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

[Thomas Huth <thuth@redhat.com>]

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

  Thomas