linux-kernel - [PATCH 3/4] x86/asm: Add asm macros for static keys/jump labels

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Date:	Fri,  6 Nov 2015 15:12:45 -0800
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 3/4] x86/asm: Add asm macros for static keys/jump labels

Unfortunately, these only work if HAVE_JUMP_LABEL.  In principle, we
could do some serious surgery on the core jump label infrastructure
to keep the patch infrastructure available on x86 on all builds, but
that's probably not worth it.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/include/asm/jump_label.h | 52 +++++++++++++++++++++++++++++++++------
 1 file changed, 44 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index 5daeca3d0f9e..da275c1825f5 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -1,13 +1,6 @@
 #ifndef _ASM_X86_JUMP_LABEL_H
 #define _ASM_X86_JUMP_LABEL_H
 
-#ifndef __ASSEMBLY__
-
-#include <linux/stringify.h>
-#include <linux/types.h>
-#include <asm/nops.h>
-#include <asm/asm.h>
-
 #define JUMP_LABEL_NOP_SIZE 5
 
 #ifdef CONFIG_X86_64
@@ -16,6 +9,14 @@
 # define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC
 #endif
 
+#include <asm/asm.h>
+#include <asm/nops.h>
+
+#ifndef __ASSEMBLY__
+
+#include <linux/stringify.h>
+#include <linux/types.h>
+
 static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
 	asm_volatile_goto("1:"
@@ -59,5 +60,40 @@ struct jump_entry {
 	jump_label_t key;
 };
 
-#endif  /* __ASSEMBLY__ */
+#else	/* __ASSEMBLY__ */
+
+.macro STATIC_JUMP_IF_TRUE target, key, def
+.Lstatic_jump_\@:
+	.if \def
+	/* Equivalent to "jmp.d32 \target" */
+	.byte		0xe9
+	.long		\target - .Lstatic_jump_after_\@
+.Lstatic_jump_after_\@:
+	.else
+	.byte		STATIC_KEY_INIT_NOP
+	.endif
+	.pushsection __jump_table, "aw"
+	_ASM_ALIGN
+	_ASM_PTR	.Lstatic_jump_\@, \target, \key
+	.popsection
+.endm
+
+.macro STATIC_JUMP_IF_FALSE target, key, def
+.Lstatic_jump_\@:
+	.if \def
+	.byte		STATIC_KEY_INIT_NOP
+	.else
+	/* Equivalent to "jmp.d32 \target" */
+	.byte		0xe9
+	.long		\target - .Lstatic_jump_after_\@
+.Lstatic_jump_after_\@:
+	.endif
+	.pushsection __jump_table, "aw"
+	_ASM_ALIGN
+	_ASM_PTR	.Lstatic_jump_\@, \target, \key + 1
+	.popsection
+.endm
+
+#endif	/* __ASSEMBLY__ */
+
 #endif
-- 
2.4.3

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