[FFmpeg-devel] [PATCH] fix h264_deblock_sse2.asm segfaults on clang/x86-32

Eli Friedman eli.friedman
Wed Sep 1 08:28:07 CEST 2010

On Tue, Aug 31, 2010 at 11:21 PM, Reimar D?ffinger
<Reimar.Doeffinger at gmx.de> wrote:
> On Wed, Sep 01, 2010 at 02:08:35AM -0400, Alexander Strange wrote:
>> clang on linux/freebsd assumes 4-byte alignment, realigns to 16-byte on entry with attribute_align_arg, but only attempts to retain 4-byte alignment. So any callee code needing an aligned stack and using clang on freebsd/linux needs to realign it themselves.
> My point is about 16-byte aligned stack variables.
> We use those, and with that approach clang can only work either not at all or
> inefficiently with those which is why I am raising the question whether we should
> add possibly slower and more complex code when we maybe won't be able to make all of
> FFmpeg work anyway with that compiler.

By default, clang will automatically realign the stack for functions
which use variables requiring 16 or more bytes of alignment.


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