linux-kernel - Re: [GIT PULL] x86: cleanup alternative.h (v3)

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Date:	Tue, 28 Apr 2009 14:13:40 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [GIT PULL] x86: cleanup alternative.h (v3)

Alternative header duplicates assembly that could be merged in one single macro.
Merging this into this macro also allows to directly declare ALTERNATIVE()
statements within assembly code.

Uses a __stringify() of the feature bits rather than passing a "i" operand.
Leave the old %0 operand as-is (set to 0), unused to stay compatible with API.

Update :
align comments, align code.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC: 'Ingo Molnar' <mingo@...e.hu>
CC: H. Peter Anvin <hpa@...or.com>
CC: Andi Kleen <andi@...stfloor.org>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/include/asm/alternative.h |   59 ++++++++++++++-----------------------
 1 file changed, 23 insertions(+), 36 deletions(-)

Index: linux-2.6-lttng/arch/x86/include/asm/alternative.h
===================================================================
--- linux-2.6-lttng.orig/arch/x86/include/asm/alternative.h	2009-04-28 13:47:03.000000000 -0400
+++ linux-2.6-lttng/arch/x86/include/asm/alternative.h	2009-04-28 13:48:38.000000000 -0400
@@ -3,6 +3,7 @@
 
 #include <linux/types.h>
 #include <linux/stddef.h>
+#include <linux/stringify.h>
 #include <asm/asm.h>
 
 /*
@@ -74,6 +75,22 @@ static inline void alternatives_smp_swit
 
 const unsigned char *const *find_nop_table(void);
 
+/* alternative assembly primitive */
+#define ALTERNATIVE(oldinstr, newinstr, feature) 			\
+									\
+      "661:\n\t" oldinstr "\n662:\n"					\
+      ".section .altinstructions,\"a\"\n"				\
+      _ASM_ALIGN "\n"							\
+      _ASM_PTR "661b\n"				/* label */		\
+      _ASM_PTR "663f\n"				/* new instruction */	\
+      ".byte " __stringify(feature) "\n"	/* feature bit */	\
+      ".byte 662b-661b\n"			/* sourcelen */		\
+      ".byte 664f-663f\n"			/* replacementlen */	\
+      ".previous\n"							\
+      ".section .altinstr_replacement,\"ax\"\n"				\
+      "663:\n\t" newinstr "\n664:\n"		/* replacement */	\
+      ".previous"
+
 /*
  * Alternative instructions for different CPU types or capabilities.
  *
@@ -87,18 +104,7 @@ const unsigned char *const *find_nop_tab
  * without volatile and memory clobber.
  */
 #define alternative(oldinstr, newinstr, feature)			\
-	asm volatile ("661:\n\t" oldinstr "\n662:\n"			\
-		      ".section .altinstructions,\"a\"\n"		\
-		      _ASM_ALIGN "\n"					\
-		      _ASM_PTR "661b\n"		/* label */		\
-		      _ASM_PTR "663f\n"		/* new instruction */	\
-		      "	 .byte %c0\n"		/* feature bit */	\
-		      "	 .byte 662b-661b\n"	/* sourcelen */		\
-		      "	 .byte 664f-663f\n"	/* replacementlen */	\
-		      ".previous\n"					\
-		      ".section .altinstr_replacement,\"ax\"\n"		\
-		      "663:\n\t" newinstr "\n664:\n"  /* replacement */	\
-		      ".previous" :: "i" (feature) : "memory")
+	asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 
 /*
  * Alternative inline assembly with input.
@@ -109,35 +115,16 @@ const unsigned char *const *find_nop_tab
  * Best is to use constraints that are fixed size (like (%1) ... "r")
  * If you use variable sized constraints like "m" or "g" in the
  * replacement make sure to pad to the worst case length.
+ * Leaving an unused argument 0 to keep API compatibility.
  */
 #define alternative_input(oldinstr, newinstr, feature, input...)	\
-	asm volatile ("661:\n\t" oldinstr "\n662:\n"			\
-		      ".section .altinstructions,\"a\"\n"		\
-		      _ASM_ALIGN "\n"					\
-		      _ASM_PTR "661b\n"		/* label */		\
-		      _ASM_PTR "663f\n"		/* new instruction */	\
-		      "	 .byte %c0\n"		/* feature bit */	\
-		      "	 .byte 662b-661b\n"	/* sourcelen */		\
-		      "	 .byte 664f-663f\n"	/* replacementlen */	\
-		      ".previous\n"					\
-		      ".section .altinstr_replacement,\"ax\"\n"		\
-		      "663:\n\t" newinstr "\n664:\n"  /* replacement */	\
-		      ".previous" :: "i" (feature), ##input)
+	asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)		\
+		: : "i" (0), ## input)
 
 /* Like alternative_input, but with a single output argument */
 #define alternative_io(oldinstr, newinstr, feature, output, input...)	\
-	asm volatile ("661:\n\t" oldinstr "\n662:\n"			\
-		      ".section .altinstructions,\"a\"\n"		\
-		      _ASM_ALIGN "\n"					\
-		      _ASM_PTR "661b\n"		/* label */		\
-		      _ASM_PTR "663f\n"		/* new instruction */	\
-		      "	 .byte %c[feat]\n"	/* feature bit */	\
-		      "	 .byte 662b-661b\n"	/* sourcelen */		\
-		      "	 .byte 664f-663f\n"	/* replacementlen */	\
-		      ".previous\n"					\
-		      ".section .altinstr_replacement,\"ax\"\n"		\
-		      "663:\n\t" newinstr "\n664:\n"  /* replacement */ \
-		      ".previous" : output : [feat] "i" (feature), ##input)
+	asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)		\
+		: output : "i" (0), ## input)
 
 /*
  * use this macro(s) if you need more than one output parameter

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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