Re: [kvm-unit-tests PATCH] x86: emulator: Fix h_mem usage in tests_smsw

[Paolo Bonzini <pbonzini@redhat.com>]

On 02/12/2014 23:22, Chris J Arges wrote:
> In emulator.c/tests_smsw, smsw (3) fails because h_mem isn't being set correctly
> before smsw is called. By declaring the h_mem function parameter as volatile,
> the compiler no longer optimizes out the assignment before smsw.
> 
> Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
> ---
>  x86/emulator.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/x86/emulator.c b/x86/emulator.c
> index 5aa4dbf..570628f 100644
> --- a/x86/emulator.c
> +++ b/x86/emulator.c
> @@ -337,7 +337,7 @@ void test_incdecnotneg(void *mem)
>      report("lock notb", *mb == vb);
>  }
>  
> -void test_smsw(uint64_t *h_mem)
> +void test_smsw(volatile uint64_t *h_mem)
>  {
>  	char mem[16];
>  	unsigned short msw, msw_orig, *pmsw;
> 

What if you change

        asm volatile("smsw %0" : "=m"(*h_mem));

to

        asm volatile("smsw %0" : "+m"(*h_mem));

Paolo