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

Michael Niedermayer michaelni
Thu Sep 2 16:42:34 CEST 2010

On Thu, Sep 02, 2010 at 01:28:00PM +0100, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> > On Thu, Sep 02, 2010 at 10:09:20AM +0100, M?ns Rullg?rd wrote:
> >> Michael Niedermayer <michaelni at gmx.at> writes:
> >> 
> >> > On Wed, Sep 01, 2010 at 06:06:11PM +0200, Reimar D?ffinger wrote:
> >> >> On Wed, Sep 01, 2010 at 07:43:29AM -0400, Ronald S. Bultje wrote:
> >> >> > We can optimize the code for compilers that do realign the way we want
> >> >> > if people prefer that.
> >> >> 
> >> >> If there's no measurable slowdown that would just make things worse
> >> >> in the maintainability sense I think.
> >> >> But since the majority does not seem to consider "ignore clang for now"
> >> >> an option I withdraw any objections (well, I mostly meant to ask rather
> >> >> than object anyway).
> >> >
> >> > supporting plain C with clang is all fine but to support clang with
> >> > asm optimizations clang first must support the feature set we require
> >> > for that and maintaining alignment is one of these.
> >> > I dont mind if people disable optimized code for clang or add such
> >> > workarounds conditional on the compiler being clang.
> >> > But iam against such workarounds being added as if it was a bugfix
> >> > because once clang will be fixed all these hacks would then be forgoten
> >> > without ifdef clang/buggy_whatever. And there are enough hacks in the
> >> > code that noone knows why they where added
> >> 
> >> Not aligning the stack is not a bug.
> >
> > is there any relation between your statement and the discussion or what i
> > said?
> You keep talking about workarounds and fixes when the truth is that
> clang is following the published x86 ABI specs, which do not mandate
> an aligned stack.  There is thus nothing to fix per se in clang.  You
> could try submitting a feature request for preserving 16-byte
> alignment since this would be a useful feature.  However, lack of
> something which isn't required can never be considered a bug.

it really makes no difference if its a bug in the compiler or
not and i did not say it is a bug. I spoke about us accumulating crufty
hacks like this that wont ever get found or removed once clang gains
that alignment preserfing feature, that is assuming it doesnt have such
feature optionally already
sorry that i used the word "fix"

and about it being a bug which i really dont see how it matters at all
if clang claims gcc compatibility or defines gcc related version defines
or supports some of the stack realignment function attributes then to
me not keeping stack alignment is a bug


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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