[PATCH] ix86: tighten asmlinkage_protect()

[PATCH] ix86: tighten asmlinkage_protect()

[Jan Beulich]

While the description of the commit that originally introduced
asmlinkage_protect() validly says that this doesn't guarantee
clobbering of the function arguments, using "m" constraints rather
than "g" ones reduces the risk (by making it less attractive to the
compiler to move those variables into registers) and generally results
in better code (because we know the arguments are in memory anyway,
and are frequently - if not always - used just once, with the second
[compiler visible] use in asmlinkage_protect() itself being a fake
one).

Signed-off-by: Jan Beulich <jbeulich@suse.com>

---
 arch/x86/include/asm/linkage.h |   18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

--- 3.8-rc4/arch/x86/include/asm/linkage.h
+++ 3.8-rc4-ix86-asmlinkage-protect/arch/x86/include/asm/linkage.h
@@ -27,20 +27,20 @@
 #define __asmlinkage_protect0(ret) \
 	__asmlinkage_protect_n(ret)
 #define __asmlinkage_protect1(ret, arg1) \
-	__asmlinkage_protect_n(ret, "g" (arg1))
+	__asmlinkage_protect_n(ret, "m" (arg1))
 #define __asmlinkage_protect2(ret, arg1, arg2) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2))
 #define __asmlinkage_protect3(ret, arg1, arg2, arg3) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2), "g" (arg3))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3))
 #define __asmlinkage_protect4(ret, arg1, arg2, arg3, arg4) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2), "g" (arg3), \
-			      "g" (arg4))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
+			      "m" (arg4))
 #define __asmlinkage_protect5(ret, arg1, arg2, arg3, arg4, arg5) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2), "g" (arg3), \
-			      "g" (arg4), "g" (arg5))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
+			      "m" (arg4), "m" (arg5))
 #define __asmlinkage_protect6(ret, arg1, arg2, arg3, arg4, arg5, arg6) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2), "g" (arg3), \
-			      "g" (arg4), "g" (arg5), "g" (arg6))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
+			      "m" (arg4), "m" (arg5), "m" (arg6))
 
 #endif /* CONFIG_X86_32 */
 

[tip:x86/asm] ix86: Tighten asmlinkage_protect() constraints

[tip-bot for Jan Beulich]

Commit-ID:  d59fe3f13d070489e63d04e1c9bfd819d5f71542
Gitweb:     http://git.kernel.org/tip/d59fe3f13d070489e63d04e1c9bfd819d5f71542
Author:     Jan Beulich <JBeulich@suse.com>
AuthorDate: Tue, 22 Jan 2013 11:24:12 +0000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 24 Jan 2013 11:25:59 +0100

ix86: Tighten asmlinkage_protect() constraints

While the description of the commit that originally introduced
asmlinkage_protect() validly says that this doesn't guarantee
clobbering of the function arguments, using "m" constraints
rather than "g" ones reduces the risk (by making it less
attractive to the compiler to move those variables into
registers) and generally results in better code (because we know
the arguments are in memory anyway, and are frequently - if not
always - used just once, with the second [compiler visible] use
in asmlinkage_protect() itself being a fake one).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: <roland@hack.frob.com>
Cc: <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/50FE84EC02000078000B83B7@nat28.tlf.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/linkage.h | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index 4814297..79327e9 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -27,20 +27,20 @@
 #define __asmlinkage_protect0(ret) \
 	__asmlinkage_protect_n(ret)
 #define __asmlinkage_protect1(ret, arg1) \
-	__asmlinkage_protect_n(ret, "g" (arg1))
+	__asmlinkage_protect_n(ret, "m" (arg1))
 #define __asmlinkage_protect2(ret, arg1, arg2) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2))
 #define __asmlinkage_protect3(ret, arg1, arg2, arg3) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2), "g" (arg3))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3))
 #define __asmlinkage_protect4(ret, arg1, arg2, arg3, arg4) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2), "g" (arg3), \
-			      "g" (arg4))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
+			      "m" (arg4))
 #define __asmlinkage_protect5(ret, arg1, arg2, arg3, arg4, arg5) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2), "g" (arg3), \
-			      "g" (arg4), "g" (arg5))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
+			      "m" (arg4), "m" (arg5))
 #define __asmlinkage_protect6(ret, arg1, arg2, arg3, arg4, arg5, arg6) \
-	__asmlinkage_protect_n(ret, "g" (arg1), "g" (arg2), "g" (arg3), \
-			      "g" (arg4), "g" (arg5), "g" (arg6))
+	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
+			      "m" (arg4), "m" (arg5), "m" (arg6))
 
 #endif /* CONFIG_X86_32 */