[PATCH] PR ld/17975: Useless FILE entry in symbol table for linker generated symbols

[H.J. Lu]

On Sun, Feb 15, 2015 at 5:04 PM, Alan Modra <amodra@gmail.com> wrote:
> On Sun, Feb 15, 2015 at 10:46:02AM -0800, H.J. Lu wrote:
>> We output a NULL STT_FILE symbol for forced local symbols so that they
>> are not associated with the STT_FILE symbol for real local symbols. This
>> patch makes sure that the NULL STT_FILE symbol is placed before forced
>> local symbols.  OK for trunk?  I will update other expected outputs
>> after this patch has been checked in.
>
> Huh, silly me for not noticing that forced local symbols can currently
> be associated with the wrong file.  Hmm, they do of course belong with
> a particular file.  So...
>
> We could keep the file association, and do away with the NULL STT_FILE
> file symbol:
> - In elf_link_input_bfd, replace all calls to elf_link_output_sym
>   with another function that buffers up local symbols to an array
>   attached to the input bfd (I think outsymbols should be free for
>   this use).
> - In bfd_elf_final_link, output the first all-zero symbol and section
>   symbols, then follow that with a pass over globals emitting the
>   forced-local symbols not associated with an input file (ie. those we
>   currently output on the second pass), and buffering up other
>   forced-local symbols to their input bfd.  Then loop over input bfds
>   emitting the buffered local symbols.  An input bfd with locals but
>   no initial STT_FILE symbol needs one to be added.  An input bfd with
>   more than one STT_FILE symbol (ie. specifying more than one source
>   file) needs to have another STT_FILE symbol added before the
>   forced-local globals.
> - Finally, output global symbols.
>
> How does that sound?  Let me know if you're interested in implementing
> this.  If not, I'll find time this week.
>

There are a couple issues:

1. If the forced local symbols aren't sorted by input file, we may
generate many redundant STT_FILE symbols.
2. When the forced local symbols are sorted by input file, we still
generate one STT_FILE symbol per input file with forced local
symbols.  We may wind with many STT_FILE symbols.  You can
try it on glibc and libstdc++.

In any case, how useful are they?  Are they really needed?
FWIW, gold doesn't generate any those  STT_FILE symbols.


-- 
H.J.