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>

diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index 48142971b25d095b9724a06a6eff47b2cf302532..79327e9483a34ec33c3ba71bbdc94397f2456f46 100644 (file)
--- 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 */