Re: Bug#887327: gcc-7: missed optimization of glibc strspn SSE 4.2 variant
control: tag -1 + fixed-upstream
On 2018-01-15 00:22, Aurelien Jarno wrote:
> clone 887169 -1
> reassign -1 gcc-7
> retitle -1 gcc-7: missed optimization of glibc strspn SSE 4.2 variant
> forwarded -1 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81481
> block 887169 by -1
> thanks
>
> On 2018-01-14 10:35, James Lu wrote:
> > Package: libc6
> > Version: 2.26-3
> > Severity: normal
> >
> > Dear maintainers,
> >
> > On a recent glibc upgrade on buster/sid (first to 2.26-2 and then
> > 2.26-3), one Steam game (Civilization V) consistently segfaults on startup.
> >
> > Similar issues have been reported in Arch Linux[1], Fedora[2], and
> > OpenSUSE[3], where the consensus was that building glibc with
>
> From what I get about the above reported issues, this bug is caused by:
> - the Steam games not following the Linux/x86 ABI wrt stack alignement
> - the SSE4.2 version of the strspn function needing to push an SSE
> register to the stack when build with GCC 7, due to a missed
> optimization.
>
> > -mstackrealign fixed the issue. (I haven't been able to get such a local
> > build working though)
>
> I don't think it is actually the consensus, only Arch Linux has chosen
> this solution, and building the whole glibc with this option will have
> an impact of the performances for all binaries, not only the broken
> Steam ones. I therefore don't think it's the right way to fix the bug.
>
> Instead it looks like fixing PR81481 [1] on the GCC 7 side, and then
> rebuilding glibc is the way to go. I am therefore cloning this bug to
> gcc-7 so that it can happens.
Note that the bug has now been fixed upstream. Tagging this bug as such.
Aurelien
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Aurelien Jarno GPG: 4096R/1DDD8C9B
aurelien@aurel32.net http://www.aurel32.net
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