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Re: [PATCH 4/n] OpenMP 4.0 offloading infrastructure: lto-wrapper


On Tue, Oct 14, 2014 at 02:42:47AM +0400, Ilya Verbin wrote:
> > For that I guess
> > lhd_begin_section
> > would need to replace:
> >   section = get_section (name, SECTION_DEBUG, NULL);
> > with:
> >   section = get_section (name, SECTION_DEBUG | SECTION_EXCLUDE, NULL);
> > either just for the .gnu.offload_lto prefixed section, or all.
> > The question is what will old assemblers and/or linkers do with that, and
> > if there are any that support linker plugins, but not SHF_EXCLUDE.
> 
> I've tried to set SECTION_EXCLUDE bit with as+ld version 2.20.51 and got a lot
> of warnings like:
> 
> /tmp/ccg7P7iS.s:2: Warning: entity size for SHF_MERGE not specified
> /tmp/ccg7P7iS.s:2: Warning: group name for SHF_GROUP not specified
> as: /tmp/ccKFKXfc.o: warning: sh_link not set for section `.gnu.lto_main.11d9780ff2ebf166'
> /usr/bin/ld: /tmp/ccKFKXfc.o: warning: sh_link not set for section `.gnu.lto_main.11d9780ff2ebf166'
> 
> I think, it can be placed under such ifdef:
> 
> #if defined (HAVE_SECTION_EXCLUDE) && HAVE_SECTION_EXCLUDE == 1
>   section = get_section (name, SECTION_DEBUG | SECTION_EXCLUDE, NULL);
> #else
>   section = get_section (name, SECTION_DEBUG, NULL);
> #endif
> 
> Currently there is HAVE_GAS_SECTION_EXCLUDE implemented in gcc/configure.ac, and
> HAVE_SECTION_EXCLUDE can use it + check a version of the linker.

My preference would be to add the | SECTION_EXCLUDE unconditionally, and
instead guard the
  if (flags & SECTION_EXCLUDE)
    *f++ = 'e';
in varasm.c (default_elf_asm_named_section).  The only other user of
SECTION_EXCLUDE seems to be -gsplit-dwarf right now, Cary, is such a change
ok with you?

If you have new gas and old linker, I'd expect it would just ignore
SHF_EXCLUDE.

	Jakub


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