linux-kernel - [ 40/75] x86: Use correct byte-sized register constraint in __xchg

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Message-Id: <20120419210306.541037055@linuxfoundation.org>
Date:	Thu, 19 Apr 2012 14:03:43 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Jeremy Fitzhardinge <jeremy@...p.org>,
	Leigh Scott <leigh123linux@...glemail.com>,
	Thomas Reitmayr <treitmayr@...base.at>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [ 40/75] x86: Use correct byte-sized register constraint in
 __xchg_op()

3.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeremy Fitzhardinge <jeremy@...p.org>

commit 2ca052a3710fac208eee690faefdeb8bbd4586a1 upstream.

x86-64 can access the low half of any register, but i386 can only do
it with a subset of registers.  'r' causes compilation failures on i386,
but 'q' expresses the constraint properly.

Signed-off-by: Jeremy Fitzhardinge <jeremy@...p.org>
Link: http://lkml.kernel.org/r/4F7A3315.501@goop.org
Reported-by: Leigh Scott <leigh123linux@...glemail.com>
Tested-by: Thomas Reitmayr <treitmayr@...base.at>
Signed-off-by: H. Peter Anvin <hpa@...or.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/include/asm/cmpxchg.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/cmpxchg.h
+++ b/arch/x86/include/asm/cmpxchg.h
@@ -43,7 +43,7 @@ extern void __add_wrong_size(void)
 		switch (sizeof(*(ptr))) {				\
 		case __X86_CASE_B:					\
 			asm volatile (lock #op "b %b0, %1\n"		\
-				      : "+r" (__ret), "+m" (*(ptr))	\
+				      : "+q" (__ret), "+m" (*(ptr))	\
 				      : : "memory", "cc");		\
 			break;						\
 		case __X86_CASE_W:					\


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