[FFmpeg-devel] Fix Altivec detection on Linux.

Reimar Döffinger Reimar.Doeffinger
Wed Mar 19 19:50:00 CET 2008

On Wed, Mar 19, 2008 at 06:33:20PM +0000, David Woodhouse wrote:
> On Wed, 2008-03-19 at 16:30 +0100, Reimar D?ffinger wrote:
> > On Wed, Mar 19, 2008 at 10:11:09AM -0400, Ronald S. Bultje wrote:
> > > Right now, a ubuntu/ppc package built on a g4 crashes without any notice
> > > whatsoever on a g3, that is unacceptable. There's multiple ways to fix it,
> > > but the unacceptability of any crash should be generally acknowledged.
> > 
> > For Ubuntu the existing but disabled check via mfspr IMO is a very much
> > better solution.
> Why so?

Well, because the code is there and very simple. I am not a fan of
computational libraries like libavcodec doing file-system accesses (even
if to a virtual file system) behind the main application's back.
In addition this is something (contrary to /proc) that any operating
system can implement trivially, though I don't know if the
Debian/FreeBSD kernel combination is something that I just imagine or that
actually exists...

> > Does the proposed patch work on older kernels (e.g. 2.4) or what is its
> > advantage?
> It certainly doesn't crash with SIGILL, like the currently-disabled one.
> On kernels without /proc/$$/auxv it'll silently fall back to assuming no
> Altivec.
> /proc/$$/auxv has been around for a long time, but I don't recall
> offhand whether it was already in 2.4. It was a _long_ time ago that I
> last cared about 2.4 kernels.

Sounds interesting, though I still wished for a really simple, OS-independent
solution to this...

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