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3. objcopy

 
objcopy [`-F' bfdname|`--target='bfdname]
        [`-I' bfdname|`--input-target='bfdname]
        [`-O' bfdname|`--output-target='bfdname]
        [`-B' bfdarch|`--binary-architecture='bfdarch]
        [`-S'|`--strip-all']
        [`-g'|`--strip-debug']
        [`-K' symbolname|`--keep-symbol='symbolname]
        [`-N' symbolname|`--strip-symbol='symbolname]
        [`-G' symbolname|`--keep-global-symbol='symbolname]
        [`-L' symbolname|`--localize-symbol='symbolname]
        [`-W' symbolname|`--weaken-symbol='symbolname]
        [`-w'|`--wildcard']
        [`-x'|`--discard-all']
        [`-X'|`--discard-locals']
        [`-b' byte|`--byte='byte]
        [`-i' interleave|`--interleave='interleave]
        [`-j' sectionname|`--only-section='sectionname]
        [`-R' sectionname|`--remove-section='sectionname]
        [`-p'|`--preserve-dates']
        [`--debugging']
        [`--gap-fill='val]
        [`--pad-to='address]
        [`--set-start='val]
        [`--adjust-start='incr]
        [`--change-addresses='incr]
        [`--change-section-address' section{=,+,-}val]
        [`--change-section-lma' section{=,+,-}val]
        [`--change-section-vma' section{=,+,-}val]
        [`--change-warnings'] [`--no-change-warnings']
        [`--set-section-flags' section=flags]
        [`--add-section' sectionname=filename]
        [`--rename-section' oldname=newname[,flags]]
        [`--change-leading-char'] [`--remove-leading-char']
        [`--srec-len='ival] [`--srec-forceS3']
        [`--redefine-sym' old=new]
        [`--redefine-syms='filename]
        [`--weaken']
        [`--keep-symbols='filename]
        [`--strip-symbols='filename]
        [`--keep-global-symbols='filename]
        [`--localize-symbols='filename]
        [`--weaken-symbols='filename]
        [`--alt-machine-code='index]
        [`--prefix-symbols='string]
        [`--prefix-sections='string]
        [`--prefix-alloc-sections='string]
        [`--add-gnu-debuglink='path-to-file]
        [`--only-keep-debug']
        [`--writable-text']
        [`--readonly-text']
        [`--pure']
        [`--impure']
        [`-v'|`--verbose']
        [`-V'|`--version']  
        [`--help'] [`--info']
        infile [outfile]

The GNU objcopy utility copies the contents of an object file to another. objcopy uses the GNU BFD Library to read and write the object files. It can write the destination object file in a format different from that of the source object file. The exact behavior of objcopy is controlled by command-line options. Note that objcopy should be able to copy a fully linked file between any two formats. However, copying a relocatable object file between any two formats may not work as expected.

objcopy creates temporary files to do its translations and deletes them afterward. objcopy uses BFD to do all its translation work; it has access to all the formats described in BFD and thus is able to recognize most formats without being told explicitly. See section `BFD' in Using LD.

objcopy can be used to generate S-records by using an output target of `srec' (e.g., use `-O srec').

objcopy can be used to generate a raw binary file by using an output target of `binary' (e.g., use `-O binary'). When objcopy generates a raw binary file, it will essentially produce a memory dump of the contents of the input object file. All symbols and relocation information will be discarded. The memory dump will start at the load address of the lowest section copied into the output file.

When generating an S-record or a raw binary file, it may be helpful to use `-S' to remove sections containing debugging information. In some cases `-R' will be useful to remove sections which contain information that is not needed by the binary file.

Note---objcopy is not able to change the endianness of its input files. If the input format has an endianness (some formats do not), objcopy can only copy the inputs into file formats that have the same endianness or which have no endianness (e.g., `srec').

infile
outfile
The input and output files, respectively. If you do not specify outfile, objcopy creates a temporary file and destructively renames the result with the name of infile.

-I bfdname
--input-target=bfdname
Consider the source file's object format to be bfdname, rather than attempting to deduce it. See section 15.1 Target Selection, for more information.

-O bfdname
--output-target=bfdname
Write the output file using the object format bfdname. See section 15.1 Target Selection, for more information.

-F bfdname
--target=bfdname
Use bfdname as the object format for both the input and the output file; i.e., simply transfer data from source to destination with no translation. See section 15.1 Target Selection, for more information.

-B bfdarch
--binary-architecture=bfdarch
Useful when transforming a raw binary input file into an object file. In this case the output architecture can be set to bfdarch. This option will be ignored if the input file has a known bfdarch. You can access this binary data inside a program by referencing the special symbols that are created by the conversion process. These symbols are called _binary_objfile_start, _binary_objfile_end and _binary_objfile_size. e.g. you can transform a picture file into an object file and then access it in your code using these symbols.

-j sectionname
--only-section=sectionname
Copy only the named section from the input file to the output file. This option may be given more than once. Note that using this option inappropriately may make the output file unusable.

-R sectionname
--remove-section=sectionname
Remove any section named sectionname from the output file. This option may be given more than once. Note that using this option inappropriately may make the output file unusable.

-S
--strip-all
Do not copy relocation and symbol information from the source file.

-g
--strip-debug
Do not copy debugging symbols or sections from the source file.

--strip-unneeded
Strip all symbols that are not needed for relocation processing.

-K symbolname
--keep-symbol=symbolname
Copy only symbol symbolname from the source file. This option may be given more than once.

-N symbolname
--strip-symbol=symbolname
Do not copy symbol symbolname from the source file. This option may be given more than once.

-G symbolname
--keep-global-symbol=symbolname
Keep only symbol symbolname global. Make all other symbols local to the file, so that they are not visible externally. This option may be given more than once.

-L symbolname
--localize-symbol=symbolname
Make symbol symbolname local to the file, so that it is not visible externally. This option may be given more than once.

-W symbolname
--weaken-symbol=symbolname
Make symbol symbolname weak. This option may be given more than once.

-w
--wildcard
Permit regular expressions in symbolnames used in other command line options. The question mark (?), asterisk (*), backslash (\) and square brackets ([]) operators can be used anywhere in the symbol name. If the first character of the symbol name is the exclamation point (!) then the sense of the switch is reversed for that symbol. For example:

 
  -w -W !foo -W fo*

would cause objcopy to weaken all symbols that start with "fo" except for the symbol "foo".

-x
--discard-all
Do not copy non-global symbols from the source file.

-X
--discard-locals
Do not copy compiler-generated local symbols. (These usually start with `L' or `.'.)

-b byte
--byte=byte
Keep only every byteth byte of the input file (header data is not affected). byte can be in the range from 0 to interleave-1, where interleave is given by the `-i' or `--interleave' option, or the default of 4. This option is useful for creating files to program ROM. It is typically used with an srec output target.

-i interleave
--interleave=interleave
Only copy one out of every interleave bytes. Select which byte to copy with the `-b' or `--byte' option. The default is 4. objcopy ignores this option if you do not specify either `-b' or `--byte'.

-p
--preserve-dates
Set the access and modification dates of the output file to be the same as those of the input file.

--debugging
Convert debugging information, if possible. This is not the default because only certain debugging formats are supported, and the conversion process can be time consuming.

--gap-fill val
Fill gaps between sections with val. This operation applies to the load address (LMA) of the sections. It is done by increasing the size of the section with the lower address, and filling in the extra space created with val.

--pad-to address
Pad the output file up to the load address address. This is done by increasing the size of the last section. The extra space is filled in with the value specified by `--gap-fill' (default zero).

--set-start val
Set the start address of the new file to val. Not all object file formats support setting the start address.

--change-start incr
--adjust-start incr
Change the start address by adding incr. Not all object file formats support setting the start address.

--change-addresses incr
--adjust-vma incr
Change the VMA and LMA addresses of all sections, as well as the start address, by adding incr. Some object file formats do not permit section addresses to be changed arbitrarily. Note that this does not relocate the sections; if the program expects sections to be loaded at a certain address, and this option is used to change the sections such that they are loaded at a different address, the program may fail.

--change-section-address section{=,+,-}val
--adjust-section-vma section{=,+,-}val
Set or change both the VMA address and the LMA address of the named section. If `=' is used, the section address is set to val. Otherwise, val is added to or subtracted from the section address. See the comments under `--change-addresses', above. If section does not exist in the input file, a warning will be issued, unless `--no-change-warnings' is used.

--change-section-lma section{=,+,-}val
Set or change the LMA address of the named section. The LMA address is the address where the section will be loaded into memory at program load time. Normally this is the same as the VMA address, which is the address of the section at program run time, but on some systems, especially those where a program is held in ROM, the two can be different. If `=' is used, the section address is set to val. Otherwise, val is added to or subtracted from the section address. See the comments under `--change-addresses', above. If section does not exist in the input file, a warning will be issued, unless `--no-change-warnings' is used.

--change-section-vma section{=,+,-}val
Set or change the VMA address of the named section. The VMA address is the address where the section will be located once the program has started executing. Normally this is the same as the LMA address, which is the address where the section will be loaded into memory, but on some systems, especially those where a program is held in ROM, the two can be different. If `=' is used, the section address is set to val. Otherwise, val is added to or subtracted from the section address. See the comments under `--change-addresses', above. If section does not exist in the input file, a warning will be issued, unless `--no-change-warnings' is used.

--change-warnings
--adjust-warnings
If `--change-section-address' or `--change-section-lma' or `--change-section-vma' is used, and the named section does not exist, issue a warning. This is the default.

--no-change-warnings
--no-adjust-warnings
Do not issue a warning if `--change-section-address' or `--adjust-section-lma' or `--adjust-section-vma' is used, even if the named section does not exist.

--set-section-flags section=flags
Set the flags for the named section. The flags argument is a comma separated string of flag names. The recognized names are `alloc', `contents', `load', `noload', `readonly', `code', `data', `rom', `share', and `debug'. You can set the `contents' flag for a section which does not have contents, but it is not meaningful to clear the `contents' flag of a section which does have contents--just remove the section instead. Not all flags are meaningful for all object file formats.

--add-section sectionname=filename
Add a new section named sectionname while copying the file. The contents of the new section are taken from the file filename. The size of the section will be the size of the file. This option only works on file formats which can support sections with arbitrary names.

--rename-section oldname=newname[,flags]
Rename a section from oldname to newname, optionally changing the section's flags to flags in the process. This has the advantage over usng a linker script to perform the rename in that the output stays as an object file and does not become a linked executable.

This option is particularly helpful when the input format is binary, since this will always create a section called .data. If for example, you wanted instead to create a section called .rodata containing binary data you could use the following command line to achieve it:

 
  objcopy -I binary -O <output_format> -B <architecture> \
   --rename-section .data=.rodata,alloc,load,readonly,data,contents \
   <input_binary_file> <output_object_file>

--change-leading-char
Some object file formats use special characters at the start of symbols. The most common such character is underscore, which compilers often add before every symbol. This option tells objcopy to change the leading character of every symbol when it converts between object file formats. If the object file formats use the same leading character, this option has no effect. Otherwise, it will add a character, or remove a character, or change a character, as appropriate.

--remove-leading-char
If the first character of a global symbol is a special symbol leading character used by the object file format, remove the character. The most common symbol leading character is underscore. This option will remove a leading underscore from all global symbols. This can be useful if you want to link together objects of different file formats with different conventions for symbol names. This is different from `--change-leading-char' because it always changes the symbol name when appropriate, regardless of the object file format of the output file.

--srec-len=ival
Meaningful only for srec output. Set the maximum length of the Srecords being produced to ival. This length covers both address, data and crc fields.

--srec-forceS3
Meaningful only for srec output. Avoid generation of S1/S2 records, creating S3-only record format.

--redefine-sym old=new
Change the name of a symbol old, to new. This can be useful when one is trying link two things together for which you have no source, and there are name collisions.

--redefine-syms=filename
Apply `--redefine-sym' to each symbol pair "old new" listed in the file filename. filename is simply a flat file, with one symbol pair per line. Line comments may be introduced by the hash character. This option may be given more than once.

--weaken
Change all global symbols in the file to be weak. This can be useful when building an object which will be linked against other objects using the `-R' option to the linker. This option is only effective when using an object file format which supports weak symbols.

--keep-symbols=filename
Apply `--keep-symbol' option to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once.

--strip-symbols=filename
Apply `--strip-symbol' option to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once.

--keep-global-symbols=filename
Apply `--keep-global-symbol' option to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once.

--localize-symbols=filename
Apply `--localize-symbol' option to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once.

--weaken-symbols=filename
Apply `--weaken-symbol' option to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once.

--alt-machine-code=index
If the output architecture has alternate machine codes, use the indexth code instead of the default one. This is useful in case a machine is assigned an official code and the tool-chain adopts the new code, but other applications still depend on the original code being used.

--writable-text
Mark the output text as writable. This option isn't meaningful for all object file formats.

--readonly-text
Make the output text write protected. This option isn't meaningful for all object file formats.

--pure
Mark the output file as demand paged. This option isn't meaningful for all object file formats.

--impure
Mark the output file as impure. This option isn't meaningful for all object file formats.

--prefix-symbols=string
Prefix all symbols in the output file with string.

--prefix-sections=string
Prefix all section names in the output file with string.

--prefix-alloc-sections=string
Prefix all the names of all allocated sections in the output file with string.

--add-gnu-debuglink=path-to-file
Creates a .gnu_debuglink section which contains a reference to path-to-file and adds it to the output file.

--only-keep-debug
Strip a file, removing any sections that would be stripped by `--strip-debug' and leaving the debugging sections.

The intention is that this option will be used in conjunction with `--add-gnu-debuglink' to create a two part executable. One a stripped binary which will occupy less space in RAM and in a distribution and the second a debugging information file which is only needed if debugging abilities are required. The suggested procedure to create these files is as follows:

  1. Link the executable as normal. Assuming that is is called foo then...
  2. Run objcopy --only-keep-debug foo foo.dbg to create a file containing the debugging info.
  3. Run objcopy --strip-debug foo to create a stripped executable.
  4. Run objcopy --add-gnu-debuglink=foo.dbg foo to add a link to the debugging info into the stripped executable.

Note - the choice of .dbg as an extension for the debug info file is arbitrary. Also the --only-keep-debug step is optional. You could instead do this:

  1. Link the executable as normal.
  2. Copy foo to foo.full
  3. Run objcopy --strip-debug foo
  4. Run objcopy --add-gnu-debuglink=foo.full foo

ie the file pointed to by the `--add-gnu-debuglink' can be the full executable. It does not have to be a file created by the `--only-keep-debug' switch.

-V
--version
Show the version number of objcopy.

-v
--verbose
Verbose output: list all object files modified. In the case of archives, `objcopy -V' lists all members of the archive.

--help
Show a summary of the options to objcopy.

--info
Display a list showing all architectures and object formats available.

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