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Re: Long linking time
- From: Alan Modra <amodra at bigpond dot net dot au>
- To: Nicolas Savoire <nicos at maunakeatech dot com>
- Cc: binutils at sourceware dot org
- Date: Thu, 3 Aug 2006 19:56:56 +0930
- Subject: Re: Long linking time
- References: <email@example.com>
On Thu, Aug 03, 2006 at 11:06:18AM +0200, Nicolas Savoire wrote:
> I don't know if this is a gcc or ld issue, but since I updated gcc to 4.1.1
> version, the linking times of the project I work on have skyrocketted. One
> particular shared library, which used to link in less than a second now takes
> 6 minutes to link!!!! This library instantiates a lot of templates (use of
> itk image library and boost).
> After further investigation, it appears that disabling debug info generation
> during compilation or asking ld to strip debug info (-S flag) leads to normal
> linking time (~1s).
> I use binutils 2.17, but versions 2.15 and 2.16 exhibit the same behaviour.
> A quick profiling show that almost all the execution time is spent in qsort,
> the call stack at that point looks like:
> #0 elf_sort_elf_symbol (arg1=0x99e49d0, arg2=0x99eb618) at elf.c:8524
> #1 0xb7eb5ddb in bsearch () from /lib/libc.so.6
> #2 0xb7eb5f3a in qsort () from /lib/libc.so.6
> #3 0x0809fbfc in bfd_elf_match_symbols_in_sections (sec1=0x81889e4,
> sec2=0x83aa974) at elf.c:8628
> #4 0x080ac0a1 in match_group_member (sec=0x83aa974, group=0x817ad2c) at
> #5 0x080ac113 in _bfd_elf_check_kept_section (sec=0x83aa974) at
> #6 0x080acca0 in elf_link_input_bfd (finfo=0xbffe0684, input_bfd=0x81528c0)
> at elflink.c:7155
> #7 0x080af013 in bfd_elf_final_link (abfd=0x8133128, info=0x8126920) at
> #8 0x0805f39f in ldwrite () at ldwrite.c:557
> #9 0x0805c6ec in main (argc=82, argv=0xbffe0914) at .././ld/ldmain.c:468
> I had already posted a message about this issue, but it remains without
> answer. I hope this more descriptive version will help.
This is a ld problem. We are paying a high price for some checks that
HJ added to validate linkonce/comdat sections. I approved at least some
of the patches so I share some blame too. HJ has posted some patches to
improve time spent in _bfd_elf_check_kept_section, but they haven't been
applied yet to FSF binutils. I'm not too keen on approving them because
I think they are just bandaids, and the real fix is to revert the symbol
You might like to try compiling HJ's latest release from
ftp.kernel.org/pub/linux/devel/binutils/ which I assume has HJ's
bandaids applied. Please report the link times vs mainline binutils
back here, with and without -g.
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