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From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@elte.hu>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jason Baron <jbaron@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	"H. Peter Anvin" <hpa@linux.intel.com>
Subject: [PATCH 1/5] x86/jump-label: Use best default nops for inital jump label calls
Date: Fri, 27 Jan 2012 15:14:43 -0500	[thread overview]
Message-ID: <20120127202030.887128048@goodmis.org> (raw)
In-Reply-To: 20120127201442.080360013@goodmis.org

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From: Steven Rostedt <srostedt@redhat.com>

As specified by H. Peter Anvin, the best nops for x86 without knowing
the running computer is:

32bit:
  0x3e, 0x8d, 0x74, 0x26, 0x00

64bit:
  0x0f, 0x1f, 0x44, 0x00, 0x00  also known as P6_NOP5

Currently the default nop that is used by jump label is:

 0xe9 0x00 0x00 0x00 0x00

Which is really a 5byte jump to the next position.

It's better to use a real nop than a jmp.

Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: Jason Baron <jbaron@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 arch/x86/include/asm/jump_label.h |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index a32b18c..cefcfd3 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -3,18 +3,23 @@
 
 #ifdef __KERNEL__
 
+#include <linux/stringify.h>
 #include <linux/types.h>
 #include <asm/nops.h>
 #include <asm/asm.h>
 
 #define JUMP_LABEL_NOP_SIZE 5
 
-#define JUMP_LABEL_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t"
+#ifdef CONFIG_X86_64
+# define JUMP_LABEL_INIT_NOP P6_NOP5
+#else
+# define JUMP_LABEL_INIT_NOP 0x3e, 0x8d, 0x74, 0x26, 0x00
+#endif
 
 static __always_inline bool arch_static_branch(struct jump_label_key *key)
 {
 	asm goto("1:"
-		JUMP_LABEL_INITIAL_NOP
+		".byte " __stringify(JUMP_LABEL_INIT_NOP) "\n\t"
 		".pushsection __jump_table,  \"aw\" \n\t"
 		_ASM_ALIGN "\n\t"
 		_ASM_PTR "1b, %l[l_yes], %c0 \n\t"
-- 
1.7.8.3



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  reply	other threads:[~2012-01-27 20:20 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-27 20:14 [PATCH 0/5] [GIT PULL] x86/jump label: Paranoid checks and 2 or 5 byte nops Steven Rostedt
2012-01-27 20:14 ` Steven Rostedt [this message]
2012-01-27 20:27   ` [PATCH 1/5] x86/jump-label: Use best default nops for inital jump label calls H. Peter Anvin
2012-01-27 20:49     ` Steven Rostedt
2012-01-27 20:50       ` H. Peter Anvin
2012-01-27 21:00         ` Steven Rostedt
2012-01-30 21:05       ` Michal Marek
2012-01-27 20:14 ` [PATCH 2/5] x86/jump-label: Do not bother updating nops if they are correct Steven Rostedt
2012-01-27 20:34   ` Andrew Morton
2012-01-27 20:42     ` Steven Rostedt
2012-01-27 20:14 ` [PATCH 3/5] x86/jump-label: Add safety checks to jump label conversions Steven Rostedt
2012-01-27 20:14 ` [PATCH 4/5] jump labels: Add infrastructure to update jump labels at compile time Steven Rostedt
2012-01-27 20:14 ` [PATCH 5/5] jump labels/x86: Use etiher 5 byte or 2 byte jumps Steven Rostedt
2012-01-27 21:47   ` Steven Rostedt

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