Date: Fri, 9 May 2014 10:59:40 -0700 From: Adrian Chadd <adrian.chadd@gmail.com> To: Dimitry Andric <dim@freebsd.org>, chromium@freebsd.org, Ed Maste <emaste@freebsd.org> Cc: Pedro Giffuni <pfg@freebsd.org> Subject: Re: libffmpeg chromium crashes due to unaligned SSE accesses Message-ID: <CAJ-VmoniKW39fBJgE1izhizf33ANZPWadsStbV3X6FgrUT1sGQ@mail.gmail.com> In-Reply-To: <CAJ-Vmomkzc5LQKLbM%2BoURbBH9Xz=w5i=uaTf3UEjs7wZq-Lc_w@mail.gmail.com> References: <CAJ-Vmo=C0dEhiK4O9Kunkg-P8ogSC_u_tsf_CQnUZMDvrXR-4g@mail.gmail.com> <536CDD30.40104@FreeBSD.org> <CAJ-Vmo=U3Ow3s728rXiEmfJZY%2BinkQRjiJ0bBvRmf0gALaCeew@mail.gmail.com> <7C272AE1-BA6E-48A9-9662-79B1030D0903@FreeBSD.org> <CAJ-VmonLr6m1c-XX-cB-LiQT0JtoGv97dd6VHzYZPCC3hCxreQ@mail.gmail.com> <CAJ-Vmomkzc5LQKLbM%2BoURbBH9Xz=w5i=uaTf3UEjs7wZq-Lc_w@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
+emaste On 9 May 2014 10:12, Adrian Chadd <adrian.chadd@gmail.com> wrote: > cc'ing chromium@, as this bug is specifically about chrome. > > > -a > > > On 9 May 2014 10:09, Adrian Chadd <adrian.chadd@gmail.com> wrote: >> What's the magic to get the normal ffmpeg port to work right? >> >> >> -a >> >> >> On 9 May 2014 10:05, Dimitry Andric <dim@freebsd.org> wrote: >>> On 09 May 2014, at 18:42, Adrian Chadd <adrian.chadd@gmail.com> wrote: >>>> On 9 May 2014 06:50, Pedro Giffuni <pfg@freebsd.org> wrote: >>>>> Hello; >>>>> >>>>> El 5/9/2014 5:56 AM, Adrian Chadd escribi=C3=B3: >>>>> >>>>>> Hi guys, >>>>>> >>>>>> I filed a PR recently with chromium crashes in its internal libffmpe= g: >>>>>> >>>>>> http://www.freebsd.org/cgi/query-pr.cgi?pr=3D189317 >>>>>> >>>>>> What do you two think? It's that Linux 16 byte alignment on i386 iss= ue >>>>>> that has been creeping up every few years. >>>>>> >>>>> >>>>> Ouch, that's clang, right? >>>> >>>> I gather so? It's whatever the binary package building cluster is >>>> using. I think it's clang for i386. >>> >>> For 10.x and 11.x, that should indeed be clang. >>> >>> >>>> >>>>> I recently brought this from OpenBSD, no idea if it's related: >>>>> >>>>> http://svnweb.freebsd.org/base?view=3Drevision&revision=3D265231 >>>>> >>>>> For now I guess we should just patch the libffmpeg port like the NetB= SD guys >>>>> did. >>>> >>>> Kind of? The x86-64 ABI requires 16 byte alignment for a lot of stuff. >>>> The i386 32 bit ABI doesn't require 16 byte alignment as per >>>> everything pre-Linux-in-2005ish. Linux / gcc flipped the "i386 =3D=3D = 16 >>>> byte alignment now" switch. I vaguely recall that they made >>>> _everything_ 16 byte aligned but I can't be sure. >>> >>> Yes, actually the gcc guys just flipped the switch somewhere in 2008, >>> without any consideration for backwards compatibility, and this lead to >>> quite a bit of wailing, but they WONTFIXed it anyway: >>> >>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D38496 >>> >>> So the problem is that there are quite a lot of projects that simply >>> assume everything on x86 has 16-byte aligned stacks, and you can use SS= E >>> instructions that require strict alignment (e.g. movaps) on any random >>> stack-allocated variable. Obviously, on i386-freebsd, that is not the >>> case, as we still maintain the old SysV 4-byte alignment. >>> >>> FFmpeg is one of those projects that assumes 16-byte alignment, and als= o >>> has a lot of hand-written SSE assembly, either inline or in separate >>> yasm sources. The brute-force way of fixing trouble with alignment is >>> to add -mstackrealign to CFLAGS, but I'm not sure if that is the correc= t >>> solution here. >>> >>> As far as I know, the current FFmpeg port seems to work OK on >>> i386-freebsd, so maybe it could be enough to fix up the Chromium versio= n >>> of FFmpeg in a similar manner as the regular FFmpeg port? I'm not sure >>> I will have enough time to have look at it soon, though... >>> >>> -Dimitry >>>
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAJ-VmoniKW39fBJgE1izhizf33ANZPWadsStbV3X6FgrUT1sGQ>