[PATCH 5.17 175/298] x86: drop bogus "cc" clobber from __try_cmpxchg_user_asm()

From: Greg Kroah-Hartman
Date: Mon Jun 13 2022 - 10:34:47 EST


From: Jan Beulich <jbeulich@xxxxxxxx>

[ Upstream commit 1df931d95f4dc1c11db1123e85d4e08156e46ef9 ]

As noted (and fixed) a couple of times in the past, "=@cc<cond>" outputs
and clobbering of "cc" don't work well together. The compiler appears to
mean to reject such, but doesn't - in its upstream form - quite manage
to yet for "cc". Furthermore two similar macros don't clobber "cc", and
clobbering "cc" is pointless in asm()-s for x86 anyway - the compiler
always assumes status flags to be clobbered there.

Fixes: 989b5db215a2 ("x86/uaccess: Implement macros for CMPXCHG on user addresses")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Message-Id: <485c0c0b-a3a7-0b7c-5264-7d00c01de032@xxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/x86/include/asm/uaccess.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 1c14bcce88f2..729ecf1e546c 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -466,7 +466,7 @@ do { \
[ptr] "+m" (*_ptr), \
[old] "+a" (__old) \
: [new] ltype (__new) \
- : "memory", "cc"); \
+ : "memory"); \
if (unlikely(__err)) \
goto label; \
if (unlikely(!success)) \
--
2.35.1