[FFmpeg-devel] [PATCH] swscale: also save ebx register when using PIE

[Michael Niedermayer]

On Mon, Dec 19, 2016 at 11:28:44PM +0100, Andreas Cadhalpun wrote:
> On 16.12.2016 04:08, Michael Niedermayer wrote:
> > On Fri, Dec 16, 2016 at 02:36:53AM +0100, Andreas Cadhalpun wrote:
> >> Otherwise the build fails when configuring with --toolchain=hardened
> >> --disable-pic on i386 using gcc 4.8:
> >> error: PIC register clobbered by '%ebx' in 'asm'
> >>
> >> Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> >> ---
> >>  libswscale/x86/hscale_fast_bilinear_simd.c | 20 ++++++++++----------
> >>  1 file changed, 10 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/libswscale/x86/hscale_fast_bilinear_simd.c b/libswscale/x86/hscale_fast_bilinear_simd.c
> >> index 2cba5f0..3f0f5f5 100644
> >> --- a/libswscale/x86/hscale_fast_bilinear_simd.c
> >> +++ b/libswscale/x86/hscale_fast_bilinear_simd.c
> >> @@ -199,7 +199,7 @@ void ff_hyscale_fast_mmxext(SwsContext *c, int16_t *dst,
> >>  #if ARCH_X86_64
> >>      uint64_t retsave;
> >>  #else
> >> -#if defined(PIC)
> >> +#if defined(PIC) || defined(__PIE__)
> > 
> > please correct me if iam wrong
> > our configure adds -DPIC to define PIC when its enabled,
> > it does not add that in this case but gcc is still generating PIC code
> > that doesnt seem good
> 
> gcc does not generate PIC, only PIE, which is subtly different.

does all the code under PIC work with
PIE that does not have PIC set ?
the identifier seems used a bit in .asm files


> 
> What's wrong here is that this code in swscale tries to determine, whether
> or not the ebx register can be used for asm, but doesn't check that correctly.
> However, configure has a working check for that, the result of which can
> be used here. Patch doing that is attached.

i see your argument for this and it seems sound.
I hope this doesnt break anything as this logic was that way for a
really long time and worked fine and gcc inline asm can be annoying
that said, no objections to the patch 


[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Old school: Use the lowest level language in which you can solve the problem
            conveniently.
New school: Use the highest level language in which the latest supercomputer
            can solve the problem without the user falling asleep waiting.
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