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Re: RFA: Skip ARM ELF Mapping symbols when showing disassembly
- From: Nick Clifton <nickc at redhat dot com>
- To: Richard dot Earnshaw at arm dot com
- Cc: gdb-patches at sources dot redhat dot com, binutils at sources dot redhat dot com
- Date: Tue, 20 Jan 2004 13:23:49 +0000
- Subject: Re: RFA: Skip ARM ELF Mapping symbols when showing disassembly
- References: <m3he181gxc.fsf@redhat.com><200311131445.hADEj7C19503@pc960.cambridge.arm.com><20040114234206.GA7504@nevyn.them.org>
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