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Re: sse{2,3,4.2}, altivec, neon, ...




On Sat, Aug 05, 2017 at 10:04:28PM +0200, Philipp Kern wrote:
> On 08/05/2017 07:53 PM, Adam Borowski wrote:
> > Thus, here's a proposed solution: in unstable, there's now a bunch of
> > packages that do such checking in preinst, and thus refuse (overridably) to
> > even install such software.
> > 
> > Currently this includes:
> > * sse2: i386 (inc. hurd-i386, kfreebsd-i386)
> > * sse3: i386, amd64, x32 (〃, kfreebsd-amd64)
> > * sse4.2: i386, amd64, x32 (〃)
> > * neon: armhf
> > * altivec: powerpc
> 
> I suppose it wouldn't be possible to add autodetection to debhelper or
> at least lintian based on instructions present in the binary? For the
> latter I'd imagine something with a low certainty suggesting that you
> depend on a certain meta package. (To catch the cases where there's
> actually autodetection at runtime.)

It's easy to quite reliably detect the presence of such instructions
(probably no one JITs such code).  There's no real way to check if it's
executed unconditionally, though -- a lot of software has optimized code
paths that are chosen at runtime.

I guess we could apply such check to the archive: for example, if any of
these instructions are present in a code section:

orpd cvtdq2ps andpd cmpnltpd addpd psubq cmpeqsd cvtpd2dq punpcklqdq pshuflw
cvttpd2dq paddq cvttps2dq cmpneqpd cmpordpd cvtpd2ps cmpneqsd xorpd pmuludq
cmplesd subpd cvtpd2pi pshufhw cvttsd2si psrldq movupd movmskpd cmpunordsd
cmpnltsd movq2dq maskmovdqu cvtsi2sd cmppd cvttpd2pi sqrtsd movnti cmpltsd
comisd minpd ucomisd cmpnlepd minsd maxsd mfence pshufd unpckhpd cmplepd
punpckhqdq divsd mulpd cmpltpd cmpunordpd maxpd lfence shufpd subsd movhpd
mulsd cvtps2pd unpcklpd movntdq movapd cvtsd2ss movdqu andnpd cvtps2dq
movdqa cvtsd2si cmpordsd movdq2q divpd sqrtpd cvtpi2pd movntpd pslldq
cvtss2sd cmpeqpd cmpnlesd movlpd addsd cvtdq2pd

then the program may need sse2.  But there's no good way to weed out false
positives automatically, so all we'd get is a list of candidates to check.


Meow!
-- 
⢀⣴⠾⠻⢶⣦⠀ What Would Jesus Do, MUD/MMORPG edition:
⣾⠁⢰⠒⠀⣿⡁ • multiplay with an admin char to benefit your mortal
⢿⡄⠘⠷⠚⠋⠀ • abuse item cloning bugs (the five fishes + two breads affair)
⠈⠳⣄⠀⠀⠀⠀ • use glitches to walk on water