Re: [PATCH] KVM: selftests: Fix MWAIT error message when guest assertion fails

[Sean Christopherson <seanjc@google.com>]

On Sun, Nov 19, 2023, Maxim Levitsky wrote:
> On Tue, 2023-11-07 at 10:21 -0800, Sean Christopherson wrote:
> > Print out the test and vector as intended when a guest assert fails an
> > assertion regarding MONITOR/MWAIT faulting.  Unfortunately, the guest
> > printf support doesn't detect such issues at compile-time, so the bug
> > manifests as a confusing error message, e.g. in the most confusing case,
> > the test complains that it got vector "0" instead of expected vector "0".
> > 
> > Fixes: 0f52e4aaa614 ("KVM: selftests: Convert the MONITOR/MWAIT test to use printf guest asserts")
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >  tools/testing/selftests/kvm/x86_64/monitor_mwait_test.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/kvm/x86_64/monitor_mwait_test.c b/tools/testing/selftests/kvm/x86_64/monitor_mwait_test.c
> > index 80aa3d8b18f8..853802641e1e 100644
> > --- a/tools/testing/selftests/kvm/x86_64/monitor_mwait_test.c
> > +++ b/tools/testing/selftests/kvm/x86_64/monitor_mwait_test.c
> > @@ -27,10 +27,12 @@ do {									\
> >  									\
> >  	if (fault_wanted)						\
> >  		__GUEST_ASSERT((vector) == UD_VECTOR,			\
> > -			       "Expected #UD on " insn " for testcase '0x%x', got '0x%x'", vector); \
> > +			       "Expected #UD on " insn " for testcase '0x%x', got '0x%x'", \
> > +			       testcase, vector);			\
> >  	else								\
> >  		__GUEST_ASSERT(!(vector),				\
> > -			       "Expected success on " insn " for testcase '0x%x', got '0x%x'", vector); \
> > +			       "Expected success on " insn " for testcase '0x%x', got '0x%x'", \
> > +			       testcase, vector);			\
> >  } while (0)
> >  
> >  static void guest_monitor_wait(int testcase)
> > 
> > base-commit: 45b890f7689eb0aba454fc5831d2d79763781677
> 
> I think that these days the gcc (and llvm likely) support printf annotations,
> and usually complain, we should look at adding these to have a warning in
> such cases.

Huh.  Well now I feel quite stupid for not realizing that's what

	__attribute__((__format__(printf, ...)))

is for.  There's even a handy dandy __printf() macro now.  I'll post a v2 with
the annotations and fixes for all existing violations.