2sf, v2sf) v2si __builtin_ia32_pfcmpge (v2sf, v2sf) v2si __builtin_ia32_pfcmpgt (v2sf, v2sf) v2sf __builtin_ia32_pfmax (v2sf, v2sf) v2sf __builtin_ia32_pfmin (v2sf, v2sf) v2sf __builtin_ia32_pfmul (v2sf, v2sf) v2sf __builtin_ia32_pfrcp (v2sf) v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf) v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf) v2sf __builtin_ia32_pfrsqrt (v2sf) v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf) v2sf __builtin_ia32_pfsub (v2sf, v2sf) v2sf __builtin_ia32_pfsubr (v2sf, v2sf) v2sf __builtin_ia32_pi2fd (v2si) v4hi __builtin_ia32_pmulhrw (v4hi, v4hi) |
The following built-in functions are available when both `-m3dnow' and `-march=athlon' are used. All of them generate the machine instruction that is part of the name.
v2si __builtin_ia32_pf2iw (v2sf) v2sf __builtin_ia32_pfnacc (v2sf, v2sf) v2sf __builtin_ia32_pfpnacc (v2sf, v2sf) v2sf __builtin_ia32_pi2fw (v2si) v2sf __builtin_ia32_pswapdsf (v2sf) v2si __builtin_ia32_pswapdsi (v2si) |
These built-in functions are available for the PowerPC family of computers, depending on the command-line switches used.
The following machine modes are available for use with AltiVec built-in
functions (see section 5.43 Using vector instructions through built-in functions): V4SI for a vector of four
32-bit integers, V4SF for a vector of four 32-bit floating point
numbers, V8HI for a vector of eight 16-bit integers, and
V16QI for a vector of sixteen 8-bit integers.
The following functions are made available by including
<altivec.h> and using `-maltivec' and
`-mabi=altivec'. The functions implement the functionality
described in Motorola's AltiVec Programming Interface Manual.
There are a few differences from Motorola's documentation and GCC's
implementation. Vector constants are done with curly braces (not
parentheses). Vector initializers require no casts if the vector
constant is of the same type as the variable it is initializing. The
vector bool type is deprecated and will be discontinued in
further revisions. Use vector signed instead. If signed
or unsigned is omitted, the vector type will default to
signed. Lastly, all overloaded functions are implemented with macros
for the C implementation. So code the following example will not work:
vec_add ((vector signed int){1, 2, 3, 4}, foo);
|
Since vec_add is a macro, the vector constant in the above example will be treated as four different arguments. Wrap the entire argument in parentheses for this to work. The C++ implementation does not use macros.
Note: Only the <altivec.h> interface is supported.
Internally, GCC uses built-in functions to achieve the functionality in
the aforementioned header file, but they are not supported and are
subject to change without notice.
vector signed char vec_abs (vector signed char, vector signed char);
vector signed short vec_abs (vector signed short, vector signed short);
vector signed int vec_abs (vector signed int, vector signed int);
vector signed float vec_abs (vector signed float, vector signed float);
vector signed char vec_abss (vector signed char, vector signed char);
vector signed short vec_abss (vector signed short, vector signed short);
vector signed char vec_add (vector signed char, vector signed char);
vector unsigned char vec_add (vector signed char, vector unsigned char);
vector unsigned char vec_add (vector unsigned char, vector signed char);
vector unsigned char vec_add (vector unsigned char,
vector unsigned char);
vector signed short vec_add (vector signed short, vector signed short);
vector unsigned short vec_add (vector signed short,
vector unsigned short);
vector unsigned short vec_add (vector unsigned short,
vector signed short);
vector unsigned short vec_add (vector unsigned short,
vector unsigned short);
vector signed int vec_add (vector signed int, vector signed int);
vector unsigned int vec_add (vector signed int, vector unsigned int);
vector unsigned int vec_add (vector unsigned int, vector signed int);
vector unsigned int vec_add (vector unsigned int, vector unsigned int);
vector float vec_add (vector float, vector float);
vector unsigned int vec_addc (vector unsigned int, vector unsigned int);
vector unsigned char vec_adds (vector signed char,
vector unsigned char);
vector unsigned char vec_adds (vector unsigned char,
vector signed char);
vector unsigned char vec_adds (vector unsigned char,
vector unsigned char);
vector signed char vec_adds (vector signed char, vector signed char);
vector unsigned short vec_adds (vector signed short,
vector unsigned short);
vector unsigned short vec_adds (vector unsigned short,
vector signed short);
vector unsigned short vec_adds (vector unsigned short,
vector unsigned short);
vector signed short vec_adds (vector signed short, vector signed short);
vector unsigned int vec_adds (vector signed int, vector unsigned int);
vector unsigned int vec_adds (vector unsigned int, vector signed int);
vector unsigned int vec_adds (vector unsigned int, vector unsigned int);
vector signed int vec_adds (vector signed int, vector signed int);
vector float vec_and (vector float, vector float);
vector float vec_and (vector float, vector signed int);
vector float vec_and (vector signed int, vector float);
vector signed int vec_and (vector signed int, vector signed int);
vector unsigned int vec_and (vector signed int, vector unsigned int);
vector unsigned int vec_and (vector unsigned int, vector signed int);
vector unsigned int vec_and (vector unsigned int, vector unsigned int);
vector signed short vec_and (vector signed short, vector signed short);
vector unsigned short vec_and (vector signed short,
vector unsigned short);
vector unsigned short vec_and (vector unsigned short,
vector signed short);
vector unsigned short vec_and (vector unsigned short,
vector unsigned short);
vector signed char vec_and (vector signed char, vector signed char);
vector unsigned char vec_and (vector signed char, vector unsigned char);
vector unsigned char vec_and (vector unsigned char, vector signed char);
vector unsigned char vec_and (vector unsigned char,
vector unsigned char);
vector float vec_andc (vector float, vector float);
vector float vec_andc (vector float, vector signed int);
vector float vec_andc (vector signed int, vector float);
vector signed int vec_andc (vector signed int, vector signed int);
vector unsigned int vec_andc (vector signed int, vector unsigned int);
vector unsigned int vec_andc (vector unsigned int, vector signed int);
vector unsigned int vec_andc (vector unsigned int, vector unsigned int);
vector signed short vec_andc (vector signed short, vector signed short);
vector unsigned short vec_andc (vector signed short,
vector unsigned short);
vector unsigned short vec_andc (vector unsigned short,
vector signed short);
vector unsigned short vec_andc (vector unsigned short,
vector unsigned short);
vector signed char vec_andc (vector signed char, vector signed char);
vector unsigned char vec_andc (vector signed char,
vector unsigned char);
vector unsigned char vec_andc (vector unsigned char,
vector signed char);
vector unsigned char vec_andc (vector unsigned char,
vector unsigned char);
vector unsigned char vec_avg (vector unsigned char,
vector unsigned char);
vector signed char vec_avg (vector signed char, vector signed char);
vector unsigned short vec_avg (vector unsigned short,
vector unsigned short);
vector signed short vec_avg (vector signed short, vector signed short);
vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
vector signed int vec_avg (vector signed int, vector signed int);
vector float vec_ceil (vector float);
vector signed int vec_cmpb (vector float, vector float);
vector signed char vec_cmpeq (vector signed char, vector signed char);
vector signed char vec_cmpeq (vector unsigned char,
vector unsigned char);
vector signed short vec_cmpeq (vector signed short,
vector signed short);
vector signed short vec_cmpeq (vector unsigned short,
vector unsigned short);
vector signed int vec_cmpeq (vector signed int, vector signed int);
vector signed int vec_cmpeq (vector unsigned int, vector unsigned int);
vector signed int vec_cmpeq (vector float, vector float);
vector signed int vec_cmpge (vector float, vector float);
vector signed char vec_cmpgt (vector unsigned char,
vector unsigned char);
vector signed char vec_cmpgt (vector signed char, vector signed char);
vector signed short vec_cmpgt (vector unsigned short,
vector unsigned short);
vector signed short vec_cmpgt (vector signed short,
vector signed short);
vector signed int vec_cmpgt (vector unsigned int, vector unsigned int);
vector signed int vec_cmpgt (vector signed int, vector signed int);
vector signed int vec_cmpgt (vector float, vector float);
vector signed int vec_cmple (vector float, vector float);
vector signed char vec_cmplt (vector unsigned char,
vector unsigned char);
vector signed char vec_cmplt (vector signed char, vector signed char);
vector signed short vec_cmplt (vector unsigned short,
vector unsigned short);
vector signed short vec_cmplt (vector signed short,
vector signed short);
vector signed int vec_cmplt (vector unsigned int, vector unsigned int);
vector signed int vec_cmplt (vector signed int, vector signed int);
vector signed int vec_cmplt (vector float, vector float);
vector float vec_ctf (vector unsigned int, const char);
vector float vec_ctf (vector signed int, const char);
vector signed int vec_cts (vector float, const char);
vector unsigned int vec_ctu (vector float, const char);
void vec_dss (const char);
void vec_dssall (void);
void vec_dst (void *, int, const char);
void vec_dstst (void *, int, const char);
void vec_dststt (void *, int, const char);
void vec_dstt (void *, int, const char);
vector float vec_expte (vector float, vector float);
vector float vec_floor (vector float, vector float);
vector float vec_ld (int, vector float *);
vector float vec_ld (int, float *):
vector signed int vec_ld (int, int *);
vector signed int vec_ld (int, vector signed int *);
vector unsigned int vec_ld (int, vector unsigned int *);
vector unsigned int vec_ld (int, unsigned int *);
vector signed short vec_ld (int, short *, vector signed short *);
vector unsigned short vec_ld (int, unsigned short *,
vector unsigned short *);
vector signed char vec_ld (int, signed char *);
vector signed char vec_ld (int, vector signed char *);
vector unsigned char vec_ld (int, unsigned char *);
vector unsigned char vec_ld (int, vector unsigned char *);
vector signed char vec_lde (int, signed char *);
vector unsigned char vec_lde (int, unsigned char *);
vector signed short vec_lde (int, short *);
vector unsigned short vec_lde (int, unsigned short *);
vector float vec_lde (int, float *);
vector signed int vec_lde (int, int *);
vector unsigned int vec_lde (int, unsigned int *);
void float vec_ldl (int, float *);
void float vec_ldl (int, vector float *);
void signed int vec_ldl (int, vector signed int *);
void signed int vec_ldl (int, int *);
void unsigned int vec_ldl (int, unsigned int *);
void unsigned int vec_ldl (int, vector unsigned int *);
void signed short vec_ldl (int, vector signed short *);
void signed short vec_ldl (int, short *);
void unsigned short vec_ldl (int, vector unsigned short *);
void unsigned short vec_ldl (int, unsigned short *);
void signed char vec_ldl (int, vector signed char *);
void signed char vec_ldl (int, signed char *);
void unsigned char vec_ldl (int, vector unsigned char *);
void unsigned char vec_ldl (int, unsigned char *);
vector float vec_loge (vector float);
vector unsigned char vec_lvsl (int, void *, int *);
vector unsigned char vec_lvsr (int, void *, int *);
vector float vec_madd (vector float, vector float, vector float);
vector signed short vec_madds (vector signed short, vector signed short,
vector signed short);
vector unsigned char vec_max (vector signed char, vector unsigned char);
vector unsigned char vec_max (vector unsigned char, vector signed char);
vector unsigned char vec_max (vector unsigned char,
vector unsigned char);
vector signed char vec_max (vector signed char, vector signed char);
vector unsigned short vec_max (vector signed short,
vector unsigned short);
vector unsigned short vec_max (vector unsigned short,
vector signed short);
vector unsigned short vec_max (vector unsigned short,
vector unsigned short);
vector signed short vec_max (vector signed short, vector signed short);
vector unsigned int vec_max (vector signed int, vector unsigned int);
vector unsigned int vec_max (vector unsigned int, vector signed int);
vector unsigned int vec_max (vector unsigned int, vector unsigned int);
vector signed int vec_max (vector signed int, vector signed int);
vector float vec_max (vector float, vector float);
vector signed char vec_mergeh (vector signed char, vector signed char);
vector unsigned char vec_mergeh (vector unsigned char,
vector unsigned char);
vector signed short vec_mergeh (vector signed short,
vector signed short);
vector unsigned short vec_mergeh (vector unsigned short,
vector unsigned short);
vector float vec_mergeh (vector float, vector float);
vector signed int vec_mergeh (vector signed int, vector signed int);
vector unsigned int vec_mergeh (vector unsigned int,
vector unsigned int);
vector signed char vec_mergel (vector signed char, vector signed char);
vector unsigned char vec_mergel (vector unsigned char,
vector unsigned char);
vector signed short vec_mergel (vector signed short,
vector signed short);
vector unsigned short vec_mergel (vector unsigned short,
vector unsigned short);
vector float vec_mergel (vector float, vector float);
vector signed int vec_mergel (vector signed int, vector signed int);
vector unsigned int vec_mergel (vector unsigned int,
vector unsigned int);
vector unsigned short vec_mfvscr (void);
vector unsigned char vec_min (vector signed char, vector unsigned char);
vector unsigned char vec_min (vector unsigned char, vector signed char);
vector unsigned char vec_min (vector unsigned char,
vector unsigned char);
vector signed char vec_min (vector signed char, vector signed char);
vector unsigned short vec_min (vector signed short,
vector unsigned short);
vector unsigned short vec_min (vector unsigned short,
vector signed short);
vector unsigned short vec_min (vector unsigned short,
vector unsigned short);
vector signed short vec_min (vector signed short, vector signed short);
vector unsigned int vec_min (vector signed int, vector unsigned int);
vector unsigned int vec_min (vector unsigned int, vector signed int);
vector unsigned int vec_min (vector unsigned int, vector unsigned int);
vector signed int vec_min (vector signed int, vector signed int);
vector float vec_min (vector float, vector float);
vector signed short vec_mladd (vector signed short, vector signed short,
vector signed short);
vector signed short vec_mladd (vector signed short,
vector unsigned short,
vector unsigned short);
vector signed short vec_mladd (vector unsigned short,
vector signed short,
vector signed short);
vector unsigned short vec_mladd (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector signed short vec_mradds (vector signed short,
vector signed short,
vector signed short);
vector unsigned int vec_msum (vector unsigned char,
vector unsigned char,
vector unsigned int);
vector signed int vec_msum (vector signed char, vector unsigned char,
vector signed int);
vector unsigned int vec_msum (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_msum (vector signed short, vector signed short,
vector signed int);
vector unsigned int vec_msums (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_msums (vector signed short, vector signed short,
vector signed int);
void vec_mtvscr (vector signed int);
void vec_mtvscr (vector unsigned int);
void vec_mtvscr (vector signed short);
void vec_mtvscr (vector unsigned short);
void vec_mtvscr (vector signed char);
void vec_mtvscr (vector unsigned char);
vector unsigned short vec_mule (vector unsigned char,
vector unsigned char);
vector signed short vec_mule (vector signed char, vector signed char);
vector unsigned int vec_mule (vector unsigned short,
vector unsigned short);
vector signed int vec_mule (vector signed short, vector signed short);
vector unsigned short vec_mulo (vector unsigned char,
vector unsigned char);
vector signed short vec_mulo (vector signed char, vector signed char);
vector unsigned int vec_mulo (vector unsigned short,
vector unsigned short);
vector signed int vec_mulo (vector signed short, vector signed short);
vector float vec_nmsub (vector float, vector float, vector float);
vector float vec_nor (vector float, vector float);
vector signed int vec_nor (vector signed int, vector signed int);
vector unsigned int vec_nor (vector unsigned int, vector unsigned int);
vector signed short vec_nor (vector signed short, vector signed short);
vector unsigned short vec_nor (vector unsigned short,
vector unsigned short);
vector signed char vec_nor (vector signed char, vector signed char);
vector unsigned char vec_nor (vector unsigned char,
vector unsigned char);
vector float vec_or (vector float, vector float);
vector float vec_or (vector float, vector signed int);
vector float vec_or (vector signed int, vector float);
vector signed int vec_or (vector signed int, vector signed int);
vector unsigned int vec_or (vector signed int, vector unsigned int);
vector unsigned int vec_or (vector unsigned int, vector signed int);
vector unsigned int vec_or (vector unsigned int, vector unsigned int);
vector signed short vec_or (vector signed short, vector signed short);
vector unsigned short vec_or (vector signed short,
vector unsigned short);
vector unsigned short vec_or (vector unsigned short,
vector signed short);
vector unsigned short vec_or (vector unsigned short,
vector unsigned short);
vector signed char vec_or (vector signed char, vector signed char);
vector unsigned char vec_or (vector signed char, vector unsigned char);
vector unsigned char vec_or (vector unsigned char, vector signed char);
vector unsigned char vec_or (vector unsigned char,
vector unsigned char);
vector signed char vec_pack (vector signed short, vector signed short);
vector unsigned char vec_pack (vector unsigned short,
vector unsigned short);
vector signed short vec_pack (vector signed int, vector signed int);
vector unsigned short vec_pack (vector unsigned int,
vector unsigned int);
vector signed short vec_packpx (vector unsigned int,
vector unsigned int);
vector unsigned char vec_packs (vector unsigned short,
vector unsigned short);
vector signed char vec_packs (vector signed short, vector signed short);
vector unsigned short vec_packs (vector unsigned int,
vector unsigned int);
vector signed short vec_packs (vector signed int, vector signed int);
vector unsigned char vec_packsu (vector unsigned short,
vector unsigned short);
vector unsigned char vec_packsu (vector signed short,
vector signed short);
vector unsigned short vec_packsu (vector unsigned int,
vector unsigned int);
vector unsigned short vec_packsu (vector signed int, vector signed int);
vector float vec_perm (vector float, vector float,
vector unsigned char);
vector signed int vec_perm (vector signed int, vector signed int,
vector unsigned char);
vector unsigned int vec_perm (vector unsigned int, vector unsigned int,
vector unsigned char);
vector signed short vec_perm (vector signed short, vector signed short,
vector unsigned char);
vector unsigned short vec_perm (vector unsigned short,
vector unsigned short,
vector unsigned char);
vector signed char vec_perm (vector signed char, vector signed char,
vector unsigned char);
vector unsigned char vec_perm (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector float vec_re (vector float);
vector signed char vec_rl (vector signed char, vector unsigned char);
vector unsigned char vec_rl (vector unsigned char,
vector unsigned char);
vector signed short vec_rl (vector signed short, vector unsigned short);
vector unsigned short vec_rl (vector unsigned short,
vector unsigned short);
vector signed int vec_rl (vector signed int, vector unsigned int);
vector unsigned int vec_rl (vector unsigned int, vector unsigned int);
vector float vec_round (vector float);
vector float vec_rsqrte (vector float);
vector float vec_sel (vector float, vector float, vector signed int);
vector float vec_sel (vector float, vector float, vector unsigned int);
vector signed int vec_sel (vector signed int, vector signed int,
vector signed int);
vector signed int vec_sel (vector signed int, vector signed int,
vector unsigned int);
vector unsigned int vec_sel (vector unsigned int, vector unsigned int,
vector signed int);
vector unsigned int vec_sel (vector unsigned int, vector unsigned int,
vector unsigned int);
vector signed short vec_sel (vector signed short, vector signed short,
vector signed short);
vector signed short vec_sel (vector signed short, vector signed short,
vector unsigned short);
vector unsigned short vec_sel (vector unsigned short,
vector unsigned short,
vector signed short);
vector unsigned short vec_sel (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector signed char vec_sel (vector signed char, vector signed char,
vector signed char);
vector signed char vec_sel (vector signed char, vector signed char,
vector unsigned char);
vector unsigned char vec_sel (vector unsigned char,
vector unsigned char,
vector signed char);
vector unsigned char vec_sel (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector signed char vec_sl (vector signed char, vector unsigned char);
vector unsigned char vec_sl (vector unsigned char,
vector unsigned char);
vector signed short vec_sl (vector signed short, vector unsigned short);
vector unsigned short vec_sl (vector unsigned short,
vector unsigned short);
vector signed int vec_sl (vector signed int, vector unsigned int);
vector unsigned int vec_sl (vector unsigned int, vector unsigned int);
vector float vec_sld (vector float, vector float, const char);
vector signed int vec_sld (vector signed int, vector signed int,
const char);
vector unsigned int vec_sld (vector unsigned int, vector unsigned int,
const char);
vector signed short vec_sld (vector signed short, vector signed short,
const char);
vector unsigned short vec_sld (vector unsigned short,
vector unsigned short, const char);
vector signed char vec_sld (vector signed char, vector signed char,
const char);
vector unsigned char vec_sld (vector unsigned char,
vector unsigned char,
const char);
vector signed int vec_sll (vector signed int, vector unsigned int);
vector signed int vec_sll (vector signed int, vector unsigned short);
vector signed int vec_sll (vector signed int, vector unsigned char);
vector unsigned int vec_sll (vector unsigned int, vector unsigned int);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned short);
vector unsigned int vec_sll (vector unsigned int, vector unsigned char);
vector signed short vec_sll (vector signed short, vector unsigned int);
vector signed short vec_sll (vector signed short,
vector unsigned short);
vector signed short vec_sll (vector signed short, vector unsigned char);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned int);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned short);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned char);
vector signed char vec_sll (vector signed char, vector unsigned int);
vector signed char vec_sll (vector signed char, vector unsigned short);
vector signed char vec_sll (vector signed char, vector unsigned char);
vector unsigned char vec_sll (vector unsigned char,
vector unsigned int);
vector unsigned char vec_sll (vector unsigned char,
vector unsigned short);
vector unsigned char vec_sll (vector unsigned char,
vector unsigned char);
vector float vec_slo (vector float, vector signed char);
vector float vec_slo (vector float, vector unsigned char);
vector signed int vec_slo (vector signed int, vector signed char);
vector signed int vec_slo (vector signed int, vector unsigned char);
vector unsigned int vec_slo (vector unsigned int, vector signed char);
vector unsigned int vec_slo (vector unsigned int, vector unsigned char);
vector signed short vec_slo (vector signed short, vector signed char);
vector signed short vec_slo (vector signed short, vector unsigned char);
vector unsigned short vec_slo (vector unsigned short,
vector signed char);
vector unsigned short vec_slo (vector unsigned short,
vector unsigned char);
vector signed char vec_slo (vector signed char, vector signed char);
vector signed char vec_slo (vector signed char, vector unsigned char);
vector unsigned char vec_slo (vector unsigned char, vector signed char);
vector unsigned char vec_slo (vector unsigned char,
vector unsigned char);
vector signed char vec_splat (vector signed char, const char);
vector unsigned char vec_splat (vector unsigned char, const char);
vector signed short vec_splat (vector signed short, const char);
vector unsigned short vec_splat (vector unsigned short, const char);
vector float vec_splat (vector float, const char);
vector signed int vec_splat (vector signed int, const char);
vector unsigned int vec_splat (vector unsigned int, const char);
vector signed char vec_splat_s8 (const char);
vector signed short vec_splat_s16 (const char);
vector signed int vec_splat_s32 (const char);
vector unsigned char vec_splat_u8 (const char);
vector unsigned short vec_splat_u16 (const char);
vector unsigned int vec_splat_u32 (const char);
vector signed char vec_sr (vector signed char, vector unsigned char);
vector unsigned char vec_sr (vector unsigned char,
vector unsigned char);
vector signed short vec_sr (vector signed short, vector unsigned short);
vector unsigned short vec_sr (vector unsigned short,
vector unsigned short);
vector signed int vec_sr (vector signed int, vector unsigned int);
vector unsigned int vec_sr (vector unsigned int, vector unsigned int);
vector signed char vec_sra (vector signed char, vector unsigned char);
vector unsigned char vec_sra (vector unsigned char,
vector unsigned char);
vector signed short vec_sra (vector signed short,
vector unsigned short);
vector unsigned short vec_sra (vector unsigned short,
vector unsigned short);
vector signed int vec_sra (vector signed int, vector unsigned int);
vector unsigned int vec_sra (vector unsigned int, vector unsigned int);
vector signed int vec_srl (vector signed int, vector unsigned int);
vector signed int vec_srl (vector signed int, vector unsigned short);
vector signed int vec_srl (vector signed int, vector unsigned char);
vector unsigned int vec_srl (vector unsigned int, vector unsigned int);
vector unsigned int vec_srl (vector unsigned int,
vector unsigned short);
vector unsigned int vec_srl (vector unsigned int, vector unsigned char);
vector signed short vec_srl (vector signed short, vector unsigned int);
vector signed short vec_srl (vector signed short,
vector unsigned short);
vector signed short vec_srl (vector signed short, vector unsigned char);
vector unsigned short vec_srl (vector unsigned short,
vector unsigned int);
vector unsigned short vec_srl (vector unsigned short,
vector unsigned short);
vector unsigned short vec_srl (vector unsigned short,
vector unsigned char);
vector signed char vec_srl (vector signed char, vector unsigned int);
vector signed char vec_srl (vector signed char, vector unsigned short);
vector signed char vec_srl (vector signed char, vector unsigned char);
vector unsigned char vec_srl (vector unsigned char,
vector unsigned int);
vector unsigned char vec_srl (vector unsigned char,
vector unsigned short);
vector unsigned char vec_srl (vector unsigned char,
vector unsigned char);
vector float vec_sro (vector float, vector signed char);
vector float vec_sro (vector float, vector unsigned char);
vector signed int vec_sro (vector signed int, vector signed char);
vector signed int vec_sro (vector signed int, vector unsigned char);
vector unsigned int vec_sro (vector unsigned int, vector signed char);
vector unsigned int vec_sro (vector unsigned int, vector unsigned char);
vector signed short vec_sro (vector signed short, vector signed char);
vector signed short vec_sro (vector signed short, vector unsigned char);
vector unsigned short vec_sro (vector unsigned short,
vector signed char);
vector unsigned short vec_sro (vector unsigned short,
vector unsigned char);
vector signed char vec_sro (vector signed char, vector signed char);
vector signed char vec_sro (vector signed char, vector unsigned char);
vector unsigned char vec_sro (vector unsigned char, vector signed char);
vector unsigned char vec_sro (vector unsigned char,
vector unsigned char);
void vec_st (vector float, int, float *);
void vec_st (vector float, int, vector float *);
void vec_st (vector signed int, int, int *);
void vec_st (vector signed int, int, unsigned int *);
void vec_st (vector unsigned int, int, unsigned int *);
void vec_st (vector unsigned int, int, vector unsigned int *);
void vec_st (vector signed short, int, short *);
void vec_st (vector signed short, int, vector unsigned short *);
void vec_st (vector signed short, int, vector signed short *);
void vec_st (vector unsigned short, int, unsigned short *);
void vec_st (vector unsigned short, int, vector unsigned short *);
void vec_st (vector signed char, int, signed char *);
void vec_st (vector signed char, int, unsigned char *);
void vec_st (vector signed char, int, vector signed char *);
void vec_st (vector unsigned char, int, unsigned char *);
void vec_st (vector unsigned char, int, vector unsigned char *);
void vec_ste (vector signed char, int, unsigned char *);
void vec_ste (vector signed char, int, signed char *);
void vec_ste (vector unsigned char, int, unsigned char *);
void vec_ste (vector signed short, int, short *);
void vec_ste (vector signed short, int, unsigned short *);
void vec_ste (vector unsigned short, int, void *);
void vec_ste (vector signed int, int, unsigned int *);
void vec_ste (vector signed int, int, int *);
void vec_ste (vector unsigned int, int, unsigned int *);
void vec_ste (vector float, int, float *);
void vec_stl (vector float, int, vector float *);
void vec_stl (vector float, int, float *);
void vec_stl (vector signed int, int, vector signed int *);
void vec_stl (vector signed int, int, int *);
void vec_stl (vector signed int, int, unsigned int *);
void vec_stl (vector unsigned int, int, vector unsigned int *);
void vec_stl (vector unsigned int, int, unsigned int *);
void vec_stl (vector signed short, int, short *);
void vec_stl (vector signed short, int, unsigned short *);
void vec_stl (vector signed short, int, vector signed short *);
void vec_stl (vector unsigned short, int, unsigned short *);
void vec_stl (vector unsigned short, int, vector signed short *);
void vec_stl (vector signed char, int, signed char *);
void vec_stl (vector signed char, int, unsigned char *);
void vec_stl (vector signed char, int, vector signed char *);
void vec_stl (vector unsigned char, int, unsigned char *);
void vec_stl (vector unsigned char, int, vector unsigned char *);
vector signed char vec_sub (vector signed char, vector signed char);
vector unsigned char vec_sub (vector signed char, vector unsigned char);
vector unsigned char vec_sub (vector unsigned char, vector signed char);
vector unsigned char vec_sub (vector unsigned char,
vector unsigned char);
vector signed short vec_sub (vector signed short, vector signed short);
vector unsigned short vec_sub (vector signed short,
vector unsigned short);
vector unsigned short vec_sub (vector unsigned short,
vector signed short);
vector unsigned short vec_sub (vector unsigned short,
vector unsigned short);
vector signed int vec_sub (vector signed int, vector signed int);
vector unsigned int vec_sub (vector signed int, vector unsigned int);
vector unsigned int vec_sub (vector unsigned int, vector signed int);
vector unsigned int vec_sub (vector unsigned int, vector unsigned int);
vector float vec_sub (vector float, vector float);
vector unsigned int vec_subc (vector unsigned int, vector unsigned int);
vector unsigned char vec_subs (vector signed char,
vector unsigned char);
vector unsigned char vec_subs (vector unsigned char,
vector signed char);
vector unsigned char vec_subs (vector unsigned char,
vector unsigned char);
vector signed char vec_subs (vector signed char, vector signed char);
vector unsigned short vec_subs (vector signed short,
vector unsigned short);
vector unsigned short vec_subs (vector unsigned short,
vector signed short);
vector unsigned short vec_subs (vector unsigned short,
vector unsigned short);
vector signed short vec_subs (vector signed short, vector signed short);
vector unsigned int vec_subs (vector signed int, vector unsigned int);
vector unsigned int vec_subs (vector unsigned int, vector signed int);
vector unsigned int vec_subs (vector unsigned int, vector unsigned int);
vector signed int vec_subs (vector signed int, vector signed int);
vector unsigned int vec_sum4s (vector unsigned char,
vector unsigned int);
vector signed int vec_sum4s (vector signed char, vector signed int);
vector signed int vec_sum4s (vector signed short, vector signed int);
vector signed int vec_sum2s (vector signed int, vector signed int);
vector signed int vec_sums (vector signed int, vector signed int);
vector float vec_trunc (vector float);
vector signed short vec_unpackh (vector signed char);
vector unsigned int vec_unpackh (vector signed short);
vector signed int vec_unpackh (vector signed short);
vector signed short vec_unpackl (vector signed char);
vector unsigned int vec_unpackl (vector signed short);
vector signed int vec_unpackl (vector signed short);
vector float vec_xor (vector float, vector float);
vector float vec_xor (vector float, vector signed int);
vector float vec_xor (vector signed int, vector float);
vector signed int vec_xor (vector signed int, vector signed int);
vector unsigned int vec_xor (vector signed int, vector unsigned int);
vector unsigned int vec_xor (vector unsigned int, vector signed int);
vector unsigned int vec_xor (vector unsigned int, vector unsigned int);
vector signed short vec_xor (vector signed short, vector signed short);
vector unsigned short vec_xor (vector signed short,
vector unsigned short);
vector unsigned short vec_xor (vector unsigned short,
vector signed short);
vector unsigned short vec_xor (vector unsigned short,
vector unsigned short);
vector signed char vec_xor (vector signed char, vector signed char);
vector unsigned char vec_xor (vector signed char, vector unsigned char);
vector unsigned char vec_xor (vector unsigned char, vector signed char);
vector unsigned char vec_xor (vector unsigned char,
vector unsigned char);
vector signed int vec_all_eq (vector signed char, vector unsigned char);
vector signed int vec_all_eq (vector signed char, vector signed char);
vector signed int vec_all_eq (vector unsigned char, vector signed char);
vector signed int vec_all_eq (vector unsigned char,
vector unsigned char);
vector signed int vec_all_eq (vector signed short,
vector unsigned short);
vector signed int vec_all_eq (vector signed short, vector signed short);
vector signed int vec_all_eq (vector unsigned short,
vector signed short);
vector signed int vec_all_eq (vector unsigned short,
vector unsigned short);
vector signed int vec_all_eq (vector signed int, vector unsigned int);
vector signed int vec_all_eq (vector signed int, vector signed int);
vector signed int vec_all_eq (vector unsigned int, vector signed int);
vector signed int vec_all_eq (vector unsigned int, vector unsigned int);
vector signed int vec_all_eq (vector float, vector float);
vector signed int vec_all_ge (vector signed char, vector unsigned char);
vector signed int vec_all_ge (vector unsigned char, vector signed char);
vector signed int vec_all_ge (vector unsigned char,
vector unsigned char);
vector signed int vec_all_ge (vector signed char, vector signed char);
vector signed int vec_all_ge (vector signed short,
vector unsigned short);
vector signed int vec_all_ge (vector unsigned short,
vector signed short);
vector signed int vec_all_ge (vector unsigned short,
vector unsigned short);
vector signed int vec_all_ge (vector signed short, vector signed short);
vector signed int vec_all_ge (vector signed int, vector unsigned int);
vector signed int vec_all_ge (vector unsigned int, vector signed int);
vector signed int vec_all_ge (vector unsigned int, vector unsigned int);
vector signed int vec_all_ge (vector signed int, vector signed int);
vector signed int vec_all_ge (vector float, vector float);
vector signed int vec_all_gt (vector signed char, vector unsigned char);
vector signed int vec_all_gt (vector unsigned char, vector signed char);
vector signed int vec_all_gt (vector unsigned char,
vector unsigned char);
vector signed int vec_all_gt (vector signed char, vector signed char);
vector signed int vec_all_gt (vector signed short,
vector unsigned short);
vector signed int vec_all_gt (vector unsigned short,
vector signed short);
vector signed int vec_all_gt (vector unsigned short,
vector unsigned short);
vector signed int vec_all_gt (vector signed short, vector signed short);
vector signed int vec_all_gt (vector signed int, vector unsigned int);
vector signed int vec_all_gt (vector unsigned int, vector signed int);
vector signed int vec_all_gt (vector unsigned int, vector unsigned int);
vector signed int vec_all_gt (vector signed int, vector signed int);
vector signed int vec_all_gt (vector float, vector float);
vector signed int vec_all_in (vector float, vector float);
vector signed int vec_all_le (vector signed char, vector unsigned char);
vector signed int vec_all_le (vector unsigned char, vector signed char);
vector signed int vec_all_le (vector unsigned char,
vector unsigned char);
vector signed int vec_all_le (vector signed char, vector signed char);
vector signed int vec_all_le (vector signed short,
vector unsigned short);
vector signed int vec_all_le (vector unsigned short,
vector signed short);
vector signed int vec_all_le (vector unsigned short,
vector unsigned short);
vector signed int vec_all_le (vector signed short, vector signed short);
vector signed int vec_all_le (vector signed int, vector unsigned int);
vector signed int vec_all_le (vector unsigned int, vector signed int);
vector signed int vec_all_le (vector unsigned int, vector unsigned int);
vector signed int vec_all_le (vector signed int, vector signed int);
vector signed int vec_all_le (vector float, vector float);
vector signed int vec_all_lt (vector signed char, vector unsigned char);
vector signed int vec_all_lt (vector unsigned char, vector signed char);
vector signed int vec_all_lt (vector unsigned char,
vector unsigned char);
vector signed int vec_all_lt (vector signed char, vector signed char);
vector signed int vec_all_lt (vector signed short,
vector unsigned short);
vector signed int vec_all_lt (vector unsigned short,
vector signed short);
vector signed int vec_all_lt (vector unsigned short,
vector unsigned short);
vector signed int vec_all_lt (vector signed short, vector signed short);
vector signed int vec_all_lt (vector signed int, vector unsigned int);
vector signed int vec_all_lt (vector unsigned int, vector signed int);
vector signed int vec_all_lt (vector unsigned int, vector unsigned int);
vector signed int vec_all_lt (vector signed int, vector signed int);
vector signed int vec_all_lt (vector float, vector float);
vector signed int vec_all_nan (vector float);
vector signed int vec_all_ne (vector signed char, vector unsigned char);
vector signed int vec_all_ne (vector signed char, vector signed char);
vector signed int vec_all_ne (vector unsigned char, vector signed char);
vector signed int vec_all_ne (vector unsigned char,
vector unsigned char);
vector signed int vec_all_ne (vector signed short,
vector unsigned short);
vector signed int vec_all_ne (vector signed short, vector signed short);
vector signed int vec_all_ne (vector unsigned short,
vector signed short);
vector signed int vec_all_ne (vector unsigned short,
vector unsigned short);
vector signed int vec_all_ne (vector signed int, vector unsigned int);
vector signed int vec_all_ne (vector signed int, vector signed int);
vector signed int vec_all_ne (vector unsigned int, vector signed int);
vector signed int vec_all_ne (vector unsigned int, vector unsigned int);
vector signed int vec_all_ne (vector float, vector float);
vector signed int vec_all_nge (vector float, vector float);
vector signed int vec_all_ngt (vector float, vector float);
vector signed int vec_all_nle (vector float, vector float);
vector signed int vec_all_nlt (vector float, vector float);
vector signed int vec_all_numeric (vector float);
vector signed int vec_any_eq (vector signed char, vector unsigned char);
vector signed int vec_any_eq (vector signed char, vector signed char);
vector signed int vec_any_eq (vector unsigned char, vector signed char);
vector signed int vec_any_eq (vector unsigned char,
vector unsigned char);
vector signed int vec_any_eq (vector signed short,
vector unsigned short);
vector signed int vec_any_eq (vector signed short, vector signed short);
vector signed int vec_any_eq (vector unsigned short,
vector signed short);
vector signed int vec_any_eq (vector unsigned short,
vector unsigned short);
vector signed int vec_any_eq (vector signed int, vector unsigned int);
vector signed int vec_any_eq (vector signed int, vector signed int);
vector signed int vec_any_eq (vector unsigned int, vector signed int);
vector signed int vec_any_eq (vector unsigned int, vector unsigned int);
vector signed int vec_any_eq (vector float, vector float);
vector signed int vec_any_ge (vector signed char, vector unsigned char);
vector signed int vec_any_ge (vector unsigned char, vector signed char);
vector signed int vec_any_ge (vector unsigned char,
vector unsigned char);
vector signed int vec_any_ge (vector signed char, vector signed char);
vector signed int vec_any_ge (vector signed short,
vector unsigned short);
vector signed int vec_any_ge (vector unsigned short,
vector signed short);
vector signed int vec_any_ge (vector unsigned short,
vector unsigned short);
vector signed int vec_any_ge (vector signed short, vector signed short);
vector signed int vec_any_ge (vector signed int, vector unsigned int);
vector signed int vec_any_ge (vector unsigned int, vector signed int);
vector signed int vec_any_ge (vector unsigned int, vector unsigned int);
vector signed int vec_any_ge (vector signed int, vector signed int);
vector signed int vec_any_ge (vector float, vector float);
vector signed int vec_any_gt (vector signed char, vector unsigned char);
vector signed int vec_any_gt (vector unsigned char, vector signed char);
vector signed int vec_any_gt (vector unsigned char,
vector unsigned char);
vector signed int vec_any_gt (vector signed char, vector signed char);
vector signed int vec_any_gt (vector signed short,
vector unsigned short);
vector signed int vec_any_gt (vector unsigned short,
vector signed short);
vector signed int vec_any_gt (vector unsigned short,
vector unsigned short);
vector signed int vec_any_gt (vector signed short, vector signed short);
vector signed int vec_any_gt (vector signed int, vector unsigned int);
vector signed int vec_any_gt (vector unsigned int, vector signed int);
vector signed int vec_any_gt (vector unsigned int, vector unsigned int);
vector signed int vec_any_gt (vector signed int, vector signed int);
vector signed int vec_any_gt (vector float, vector float);
vector signed int vec_any_le (vector signed char, vector unsigned char);
vector signed int vec_any_le (vector unsigned char, vector signed char);
vector signed int vec_any_le (vector unsigned char,
vector unsigned char);
vector signed int vec_any_le (vector signed char, vector signed char);
vector signed int vec_any_le (vector signed short,
vector unsigned short);
vector signed int vec_any_le (vector unsigned short,
vector signed short);
vector signed int vec_any_le (vector unsigned short,
vector unsigned short);
vector signed int vec_any_le (vector signed short, vector signed short);
vector signed int vec_any_le (vector signed int, vector unsigned int);
vector signed int vec_any_le (vector unsigned int, vector signed int);
vector signed int vec_any_le (vector unsigned int, vector unsigned int);
vector signed int vec_any_le (vector signed int, vector signed int);
vector signed int vec_any_le (vector float, vector float);
vector signed int vec_any_lt (vector signed char, vector unsigned char);
vector signed int vec_any_lt (vector unsigned char, vector signed char);
vector signed int vec_any_lt (vector unsigned char,
vector unsigned char);
vector signed int vec_any_lt (vector signed char, vector signed char);
vector signed int vec_any_lt (vector signed short,
vector unsigned short);
vector signed int vec_any_lt (vector unsigned short,
vector signed short);
vector signed int vec_any_lt (vector unsigned short,
vector unsigned short);
vector signed int vec_any_lt (vector signed short, vector signed short);
vector signed int vec_any_lt (vector signed int, vector unsigned int);
vector signed int vec_any_lt (vector unsigned int, vector signed int);
vector signed int vec_any_lt (vector unsigned int, vector unsigned int);
vector signed int vec_any_lt (vector signed int, vector signed int);
vector signed int vec_any_lt (vector float, vector float);
vector signed int vec_any_nan (vector float);
vector signed int vec_any_ne (vector signed char, vector unsigned char);
vector signed int vec_any_ne (vector signed char, vector signed char);
vector signed int vec_any_ne (vector unsigned char, vector signed char);
vector signed int vec_any_ne (vector unsigned char,
vector unsigned char);
vector signed int vec_any_ne (vector signed short,
vector unsigned short);
vector signed int vec_any_ne (vector signed short, vector signed short);
vector signed int vec_any_ne (vector unsigned short,
vector signed short);
vector signed int vec_any_ne (vector unsigned short,
vector unsigned short);
vector signed int vec_any_ne (vector signed int, vector unsigned int);
vector signed int vec_any_ne (vector signed int, vector signed int);
vector signed int vec_any_ne (vector unsigned int, vector signed int);
vector signed int vec_any_ne (vector unsigned int, vector unsigned int);
vector signed int vec_any_ne (vector float, vector float);
vector signed int vec_any_nge (vector float, vector float);
vector signed int vec_any_ngt (vector float, vector float);
vector signed int vec_any_nle (vector float, vector float);
vector signed int vec_any_nlt (vector float, vector float);
vector signed int vec_any_numeric (vector float);
vector signed int vec_any_out (vector float, vector float);
|
GCC supports several types of pragmas, primarily in order to compile code originally written for other compilers. Note that in general we do not recommend the use of pragmas; See section 5.25 Declaring Attributes of Functions, for further explanation.
5.46.1 ARM Pragmas 5.46.2 RS/6000 and PowerPC Pragmas 5.46.3 Darwin Pragmas 5.46.4 Solaris Pragmas 5.46.5 Tru64 Pragmas
The ARM target defines pragmas for controlling the default addition of
long_call and short_call attributes to functions.
See section 5.25 Declaring Attributes of Functions, for information about the effects of these
attributes.
long_calls
long_call attribute.
no_long_calls
short_call attribute.
long_calls_off
long_call or short_call attributes of
subsequent functions.
The RS/6000 and PowerPC targets define one pragma for controlling
whether or not the longcall attribute is added to function
declarations by default. This pragma overrides the `-mlongcall'
option, but not the longcall and shortcall attributes.
See section 3.17.10 IBM RS/6000 and PowerPC Options, for more information about when long
calls are and are not necessary.
longcall (1)
longcall attribute to all subsequent function
declarations.
longcall (0)
longcall attribute to subsequent function
declarations.
The following pragmas are available for all architectures running the Darwin operating system. These are useful for compatibility with other Mac OS compilers.
mark tokens...
options align=alignment
mac68k, to emulate m68k alignment, or
power, to emulate PowerPC alignment. Uses of this pragma nest
properly; to restore the previous setting, use reset for the
alignment.
segment tokens...
unused (var [, var]...)
unused attribute, except that this pragma may appear
anywhere within the variables' scopes.
For compatibility with the SunPRO compiler, the following pragma is supported.
redefine_extname oldname newname
This pragma gives the C function oldname the assembler label
newname. The pragma must appear before the function declaration.
This pragma is equivalent to the asm labels extension (see section 5.37 Controlling Names Used in Assembler Code). The preprocessor defines __PRAGMA_REDEFINE_EXTNAME
if the pragma is available.
For compatibility with the Compaq C compiler, the following pragma is supported.
extern_prefix string
This pragma renames all subsequent function and variable declarations
such that string is prepended to the name. This effect may be
terminated by using another extern_prefix pragma with the
empty string.
This pragma is similar in intent to to the asm labels extension
(see section 5.37 Controlling Names Used in Assembler Code) in that the system programmer wants to change
the assembly-level ABI without changing the source-level API. The
preprocessor defines __PRAGMA_EXTERN_PREFIX if the pragma is
available.
For compatibility with other compilers, GCC allows you to define a structure or union that contains, as fields, structures and unions without names. For example:
struct {
int a;
union {
int b;
float c;
};
int d;
} foo;
|
In this example, the user would be able to access members of the unnamed
union with code like `foo.b'. Note that only unnamed structs and
unions are allowed, you may not have, for example, an unnamed
int.
You must never create such structures that cause ambiguous field definitions. For example, this structure:
struct {
int a;
struct {
int a;
};
} foo;
|
It is ambiguous which a is being referred to with `foo.a'.
Such constructs are not supported and must be avoided. In the future,
such constructs may be detected and treated as compilation errors.
Thread-local storage (TLS) is a mechanism by which variables
are allocated such that there is one instance of the variable per extant
thread. The run-time model GCC uses to implement this originates
in the IA-64 processor-specific ABI, but has since been migrated
to other processors as well. It requires significant support from
the linker (ld), dynamic linker (ld.so), and
system libraries (`libc.so' and `libpthread.so'), so it
is not available everywhere.
At the user level, the extension is visible with a new storage
class keyword: __thread. For example:
__thread int i; extern __thread struct state s; static __thread char *p; |
The __thread specifier may be used alone, with the extern
or static specifiers, but with no other storage class specifier.
When used with extern or static, __thread must appear
immediately after the other storage class specifier.
The __thread specifier may be applied to any global, file-scoped
static, function-scoped static, or static data member of a class. It may
not be applied to block-scoped automatic or non-static data member.
When the address-of operator is applied to a thread-local variable, it is evaluated at run-time and returns the address of the current thread's instance of that variable. An address so obtained may be used by any thread. When a thread terminates, any pointers to thread-local variables in that thread become invalid.
No static initialization may refer to the address of a thread-local variable.
In C++, if an initializer is present for a thread-local variable, it must be a constant-expression, as defined in 5.19.2 of the ANSI/ISO C++ standard.
See ELF Handling For Thread-Local Storage for a detailed explanation of the four thread-local storage addressing models, and how the run-time is expected to function.
5.48.1 ISO/IEC 9899:1999 Edits for Thread-Local Storage 5.48.2 ISO/IEC 14882:1998 Edits for Thread-Local Storage
The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that document the exact semantics of the language extension.
Add new text after paragraph 1
Within either execution environment, a thread is a flow of control within a program. It is implementation defined whether or not there may be more than one thread associated with a program. It is implementation defined how threads beyond the first are created, the name and type of the function called at thread startup, and how threads may be terminated. However, objects with thread storage duration shall be initialized before thread startup.
Add new text before paragraph 3
An object whose identifier is declared with the storage-class
specifier __thread has thread storage duration.
Its lifetime is the entire execution of the thread, and its
stored value is initialized only once, prior to thread startup.
Add __thread.
Add __thread to the list of storage class specifiers in
paragraph 1.
Change paragraph 2 to
With the exception of__thread, at most one storage-class specifier may be given [...]. The__threadspecifier may be used alone, or immediately followingexternorstatic.
Add new text after paragraph 6
The declaration of an identifier for a variable that has block scope that specifies__threadshall also specify eitherexternorstatic.The
__threadspecifier shall be used only with variables.
The following are a set of changes to ISO/IEC 14882:1998 (aka C++98) that document the exact semantics of the language extension.
New text after paragraph 4
A thread is a flow of control within the abstract machine. It is implementation defined whether or not there may be more than one thread.
New text after paragraph 7
It is unspecified whether additional action must be taken to ensure when and whether side effects are visible to other threads.
Add __thread.
Add after paragraph 5
The thread that begins execution at themainfunction is called the main thread. It is implementation defined how functions beginning threads other than the main thread are designated or typed. A function so designated, as well as themainfunction, is called a thread startup function. It is implementation defined what happens if a thread startup function returns. It is implementation defined what happens to other threads when any thread callsexit.
Add after paragraph 4
The storage for an object of thread storage duration shall be statically initialized before the first statement of the thread startup function. An object of thread storage duration shall not require dynamic initialization.
Add after paragraph 3
The type of an object with thread storage duration shall not have a non-trivial destructor, nor shall it be an array type whose elements (directly or indirectly) have non-trivial destructors.
Add "thread storage duration" to the list in paragraph 1.
Change paragraph 2
Thread, static, and automatic storage durations are associated with objects introduced by declarations [...].
Add __thread to the list of specifiers in paragraph 3.
New section before [basic.stc.static]
The keyword__threadapplied to a non-local object gives the object thread storage duration.A local variable or class data member declared both
staticand__threadgives the variable or member thread storage duration.
Change paragraph 1
All objects which have neither thread storage duration, dynamic storage duration nor are local [...].
Add __thread to the list in paragraph 1.
Change paragraph 1
With the exception of__thread, at most one storage-class-specifier shall appear in a given decl-specifier-seq. The__threadspecifier may be used alone, or immediately following theexternorstaticspecifiers. [...]
Add after paragraph 5
The __thread specifier can be applied only to the names of objects
and to anonymous unions.
Add after paragraph 6
Non-staticmembers shall not be__thread.
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