linux-kernel - [PATCH 5.4 87/87] x86: drop bogus "cc" clobber from __try_cmpxchg_user

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Date:   Wed, 27 Jul 2022 18:11:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jan Beulich <jbeulich@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.4 87/87] x86: drop bogus "cc" clobber from __try_cmpxchg_user_asm()

From: Jan Beulich <jbeulich@...e.com>

commit 1df931d95f4dc1c11db1123e85d4e08156e46ef9 upstream.

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@...e.com>
Message-Id: <485c0c0b-a3a7-0b7c-5264-7d00c01de032@...e.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/include/asm/uaccess.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -498,7 +498,7 @@ __pu_label:							\
 		       [ptr] "+m" (*_ptr),				\
 		       [old] "+a" (__old)				\
 		     : [new] ltype (__new)				\
-		     : "memory", "cc");					\
+		     : "memory");					\
 	if (unlikely(__err))						\
 		goto label;						\
 	if (unlikely(!success))						\