s390/traps: Fix test_monitor_call() inline assembly

commit 5623bc23a1cb9f9a9470fa73b3a20321dc4c4870 upstream.

The test_monitor_call() inline assembly uses the xgr instruction, which
also modifies the condition code, to clear a register. However the clobber
list of the inline assembly does not specify that the condition code is
modified, which may lead to incorrect code generation.

Use the lhi instruction instead to clear the register without that the
condition code is modified. Furthermore this limits clearing to the lower
32 bits of val, since its type is int.

Fixes: 17248ea03674 ("s390: fix __EMIT_BUG() macro")
Cc: stable@vger.kernel.org
Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c
index 160b2acba8db2b8c51ae542a85b2b0cae4d8be94..908bae8498435152419344ce2a18f1104592bb24 100644 (file)
--- a/arch/s390/kernel/traps.c
+++ b/arch/s390/kernel/traps.c
@@ -284,10 +284,10 @@ static void __init test_monitor_call(void)
                return;
        asm volatile(
                "       mc      0,0\n"
-               "0:     xgr     %0,%0\n"
+               "0:     lhi     %[val],0\n"
                "1:\n"
-               EX_TABLE(0b,1b)
-               : "+d" (val));
+               EX_TABLE(0b, 1b)
+               : [val] "+d" (val));
        if (!val)
                panic("Monitor call doesn't work!\n");
 }