> if only porting gas, besides writting tc-foo.c, which
> bfd target vector functions and bfd backend functions
> in elf32-foo.c must be implemented?
To port gas, you only need the backend vectors which are used to write
a file. You don't need the ones used to read a file. In general, you
need BFD_JUMP_TABLE_GENERIC, bfd_reloc_type_lookup,