Re: RFA: Skip ARM ELF Mapping symbols when showing disassembly

[Nick Clifton <nickc@redhat.com>]

Hi Guys,

> Daniel Jacobowitz <drow@mvista.com> writes:

>> I wonder whether a better way to handle all this is to override 
>> slurp_symbol_table for arm-elf to a routine that just skips the mapping 
>> symbols entirely (or at least, doesn't put them into the list that it 
>> passes back to its caller), then to add a separate function to slurp the 
>> mapping symbols independently.  Then gdb and the disassembler (and the 
>> linker error reports) would all just work normally.
>> 
>> It would be necessary to add support for copying and fixing up the mapping 
>> symbols when linking, but that's probably not too hard.
>
> Actually, I think it's not necessary, since elf_link_input_bfd doesn't
> use the slurp routines anyway - it parses the ELF symbol table
> directly.  In testing it appears to work.
>
> There is another problem, though.  The symbols are in the symbol table
> and thus have assigned numbers.  The returned list of symbols is passed
> back to functions like bfd_canonicalize_reloc, which use the list of
> symbols to resolve relocations.  Probably other consumers assume the
> whole list of ELF symbols is returned, also, and index it by other
> copies of the symbol index.  So the linker doesn't appear to care, but
> objdump and possibly GDB do.
>
> Any ideas on how to resolve this?  We can't NULL out the mapping
> symbols in symptrs either, because the list is defined to be
> NULL-terminated (even though we return its length...).

How about providing a new BFD function which allows the caller to
determine if a symbol should be ignored ?  This function would call
through to an architecture specific backend routine if necessary,
although a generic routine which never ignored any symbols would be
the default.

We might even generalise the function to take a third argument (apart
from the bfd and the symbol) which is a bit-field defining the proposed
purpose(s) for the symbol and then have the function determine if it
is suitable.  ie something like this:

  enum { not_suitable; partially_suitable; fully_suitable } bfd_suitability;

  #define bfd_purpose_display (1 << 0)  /* Should the symbol be shown to the user ?  */
  #define bfd_purpose_resolve (1 << 1)  /* Should the symbol be used for resolving relocs ?  */
  
  extern bfd_suitability
  bfd_symbol_suits_purpose (bfd *         the_bfd,
                            bfd_symbol *  the_symbol,
                            unsigned      the_purposes);

Cheers
        Nick