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From: "Jan Beulich" <JBeulich@suse.com>
To: <mingo@elte.hu>, <tglx@linutronix.de>, <hpa@zytor.com>
Cc: <roland@hack.frob.com>, <linux-kernel@vger.kernel.org>,
	<viro@zeniv.linux.org.uk>
Subject: [PATCH] ix86: tighten asmlinkage_protect()
Date: Tue, 22 Jan 2013 11:24:12 +0000	[thread overview]
Message-ID: <50FE84EC02000078000B83B7@nat28.tlf.novell.com> (raw)

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 */
 




             reply	other threads:[~2013-01-22 11:24 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-22 11:24 Jan Beulich [this message]
2013-01-24 20:06 ` [tip:x86/asm] ix86: Tighten asmlinkage_protect() constraints tip-bot for Jan Beulich

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