On Tue, 22 Jun 2021 15:55:16 +0200 Thomas Huth <thuth@xxxxxxxxxx> wrote: > According to the Principles of Operation, the epsw instruction > does not touch the second register if it is r0. With GCC we were > lucky so far that it never tried to use r0 here, but when compiling > the kvm-unit-tests with Clang, this indeed happens and leads to > very weird crashes. Thus let's make sure to never use r0 for the > second operand of the epsw instruction. > > Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx> Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> maybe also mention in the patch description why you changed + to = > --- > lib/s390x/asm/arch_def.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h > index 3aa5da9..15cf7d4 100644 > --- a/lib/s390x/asm/arch_def.h > +++ b/lib/s390x/asm/arch_def.h > @@ -265,7 +265,7 @@ static inline uint64_t extract_psw_mask(void) > > asm volatile( > " epsw %0,%1\n" > - : "+r" (mask_upper), "+r" (mask_lower) : : ); > + : "=r" (mask_upper), "=a" (mask_lower)); > > return (uint64_t) mask_upper << 32 | mask_lower; > }
