Re: Bug#1037264: cksum crashes intermittently with "Illegal instruction" on some Xen DomU

[Pádraig Brady]

On 13/06/2023 09:38, Axel Beckert wrote:
> Hi, especially to Pádraig,

> Pádraig Brady wrote:
> > cksum since v9.0 checks at runtime whether pclmul is supported.
> > It seems that check is not working appropriately on a Xen DomU.
> > The routine in question is pclmul_supported() at:
> > https://github.com/coreutils/coreutils/blob/b841f111/src/cksum.c#L160-L191
> >
> > That either suggests xen is incorrectly setting PCLMUL and AVX bits,
> > or perhaps these two bits are not sufficient.
> > Hmm I wonder do we also need to explicitly check for SSSE3 support?
> >
> > I.e. I wonder does cksum built with the following help?
> […]
> > diff --git a/src/cksum.c b/src/cksum.c
> > index 85afab0ac..98733dadf 100644
> > --- a/src/cksum.c
> > +++ b/src/cksum.c
> > @@ -172,7 +172,7 @@ pclmul_supported (void)
> >         return false;
> >       }
> >
> > -  if (! (ecx & bit_PCLMUL) || ! (ecx & bit_AVX))
> > +  if (! (ecx & bit_PCLMUL) || ! (ecx & bit_AVX) || ! (ecx & bit_SSSE3))
> >       {
> >         if (cksum_debug)
> >           error (0, 0, "%s", _("pclmul support not detected"));
>
> No, the patch unfortunately didn't help:

It's great you can test changes at least.
Thanks for trying the above.

At this stage it would be good to get the output from `cpuid -1`
so that hopefully we can get something there to key on
that indicates the cpu doesn't support the instructions.

thanks,
Pádraig