Date: Tue, 13 Sep 2016 16:43:04 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: incompatibility between libtheora/mmx and musl ? On Tue, Sep 13, 2016 at 08:06:49PM +0200, u-uy74@...ey.se wrote: > Hello, > > Libtheora contains an assembler part for ia32 and x86_64 which has been > in use for many years, with at least both glibc and uclibc. > > Now, musl-based builds of libtheora for ia32 with this code enabled > lead to the encoder segfaulting. No problem when using the C version. > > This is seen when building at Aetey. Ffmpeg in Alpine exhibits the same > problem, too (strictly speaking, possibly another problem but ffmpeg > crashes there with the same pattern, when encoding to theora). > > People at Xiph do not have any musl-based system and want really detailed > debugging info which implies tracing through musl and following malloc's > internal data (which is what seems to become corrupted). > > In other words, the detailed knowledge (xiph and musl) is located > separately from each other and also from the motivation (aetey, alpine > and possibly others). > > I would appreciate some help and suggestions. The alternative is diving > into mmx-assembler and musl code or resorting to C-only routines which > give roughly half of the performance of the assembler ones. > > More details are there at > > https://trac.xiph.org/ticket/2287 > > There is also a corresponding > > https://bugs.alpinelinux.org/issues/6132 The most likely explanation is that they're overflowing a heap buffer. Perhaps it would be possible to pad all their malloc/realloc calls with +64 or so to see if that makes the problem go away. If so that gives a good starting point for tracking down the bug. Rich
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