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> --- 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; } -- 2.27.0
