[Ffmpeg-devel] about ff_check_alignment()

[Måns Rullgård]

"Mario Rossi" <mariofutire at googlemail.com> writes:

> On Tue Jan 30 13:30:52 CET 2007, Uoti Urpala wrote:
>
>> On Tue, 2007-01-30 at 09:00 +0100, Guillaume POIRIER wrote:
>> > On 1/30/07, yubing <trueice at gmail.com> wrote:
>> >
>> > > I wonder which compiler the developers are using, would you refer an
>> > > appropriate compiler to me?
>> >
>> > gcc 4.2 or 4.3
>
>> You don't need a development branch compiler for proper stack variable
>> alignment. GCC 4.1 works. I don't currently have GCC 4.0 (or older)
>> installed, it might or might not work.
>
> I have the same warning (about stack not aligned), but only when
> running xine (1.1.4).
> I'm compiling everything with GCC 4.1.1 (shipped with Fedora Core 5).
>
> Xine contains a copy of ffmpeg which is compiled within xine compilation.
> What I've found, is that xine passes this switch to the compiler
>
> -mpreferred-stack-boundary=2
>
> when compiling ffmpeg.
>
> On a small test with a standalone ff_check_alignment(), this switch is
> enough to cause the test to fail. The default is =4 (i.e. 16 bytes).
>
> Should I write to xine mailing list?

Yes.  They are explicitly breaking ffmpeg.

> What happens when the stack is not aligned as ffmpeg expects it to be?

It might crash.

-- 
M?ns Rullg?rd
mans at mansr.com