Bug#842513: vlc: immediate crash on launch on powerpc

[Adrian Bunk]

On Tue, Nov 01, 2016 at 09:56:45AM -0400, Lennart Sorensen wrote:
> On Mon, Oct 31, 2016 at 11:13:00PM +0200, Adrian Bunk wrote:
> > This actually looks like a bug in upstream configure.ac to me:
> >     VLC_ADD_CFLAGS([libvlccore],[${ac_cv_c_altivec}])
> >     ALTIVEC_CFLAGS="$ALTIVEC_FLAGS ${ac_cv_c_altivec} ${ac_cv_c_altivec_abi}"
> >     VLC_ADD_CFLAGS([deinterlace],[${ac_cv_c_altivec} ${ac_cv_c_altivec_abi}])
> > 
> > It is correct that this adds -maltivec to AltiVec-specific code,
> > and vlc has proper autodetection to run this only when AltiVec
> > is actually present.
> > 
> > The VLC_ADD_CFLAGS here look just wrong - it is not the job of 
> > configure.ac to add such flags to generic code (whatever march
> > and hardware features are present is defined through compiler
> > defaults and the CFLAGS passed by the user).
> 
> Actually what looks really wrong is that debian/rules builds ffmpeg with
> --disable-altivec and then builds vlc with --enable-altivec.

This doesn't looks wrong to me.

Note that depending on the software --enable-altivec can either mean
- compile unconditionally for AltiVec, or
- enable AltiVec parts with autodetection to only use them when the
  hardware supports it

> Since powerpc can't assume you have altivec, perhaps vlc shouldn't be
> built with it, or at least ought to have justification for why it is
> done that way.
>...

As I already wrote, vlc contains AltiVec-specific code and autodetection 
for using it only when the hardware supports it.

This should be enabled on all ppc ports, except the SPE one.

--enable-altivec also adding -maltivec elsewhere is a bug.

And due to this bug the whole AltiVec autodetection in vlc is
pretty useless.

> Len Sorensen

cu
Adrian

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