Date: Fri, 9 May 2014 23:49:11 +0200 From: Dimitry Andric <dim@FreeBSD.org> To: Adrian Chadd <adrian.chadd@gmail.com> Cc: chromium@freebsd.org, Pedro Giffuni <pfg@freebsd.org> Subject: Re: libffmpeg chromium crashes due to unaligned SSE accesses Message-ID: <FC7C93ED-F20B-4999-BF84-280F9DA9926A@FreeBSD.org> In-Reply-To: <CAJ-VmoknOe8d9H5o8D1XMWn%2Bq%2B_aJ-B46URwkOsnVkWAXEhamw@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> <9810619D-DF65-4A4F-9720-B22DC791EA65@FreeBSD.org> <CAJ-VmoknOe8d9H5o8D1XMWn%2Bq%2B_aJ-B46URwkOsnVkWAXEhamw@mail.gmail.com>
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[-- Attachment #1 --] I think you are referring to the --enable-memalign-hack option passed to ffmpeg's configure script? That is something related to posix_memalign(), not to stack alignment. That said, I just built the chromium port with its default options, and while I cannot get it to crash, I cannot get it to display any video either. It must be because I'm running a VMware guest, and chromium does not cope with that too well (Firefox seems to work much better, though not terribly fast). What kind of activity should make chromium crash? Just running it, or displaying a certain website? -Dimitry On 09 May 2014, at 21:11, Adrian Chadd <adrian.chadd@gmail.com> wrote: > There's an alignment hack option in the ffmpeg port though. It's not a > cflags thing, it's a ./configure thing. > > > > > -a > > > On 9 May 2014 11:40, Dimitry Andric <dim@freebsd.org> wrote: >> I just tried building multimedia/ffmpeg on i386-freebsd11, with the default port settings, and it seems to work just fine. I tried transcoding a few files, and there were no stack alignment problems or SIGBUSes. >> >> Looking at the build logs, I see >> >> C compiler cc >> ARCH x86 (generic) >> big-endian no >> runtime cpu detection yes >> yasm yes >> MMX enabled yes >> MMXEXT enabled yes >> 3DNow! enabled yes >> 3DNow! extended enabled yes >> SSE enabled yes >> SSSE3 enabled yes >> AVX enabled yes >> FMA4 enabled yes >> i686 features enabled yes >> CMOV is fast no >> EBX available yes >> EBP available yes >> ... >> >> The command line flags used for compilation (wrapped for clarity) don't seem to include specific ones that change stack alignment behavior: >> >> cc \ >> -I. \ >> -I./ \ >> -DLIBICONV_PLUG \ >> -D_ISOC99_SOURCE \ >> -D_FILE_OFFSET_BITS=64 \ >> -D_LARGEFILE_SOURCE \ >> -DHAVE_AV_CONFIG_H \ >> -O2 \ >> -pipe \ >> -march=corei7 \ >> -DLIBICONV_PLUG \ >> -fno-strict-aliasing \ >> -msse \ >> -I/usr/local/include/vorbis \ >> -I/usr/local/include \ >> -std=c99 \ >> -fomit-frame-pointer \ >> -I/usr/local/include \ >> -I/usr/local/include/freetype2 \ >> -I/usr/local/include/libpng15 \ >> -I/usr/local/include \ >> -I/usr/local/include/p11-kit-1 \ >> -I/usr/local/include/freetype2 \ >> -I/usr/local/include/libpng15 \ >> -I/usr/local/include/opencv \ >> -I/usr/local/include \ >> -I/usr/local/include/schroedinger-1.0 \ >> -I/usr/local/include/orc-0.4 \ >> -Wdeclaration-after-statement \ >> -Wall \ >> -Wno-parentheses \ >> -Wno-switch \ >> -Wno-format-zero-length \ >> -Wdisabled-optimization \ >> -Wpointer-arith \ >> -Wredundant-decls \ >> -Wno-pointer-sign \ >> -Wwrite-strings \ >> -Wtype-limits \ >> -Wundef \ >> -Wmissing-prototypes \ >> -Wno-pointer-to-int-cast \ >> -Wstrict-prototypes \ >> -O3 \ >> -fno-math-errno \ >> -fno-signed-zeros \ >> -Qunused-arguments \ >> -Werror=implicit-function-declaration \ >> -Werror=missing-prototypes \ >> -Werror=return-type \ >> -MMD \ >> -c \ >> >> I'll build chromium with the default options, and see what happens. >> >> -Dimitry >> >> On 09 May 2014, at 19:09, 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 escribió: >>>>>> >>>>>>> Hi guys, >>>>>>> >>>>>>> I filed a PR recently with chromium crashes in its internal libffmpeg: >>>>>>> >>>>>>> http://www.freebsd.org/cgi/query-pr.cgi?pr=189317 >>>>>>> >>>>>>> What do you two think? It's that Linux 16 byte alignment on i386 issue >>>>>>> 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=revision&revision=265231 >>>>>> >>>>>> For now I guess we should just patch the libffmpeg port like the NetBSD 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 == 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=38496 >>>> >>>> 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 >>>> >> [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.22 (Darwin) iEYEARECAAYFAlNtTWAACgkQsF6jCi4glqNDtACfapbhi/IH62nkJWHQhxebX84x Fn0AoIpbUfsrDmYgk8PzE1ndkn/yLpTu =HOTG -----END PGP SIGNATURE-----help
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