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

[Nicolas Chauvet]

2016-07-19 13:36 GMT+02:00 Sérgio Basto <sergio at serjux.com>:
> 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 .

You could setup a x86 32bit virtual machine using KVM install fedora,
then mask cpu, or use pentium 3 as a CPU for the guest vm and reboot.

If the x264 works (not only not crash) then there is no reason not to
enable asm by default there.


-- 
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Nicolas (kwizart)