On Fri, Sep 24, 2021 at 12:51:47AM +0000, Oliver Upton wrote:
> Compiling the KVM selftests with clang emits the following warning:
>
> >> include/x86_64/processor.h:297:25: error: variable 'xmm0' is uninitialized when used here [-Werror,-Wuninitialized]
> >> return (unsigned long)xmm0;
>
> where xmm0 is accessed via an uninitialized register variable.
>
> Indeed, this is a misuse of register variables, which really should only
> be used for specifying register constraints on variables passed to
> inline assembly. Rather than attempting to read xmm registers via
> register variables, just explicitly perform the movq from the desired
> xmm register.
>
> Fixes: 783e9e51266e ("kvm: selftests: add API testing infrastructure")
> Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
> ---
> .../selftests/kvm/include/x86_64/processor.h | 34 +++++++++----------
> 1 file changed, 17 insertions(+), 17 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
> index 242ae8e09a65..eba8bd08293e 100644
> --- a/tools/testing/selftests/kvm/include/x86_64/processor.h
> +++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
> @@ -312,37 +312,37 @@ static inline void set_xmm(int n, unsigned long val)
> }
> }
>
> -typedef unsigned long v1di __attribute__ ((vector_size (8)));
> +#define GET_XMM(__xmm) \
> +({ \
> + unsigned long __val; \
> + asm volatile("movq %%"#__xmm", %0" : "=r"(__val) : : #__xmm); \
> + __val; \
> +})
> +
> static inline unsigned long get_xmm(int n)
> {
> assert(n >= 0 && n <= 7);
>
> - register v1di xmm0 __asm__("%xmm0");
> - register v1di xmm1 __asm__("%xmm1");
> - register v1di xmm2 __asm__("%xmm2");
> - register v1di xmm3 __asm__("%xmm3");
> - register v1di xmm4 __asm__("%xmm4");
> - register v1di xmm5 __asm__("%xmm5");
> - register v1di xmm6 __asm__("%xmm6");
> - register v1di xmm7 __asm__("%xmm7");
> switch (n) {
> case 0:
> - return (unsigned long)xmm0;
> + return GET_XMM(xmm0);
> case 1:
> - return (unsigned long)xmm1;
> + return GET_XMM(xmm1);
> case 2:
> - return (unsigned long)xmm2;
> + return GET_XMM(xmm2);
> case 3:
> - return (unsigned long)xmm3;
> + return GET_XMM(xmm3);
> case 4:
> - return (unsigned long)xmm4;
> + return GET_XMM(xmm4);
> case 5:
> - return (unsigned long)xmm5;
> + return GET_XMM(xmm5);
> case 6:
> - return (unsigned long)xmm6;
> + return GET_XMM(xmm6);
> case 7:
> - return (unsigned long)xmm7;
> + return GET_XMM(xmm7);
> }
> +
> + /* never reached */
> return 0;
> }
>
> --
> 2.33.0.685.g46640cef36-goog
>
Reviewed-by: Ricardo Koller <ricarkol@xxxxxxxxxx>
