[PATCH] Use correct byte-sized register constraint in __xchg_op()

From: Jeremy Fitzhardinge
Date: Mon Apr 02 2012 - 19:15:59 EST


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@xxxxxxxx>
Reported-by: Leigh Scott <leigh123linux@xxxxxxxxxxxxxx>
Tested-by: Thomas Reitmayr <treitmayr@xxxxxxxxxx>

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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