Re: porting gas (&gcc)

[Nick Clifton]

Hi Alun,

> I've been searching for some documentation on the porting of gas,
> similar to that for gcc, but with no luck.
> 
> Are there any documents that you can direct me to, to guide the
> process of writing a new backend for out processor?

Sadly there is very little documentation at all. :-(  Of course if
you feel like  writing up your experiences and starting some
documentation that would be great.

You should look at the files in gas/doc.  In particular as.texinfo
covers the basics of the interface that GAS provides to the world and
internals.texi is *supposed* to be a porting guide, but it is rather
out of date.

Most people work by copying an already existing port and then
modifying it to suit their needs.  Since yours in a 16bit processor I
would suggest looking at the SH port which is also 16bit.

Basically you will need to create these files.  (Replace FOO with the
name of your chip):

  gas/config/tc-FOO.h           - Customisation of generic parts of the 
assembler
  gas/config/tc-FOO.c           - Port specific parts of the assembler
  include/{coff|elf}/FOO.h      - Port specific header file
  include/opcodes/FOO.h         - Port specific ISA encoding
  opcodes/FOO-dis.c             - Port specific disassembler routines
  opcodes/FOO-opc.c             - Port specific ISA encoding
  bfd/{elf32|coff}-FOO.c        - Port specific relocation handlers
  bfd/cpu-FOO.c                 - Port specific description of the CPU
  ld/scripttempl/FOO.sc         - Port specific linker template file
  ld/emulparam/FOO.sh           - Port specific linker customisation

You will also need to add support for your chip to the various
configuration files:

  gas/configure.in
  opcodes/configure.in
  bfd/configure.in
  bfd/config.bfd
  bfd/archures.c
  bfd/reloc.c
  ld/configure.in
  ld/configure.tgt
  include/dis-asm.h

You might like to consider using the CGEN program which is capable of
generating most of the assembler, disassembler and simulator from a
single cpu description file.  The sources for this program are
included in the binutils CVS repository.  The directory cgen/doc
contains documentation for this program.

Cheers
        Nick