On Thu, May 6, 2021 at 9:01 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Please use [kvm-unit-tests PATCH ...] for the subject, it took me a depressingly
> long time to figure out which code base this applied to (though admittedly there
> was a non-zero amount of PEBKAC going on).
>
> On Wed, May 05, 2021, Jacob Xu wrote:
> > When compiled with clang, the following statement gets converted into a
> > movaps instructions.
> > mem->u[0] = 5; mem->u[1] = 6; mem->u[2] = 7; mem->u[3] = 8;
> >
> > Since mem is an unaligned pointer to a union of an sse, we get a GP when
> > running.
> >
> > All we want is to make the values between mem and v different for this
> > testcase, so let's just memset the pointer at mem, and convert to
> > uint8_t pointer. Then the compiler will not assume the pointer is
> > aligned to 128 bits.
> >
> > Fixes: e5e76263b5 ("x86: add additional test cases for sse exceptions to
> > emulator.c")
> >
> > Signed-off-by: Jacob Xu <jacobhxu@xxxxxxxxxx>
> > ---
> > x86/emulator.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/x86/emulator.c b/x86/emulator.c
> > index 9705073..672bfda 100644
> > --- a/x86/emulator.c
> > +++ b/x86/emulator.c
> > @@ -716,12 +716,12 @@ static __attribute__((target("sse2"))) void test_sse_exceptions(void *cross_mem)
> >
> > // test unaligned access for movups, movupd and movaps
> > v.u[0] = 1; v.u[1] = 2; v.u[2] = 3; v.u[3] = 4;
> > - mem->u[0] = 5; mem->u[1] = 6; mem->u[2] = 7; mem->u[3] = 8;
> > + memset((uint8_t *)mem, 0, 128);
>
> Shouldn't this be '16', as in 16 bytes / 128 bits? And would it makes sense to
> use a pattern other than '0', if only for giggles?
Or possibly sizeof(*mem)?
