[kvm-unit-tests PATCH 3/4] lib/s390x: Fix the epsw inline assembly

From: Thomas Huth <thuth@redhat.com>
To: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>
Cc: Laurent Vivier <lvivier@redhat.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	David Hildenbrand <david@redhat.com>
Subject: [kvm-unit-tests PATCH 3/4] lib/s390x: Fix the epsw inline assembly
Date: Tue, 22 Jun 2021 15:55:16 +0200	[thread overview]
Message-ID: <20210622135517.234801-4-thuth@redhat.com> (raw)
In-Reply-To: <20210622135517.234801-1-thuth@redhat.com>

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@redhat.com>
---
 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

