linux-kernel - [PATCH] Use correct byte-sized register constraint in __xchg

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Date:	Mon, 02 Apr 2012 16:15:33 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	the arch/x86 maintainers <x86@...nel.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Reitmayr <treitmayr@...base.at>,
	leigh123linux@...glemail.com, Dave Jones <davej@...hat.com>
Subject: [PATCH] Use correct byte-sized register constraint in __xchg_op()

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>
Reported-by: Leigh Scott <leigh123linux@...glemail.com>
Tested-by: Thomas Reitmayr <treitmayr@...base.at>

diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
index b3b7332..bc18d0e 100644
--- 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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