SIMD vs no SIMD on i686 (was: [Bug 3975] executable stack flag prevents use of libx264.so.148 with selinux in enforcing mode)

[Sérgio Basto]

On Ter, 2016-07-19 at 09:35 +0200, Nicolas Chauvet wrote:
> 2016-07-19 2:55 GMT+02:00  <dominik at greysector.net>:
> > 
> > Hello, Sérgio.
> > 
> > On Tuesday, 19 July 2016 at 02:35, RPM Fusion Bugzilla wrote:
> > > 
> > > https://bugzilla.rpmfusion.org/show_bug.cgi?id=3975
> > > 
> > > --- Comment #4 from Sérgio Basto <sergio at serjux.com> 2016-07-19
> > > 02:35:19 CEST ---
> > > (In reply to comment #3)
> > > > 
> > > > I'll take a look at this. Could you try running execstack -c on
> > > > the installed
> > > > library in the meantime?
> > > Be my guest , in  meantime I read your thread on packaging
> > > Mailing list about
> > > sse3 , I'd like understand if we need 2 builds for i686 ... one
> > > with sse2 other
> > > without it, can you give us your opinion ?
> > The only real concern here are applications linked against libx264,
> > which someone might want to run on low-end hardware, because I
> > don't
> > think anyone would want to encode anything to H.264 on non-SSE2
> > capable
> > CPU (i.e. Pentium 3 or Athlon XP and older). Considering last non-
> > SSE2
> > CPUs went out of production about 8 years ago, I think it's fairly
> > safe
> > to assume that the impact of doing SSE2-only builds would be
> > negligible,
> > if any.
> I'm okay to have a SSE2 only build for single binaries such as pcsx2
> for the following reasons:
> - pcsx2 requires more CPU resources than barely capable sse2 CPU
> anyway.
> - Using sse2 will allow older but sse2 capable CPU to run.
> - Runtime test has to be made to avoid crash and notify user if the
> CPU don't have sse2.
> 
> But for libraries it's not possible to assume a given usage and
> ensure
> users notification.
> I expect you can have webcam app to encode to h264 low profile just
> fine using x264 even on non-sse2 capable cpu.
> It's expected not to crash here.

As I state before, I think, even in this case, x264 asm code, have a
fall back when don't have sse2 instructions and don't crash, that is my
point, but just testing to be sure. I don't see any hardware here to
test it, even though it is a big challenge try install Fedora 24 in
a non-sse2 capable cpu .

> So I don't understand why this discussion raised up again, but I'd
> like not to more anything in i686 that will made some corner case
> users to crash.

Me, Dominik Mierzejewski, Simone Caronni at least have the same
opinion. you should accept the voting ... :) 

Thanks,
-- 
Sérgio M. B.