From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Sat, 16 Aug 2008 07:39:26 +0000 (-0400)
Subject: x86: correct register constraints for 64-bit atomic operations
X-Git-Tag: v2.6.27-rc4~42^2~9
X-Git-Url: http://www.pilppa.org/gitweb/gitweb.cgi?a=commitdiff_plain;h=3c3b5c3b0bf798316a410e27e3d7e6f015663602;p=linux-2.6-omap-h63xx.git

x86: correct register constraints for 64-bit atomic operations

x86_64 add/sub atomic ops does not seems to accept integer values bigger
than 32 bits as immediates. Intel's add/sub documentation specifies they
have to be passed as registers.

The only operations in the x86-64 architecture which accept arbitrary
64-bit immediates is "movq" to any register; similarly, the only
operation which accept arbitrary 64-bit displacement is "movabs" to or
from al/ax/eax/rax.

http://gcc.gnu.org/onlinedocs/gcc-4.3.0/gcc/Machine-Constraints.html

states :

e
    32-bit signed integer constant, or a symbolic reference known to fit
    that range (for immediate operands in sign-extending x86-64
    instructions).
Z
    32-bit unsigned integer constant, or a symbolic reference known to
    fit that range (for immediate operands in zero-extending x86-64
    instructions).

Since add/sub does sign extension, using the "e" constraint seems appropriate.

It applies to 2.6.27-rc, 2.6.26, 2.6.25...

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/include/asm-x86/atomic_64.h b/include/asm-x86/atomic_64.h
index a0095191c02..91c7d03e65b 100644
--- a/include/asm-x86/atomic_64.h
+++ b/include/asm-x86/atomic_64.h
@@ -228,7 +228,7 @@ static inline void atomic64_add(long i, atomic64_t *v)
 {
 	asm volatile(LOCK_PREFIX "addq %1,%0"
 		     : "=m" (v->counter)
-		     : "ir" (i), "m" (v->counter));
+		     : "er" (i), "m" (v->counter));
 }
 
 /**
@@ -242,7 +242,7 @@ static inline void atomic64_sub(long i, atomic64_t *v)
 {
 	asm volatile(LOCK_PREFIX "subq %1,%0"
 		     : "=m" (v->counter)
-		     : "ir" (i), "m" (v->counter));
+		     : "er" (i), "m" (v->counter));
 }
 
 /**
@@ -260,7 +260,7 @@ static inline int atomic64_sub_and_test(long i, atomic64_t *v)
 
 	asm volatile(LOCK_PREFIX "subq %2,%0; sete %1"
 		     : "=m" (v->counter), "=qm" (c)
-		     : "ir" (i), "m" (v->counter) : "memory");
+		     : "er" (i), "m" (v->counter) : "memory");
 	return c;
 }
 
@@ -341,7 +341,7 @@ static inline int atomic64_add_negative(long i, atomic64_t *v)
 
 	asm volatile(LOCK_PREFIX "addq %2,%0; sets %1"
 		     : "=m" (v->counter), "=qm" (c)
-		     : "ir" (i), "m" (v->counter) : "memory");
+		     : "er" (i), "m" (v->counter) : "memory");
 	return c;
 }