Re: Bug#164766: Problem with VIA C3 chip and libcrypto
At Mon, 13 Jan 2003 11:36:50 +0000,
David Goodenough wrote:
>
> On Monday 13 January 2003 10:44, Christoph Martin wrote:
> > David Goodenough schrieb:
> > > On Tuesday 05 November 2002 14:27, Daniel Jacobowitz wrote:
> > >>On Tue, Nov 05, 2002 at 02:17:40PM +0000, David Goodenough wrote:
> > >>>On Tuesday 05 November 2002 13:04, Christoph Martin wrote:
> > >>>>Am Die, 2002-11-05 um 01.34 schrieb GOTO Masanori:
> > >>>>>At Mon, 4 Nov 2002 11:07:56 +0100,
> > >>>>>
> > >>>>>Oliver M. Bolzer <oliver@gol.com> wrote:
> > >>>>>>On Mon, Nov 04, 2002 at 09:23:16AM +0000, Ricardo Javier Cardenes
> > >>>>>>Medina <rcardenes@debian.org> wrote...
> > >>>>>>
> > >>>>>>>On Sun, Nov 03, 2002 at 12:13:07PM +0100, Michael Karcher wrote:
> > >>>>>>>>take profit of these instructions, but It seems likely. Is
> > >>>>>>>>there any way to select libraries based on 'instruction set'
> > >>>>>>>>instead of architecture, so the VIA C3 could get code 'without
> > >>>>>>>>cmov', the PII 'with cmov and MMX', the PIII 'with cmov, MMX
> > >>>>>>>>and SSE' and an Athlon processor 'with cmov, MMX and 3D now!',
> > >>>>>>>>although they all are 'family: 6'.
> > >>>>>>>
> > >>>>>>>See at the end of /proc/cpuinfo. The "flags" field. For my Duron:
> > >>>>>>>
> > >>>>>>>flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge
> > >>>>>>>mca cmov pat pse36 mmx fxsr syscall mmxext 3dnowext 3dnow
> > >>>>>>
> > >>>>>>The problem with OpenSSL is, that it is hand-assembly. The author
> > >>>>>>is using the cmov instruction for an i686-optimized routine, though
> > >>>>>>that instruction is not guranteed to be available.
> > >>>>>
> > >>>>>I could not find which source cmov is used, could you tell me?
> > >>>>>If it's the fact, openssl should be fixed in #164766.
> > >>>>
> > >>>>openssl does not use explicitly cmov. On all processors which are
> > >>>>detected as i686 by the linker a library is used which is optimized via
> > >>>>gcc and the -mcpu=i686 flag. This flag brings the cmov in I suspect.
> > >>>>
> > >>>>>>As another C3 user who has to keep libssl on hold for now, I'd
> > >>>>>>suggest that the i686-optimized version be replaced with a version
> > >>>>>>that runs on all i686-family processors.
> > >>>>>>Another option would be to do runtime detection and choose
> > >>>>>>according to that, but that would be without the current
> > >>>>>>convenience that the linker chooses the right lib. As long as the
> > >>>>>>linker only decids on the general processor type, the code for a
> > >>>>>>specific processor type should match the least common denominator.
> > >>>>>
> > >>>>>Yes. It's insane option that linker selects i586 library in only the
> > >>>>>case of "flags: cmov" is detected on VIA C3. It means that linker
> > >>>>>consider "C3 is i586". So, if kernel detects VIA C3, then it's
> > >>>>>natural to be treated with i586 straightforwardly (thus /proc/cpuinfo
> > >>>>>prints processor family: i586).
> > >>>>
> > >>>>This is what I said. The linker (glibc) should fix this.
> > >>>>
> > >>>>Christoph
> > >>>
> > >>>Christoph
> > >>>
> > >>>The linker can not fix this. The C3 is a legitimate 686, it just does
> > >>>not have the OPTIONAL cmov instruction. The kernel therefore correctly
> > >>>shows this as a 686, and the linker tries the i686 directory (I
> > >>> presume). The linker has no way of knowing whether the code in the i686
> > >>> directory uses this optional instruction or not and loads it blindly,
> > >>> hence the problem.
> > >>>
> > >>>I am told (by Alan Cox) that GCC originally uses cmov for 686, before it
> > >>>was realised that it was optional. However looking through google I
> > >>> have not been able to establish when gcc fixed it, and if this fix is
> > >>> present in any 2.9x gcc or only in 3.x. Maybe the maintainer of gcc
> > >>> would know and he may also be able to backfit this fix if it is not in
> > >>> 2.9x
> > >>
> > >>GCC 3.2 still uses CMOVE instructions on -march=i686.
> > >>
> > >>On the other hand:
> > >> {"c3", PROCESSOR_I486, PTA_MMX | PTA_3DNOW},
> > >>GCC disagrees with you that the C3 is an i686.
> > >
> > > Well we have a disagreement between the kernel (which when you specify
> > > C3 actually compiles everything march=i586) which reports in
> > > /proc/cpuinfo that family = 6, and gcc. From all I can find out cmove is
> > > an optional instruction for the 686, and if cmove was not used the code
> > > would run on a C3. So either this is a kernel problem, and the C3 should
> > > be reported as a 586, or it is a gcc problem for generating the wrong
> > > code. Whoever is wrong, the end result is that libssl will not work as
> > > shipped on any machine with a C3 in it - someone needs to fix it.
> > >
> > > I really do not care which package fixes it, as long as it gets fixed.
> > > If we can get agreement on which package should fix it I am happy to see
> > > if I can fix it, and I am quite prepared to test any fix, but I would
> > > rather get agreement as to where the fix should be before I start, as at
> > > the moment everyone is saying it is someone else's fault.
> >
> > Can we please come to a consense who is going to fix this!
> >
> > The VIA C3 is an official i686 and the kernel detects it as this. So it
> > should be legitimate to compile it with -march=i686. But with
> > -march=i686 gcc unconditionally includes CMOV commands which are
> > optional in i686 per specification.
> >
> > So we have three possibilities
> >
> > - gcc stops using CMOV with i686 or includes a flag which turns of CMOV
> > usage.
> > - The kernel detects i686 processors as the C3 which do not support CMOV
> > as i586
> > - The linker detects i686 processors as the C3 which do not support CMOV
> > as i586
> > - libssl drops i686 optimisation and uses i586 for all i686 processors.
> >
> > If the kernel would change it we would have difficulties in specifying
> > the dependencies correctly so that the users get not confused if they
> > use an upstream kernel. So this is deprecated.
> > Changing gcc in one of the ways would only require a Build-Depends on a
> > special gcc version.
> > Changing the linker would require a Depends on a special libc6 for i686.
> >
> > Cheers
> > Christoph
>
> There have been some changes (I believe) in the kernel, at least on
> Alan Cox's version - I am unsure whether it has made the official
> 2.4 tree. It would be worth checking exactly what got changed and
> which official kernel it comes with before making a decision on how
> we close this bug.
Which kernel version do you check? I couldn't find such code...
Resolving in the kernel is very clear for me, without downgrading all
i686 binaries performance...
Regards,
-- gotom
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