Re: Xen 4.18.5 PV dbregs fail

[Manuel Bouyer <bouyer@antioche.eu.org>]

On Mon, May 26, 2025 at 07:06:04PM +0100, Andrew Cooper wrote:
> On 26/05/2025 6:59 pm, Manuel Bouyer wrote:
> > Hello,
> > since I updated to Xen 4.18.5 (from 4.18.4), NetBSD's dbregs-related tests
> > are failing. Only for PV; PVH and HVM guests are fine. They are
> > failing for both 32bits and 64bits guests.
> >
> > I tracked it down to dr6 being 0xffff0ff0 after the trace trap, when at
> > last one of the lower bits should be 1 (I think it's bit 0, from the code).
> >
> > I looked at the commit log between 4.18.4 and 4.18.5 but didn't see
> > anything obvious.
> >
> > Any idea ?
> >
> 
> Have you got a link to the test in question?

For example, dbregs_dr0_trap_code in 
https://cvsweb.netbsd.org/bsdweb.cgi/src/tests/lib/libc/sys/t_ptrace_x86_wait.h?rev=1.33;content-type=text%2Fplain

What's failing is
	ATF_REQUIRE_EQ(info.psi_siginfo.si_code, TRAP_DBREG);

I added printfs in the kernel to show the debug registers when
the process traps, this is where the 0xffff0ff0 value comes from.

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--