Re: intel_iommu unit test is also failing (was: Re: [PATCH kvm-unit-tests] realmode: load above stack)

[Peter Xu <peterx@redhat.com>]

On Mon, May 04, 2026 at 10:07:25AM +0200, Thomas Huth wrote:
> On 04/05/2026 09.58, Thomas Huth wrote:
> > On 04/06/2024 16.35, Paolo Bonzini wrote:
> > > The bottom 32K of memory are generally reserved for use by the BIOS;
> > > for example, traditionally the boot loader is placed at 0x7C00 and
> > > the stack grows below that address.
> > > 
> > > It turns out that with some versions of clang, realmode.flat has
> > > become big enough that it overlaps the stack used by the multiboot
> > > option ROM loader.  The result is that a couple instructions are
> > > overwritten.  Typically one or two tests fail and that's it...
> > > 
> > > Move the code above the forbidden region, in real 90s style.
> > > 
> > > Reported-by: Thomas Huth <thuth@redhat.com>
> > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > > ---
> > >   x86/realmode.lds | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/x86/realmode.lds b/x86/realmode.lds
> > > index 0ed3063b..e4782a98 100644
> > > --- a/x86/realmode.lds
> > > +++ b/x86/realmode.lds
> > > @@ -1,6 +1,6 @@
> > >   SECTIONS
> > >   {
> > > -    . = 16K;
> > > +    . = 32K;
> > >       stext = .;
> > >       .text : { *(.init) *(.text) }
> > >       . = ALIGN(4K);
> > 
> >   Hi Paolo!
> > 
> > FYI, the realmode kvm-unit-test now also fails with the recent version
> > of GCC 16 for the i386 target:
> > 
> >   https://gitlab.com/kvm-unit-tests/kvm-unit-tests/-/jobs/14195195727
> > 
> > It was working fine some weeks ago with GCC 15.1:
> > 
> >   https://gitlab.com/kvm-unit-tests/kvm-unit-tests/-/jobs/13977260961
> > 
> > When I apply your patch, the problem seems to be gone again in this
> > case, but since there were some other issues with this (with older
> > versions of GCC, I think):
> > 
> > https://lore.kernel.org/kvm/49f8aadf-6e3f-4d2b-a32a-8ba941a3a2a1@redhat.com/
> > 
> > ... there must be a better way to fix it?
> > 
> > Could you please have a look?
> 
> By the way, the intel_iommu test now also suddenly started failing (for the
> x86_64 target), either due to update of GCC or due to the update from QEMU
> v10.2 to 11.0 :
> 
>  https://gitlab.com/kvm-unit-tests/kvm-unit-tests/-/jobs/14195195728
> 
> Two weeks ago, it was still working fine:
> 
>  https://gitlab.com/kvm-unit-tests/kvm-unit-tests/-/jobs/13977260962

Looping in those who take care of qemu's VT-D now (Yi, Clément)..

-- 
Peter Xu