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, 2016-07-26 at 16:54 +0100, Sérgio Basto wrote:
> On Ter, 2016-07-26 at 14:28 +0200, Nicolas Chauvet wrote:
> > 
> > 2016-07-25 4:36 GMT+02:00 Sérgio Basto <sergio at serjux.com>:
> > > 
> > > 
> > > On Seg, 2016-07-25 at 04:02 +0200, Kevin Kofler wrote:
> > > > 
> > > > 
> > > > So for those stuck with such an old machine, it
> > > > is better to have a library that works (slowly) than one that
> > > > just
> > > > crashes
> > > > with a SIGILL (illegal instruction).
> > > I think x264 , detects if have the cpu instructions and if not,
> > > have
> > > one fall back code, don't crash.
> > Okay to put an end to this thread, here are the tests:
> > 
> > # x264 -o out.mp4  BigBuckBunny_320x180.mp4
> > lavf [info]: 320x180p 1:1 @ 24/1 fps (vfr)
> > x264 [error]: your cpu does not support SSE1, but x264 was compiled
> > with asm
> > x264 [error]: to run x264, recompile without asm (configure --
> > disable-asm)
> > x264 [error]: x264_encoder_open failed
> > # mv /usr/lib/libx264.so.148 /usr/lib/sse2/
> > # mv /tmp/libx264.so.148 /usr/lib/
> > # ldconfig
> > # x264 -o out.mp4  BigBuckBunny_320x180.mp4
> > lavf [info]: 320x180p 1:1 @ 24/1 fps (vfr)
> > x264 [info]: using SAR=1/1
> > x264 [info]: using cpu capabilities: none!
> > x264 [info]: profile High, level 1.2
> > x264 [info]: frame I:5     Avg QP:17.11  size: 13610
> > 
> > This was tested on KVM guest with pentium 2 cpu emulated. Here are
> > the
> > relevant cpuinfo flags there:
> > flags        : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> > mca cmov pat pse36 mmx fxsr eagerfpu x2apic hypervisor vmmcall
> > (no mmx, or sse1/2 here).
> > 
> > Actually, I've tested on pentium3 which has sse1 but not sse2 and
> > the
> > asm version worked there, so the runtime cpu detection work
> > starting
> > with sse1, but not sse2.
> > 
> > The last cpuinfo case which is relevant to the thread is either
> > this
> > work on AMD geode (probably one of the last produced 32bit only x86
> > cpu)
> > As seen here the result might be random:
> > http://wiki.laptop.org/go/Geode_instruction_set#supported_SSE1, but
> > sse is unlikely to be advertised by cpuinfo
> > This last is specially relevant for the OLPC project.
> > 
> > 
> > At the end, I think it's urgent not to move anything already
> > working
> > fine in legacy architecture.
> yeah , so at least doesn't crash and I was right about x264 have
> fallback code for pentium3 (so the runtime cpu detection work
> starting
> with sse1), which makes me think because of pentium2 we don't have
> full
> features ... , but OK, for now, makes sense disable asm on i686 ...
> BTW and for 10b ? (compile with --bit-depth=10 ) make sense also make
> 2
> builds or can I enable asm there ? or just leave as is (one build
> without asm).  
> 
> I also read yesterday, about http://emmabuntus.sourceforge.net/, This
> distribution was originally designed to facilitate the reconditioning
> of computers, given to humanitarian organizations ... 
> 

Thinking betterm since doesn't crash , and in pentium 2 we have a
message to disable-asm , I think we should enable asm by default , and
at most drop a note in wiki , that PII are not supported or something
like that . 


> > 
> > Thx
> > 
> > 
-- 
Sérgio M. B.