The GNU binutils contain the assembler, linker, archiver and many other utilities. These utilities use various format for object files including ELF-32, Motorola S-records, Intel HEX records, and others.

1. Description of the Port

This section gives some information about the port itself.

1.1 Object Files

Gas generates object files in the ELF format. The specific tags EM_68HC11 (70) and EM_68HC12 (53) are used to identify the machine. These tags are defined by the Motorola Embedded Working Group (see Eabi WG). Gas generates the following relocation types:

• 8-bit PCREL
• 8-bit absolute
• 8-bit low address part (no complain on overflow)
• 8-bit high address part
• 16-bit PCREL
• 16-bit absolute
• branch instruction marks

1.2 Sections

Section	Description
.text	This is the standard text section for code program. By default, the linker places the text at 0x8000. This can be overridden with -Ttext option.
.rodata	This is the standard read-only data section. It is placed after the text section by the linker.
.data	This is the standard data section.
.bss	This is the standard bss section. It appears after the data section.
.page0	This is a specific section for the 68HC1x to represent the page 0. It is intended to be used to help in specifying data which are defined in the first 256-bytes (page 0) of the address space. It is placed at address 0 by the linker. It is treated as a .data section.
.eeprom	This is a specific section for the 68HC1x to represent the internal EEPROM.
.install[0-4]	These sections represent some initialization sections. They are used by the GCC startup code. Some of them are for used by applications. During the final link, these sections are merged with the .text section, and are put at beginning. Therefore, they appear at beginning of ROM area. The .install0 is reserved. It initializes the stack pointer. The .install1 is a placeholder for applications. The .install2 is reserved. It initializes the bss and data sections. The .install3 is a placeholder for applications. The .install4 is reserved and invokes the main.
.fini[0-4]	These sections represent some termination sections. They are used by the GCC finish code (exit). Some of them are for used by applications. During the final link, these sections are merged with the .text section. .fini0 and .fini4 are reserved. .fini1 is a placeholder for applications. It can contain code which is executed during exit and before the C++ static destructors. .fini2 is reserved and corresponds to the C++ static destructors. .fini3 is a placeholder for applications. This code is executed after the C++ static destructors are called. The .fini4 is reserved and corresponds to the runtime exit.
.vectors	This is a specific section for the 68HC1x to represent the vectors table. By default the vectors table is located at 0xffc0 and placed at that address by the linker. By using the -defsym vectors_addr=addr linker option, it is possible to set another address for the vectors table. For example, -defsym vectors_addr=0xbfc0 sets the vectors table at 0xbfc0.
.softregs	This is a specific section for the 68HC1x to hold the gcc soft registers. For 68HC11, this section is put during the final link in the .page0 section. For 68HC12, it is put in the .bss section.
others	Several standard sections exists for DWARF-2 debugging info, stack frame unwinding description and so on.

1.4 Linker Memory Banks

The Linker contains built-in linker scripts which indicate how to perform the link and where to put the different sections. You can use the provided linker scripts or write yours. In general, you will want to give the linker some information about the ROM and RAM you have on your board. The Linker defines two emulations which allow you to use one

The m68hc11elf and m68hc12elf emulations define the memory as follows:

  MEMORY
  {
    page0 (rwx) : ORIGIN = 0x0, LENGTH = 256
    text  (rx)  : ORIGIN = 0x08000, LENGTH = 0x8000
    data        : ORIGIN = 0x01100, LENGTH = 0x6F00
    eeprom      : ORIGIN = 0xb600, LENGTH = 512
  }
  PROVIDE (_stack = 0x1100 + 0x6f00 - 1);

which means that there are two RAM banks, one at [0x0..0xff] and one at [0x1100..0x7fff]. There is also a ROM bank at [0x8000..0xffff]. The PROVIDE instruction defines the address of the top of the stack to the top of the RAM. This memory configuration is suitable for the 68HC1x simulator. It was defined like this to be able to run the GCC test-suite.

The m68hc11elfb and m68hc12elfb emulations are the same except that they include a file memory.x that you must provide in the current directory or in one of the -L directories. The file you have to write must contain the above MEMORY definition. You can change the address and sizes of the different memory banks. You must also define the address of the top of the stack.

To select a particular linker emulation, use the -m emulation option. If you use m6811-elf-gcc or m6812-elf-gcc, you must pass the emulation through the -Xlinker or -Wl option. For example:

  m6811-elf-gcc -Wl,-m,m68hc11elfb -o tst.out tst.o

1.5 Ld Symbols

The Linker uses and provides some symbols that you can use in your program.

Symbol	Description
_start	This symbol represents the entry point of the program. It is provided by the GCC startup file and it is used by the linker to know the entry point of the program. The linker script is configured to try to put this symbol at beginning of the ROM area.
_stack	This symbol represents the top of the stack. It is computed by the linker to refer to the top of the data memory bank. The GCC startup file sets the stack pointer to this value at beginning.
etext	This symbol represents the end address of the .text section.
edata	This symbol represents the end address of the .data section.
__data_image	This symbol represents the starting address of the ROM area which contains the copy of initialized data. These data must be copied from ROM to RAM during initialization. This is done by the GCC startup file.
__data_image_end	This symbol is: __data_image + __data_section_size.
__data_section_start	This symbol represents the starting address of the data section in RAM. This symbol should rather be named: __data_start.
__data_section_size	This symbol represents the size in bytes of the data section that must be copied from ROM to RAM. This symbol should rather be named: __data_size.
__bss_start	This symbol represents the starting address of the BSS section in RAM. This is also the end of the data section.
__bss_size	This symbol represents the size in bytes of the BSS section. Together with __bss_start it is used to initialize the BSS section at startup time.
_end	This symbol represents the ending address of the BSS section in RAM.
_vectors_addr	This symbol represents the starting address of the 68HC11 vector's table. The default value is 0xffc0. If you have provided a -defsym vectors_addr=addr option to the linker, this symbol will have the value you have specified. Note: If you provide a vectors_addr symbol, there will be two symbols: one with _ and one without.

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