Date: Fri, 9 May 2014 10:12:24 -0700 From: Adrian Chadd <adrian.chadd@gmail.com> To: Dimitry Andric <dim@freebsd.org>, chromium@freebsd.org Cc: Pedro Giffuni <pfg@freebsd.org> Subject: Re: libffmpeg chromium crashes due to unaligned SSE accesses Message-ID: <CAJ-Vmomkzc5LQKLbM%2BoURbBH9Xz=w5i=uaTf3UEjs7wZq-Lc_w@mail.gmail.com> In-Reply-To: <CAJ-VmonLr6m1c-XX-cB-LiQT0JtoGv97dd6VHzYZPCC3hCxreQ@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>
next in thread | previous in thread | raw e-mail | index | archive | help
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 libffmpeg= : >>>>> >>>>> http://www.freebsd.org/cgi/query-pr.cgi?pr=3D189317 >>>>> >>>>> What do you two think? It's that Linux 16 byte alignment on i386 issu= e >>>>> 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 NetBS= D 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 1= 6 >>> 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 SSE >> 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 also >> 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 correct >> 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 version >> 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-Vmomkzc5LQKLbM%2BoURbBH9Xz=w5i=uaTf3UEjs7wZq-Lc_w>