Re: Bug#164766: Problem with VIA C3 chip and libcrypto
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.
David
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