linux-kernel - Immedate Values Optimized Jump Fix

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Message-ID: <20080717025738.GA23277@Krystal>
Date:	Wed, 16 Jul 2008 22:57:38 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	ltt-dev@...ts.casi.polymtl.ca, linux-kernel@...r.kernel.org,
	Takashi Nishiie <t-nishiie@...css.fujitsu.com>
Subject: Immedate Values Optimized Jump Fix

I rarely emit a single patch for a fix wrt LTTng (I usually just release
a new version), but this one is worth it. It will be in 0.11 pretty
soon, but if you want to apply it to 0.10 meanwhile, it's highly
recommended.

Caused a kernel OOPS when loading the tracepoint probes once in a while
on a 8-way x86_64.


Immedate Values Optimized Jump Fix

Fix the immediate values optimized jump fallback, which parameters were wrong
following the last changes. It should be a 5 bytes instruction (not 2) with a 4
bytes operand.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
---
 arch/x86/kernel/immediate.c |    2 +-
 include/asm-x86/immediate.h |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6-lttng/arch/x86/kernel/immediate.c
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/immediate.c	2008-07-16 22:50:35.000000000 -0400
+++ linux-2.6-lttng/arch/x86/kernel/immediate.c	2008-07-16 22:51:07.000000000 -0400
@@ -500,7 +500,7 @@ __kprobes int arch_imv_update(struct __i
 				"Jump target fallback at %lX, nr fail %d\n",
 				imv->imv, ++nr_fail);
 #endif
-			imv->size = 1;
+			imv->size = 4;	/* Fallback on movl */
 		} else {
 #ifdef DEBUG_IMMEDIATE
 			static int nr_success;
Index: linux-2.6-lttng/include/asm-x86/immediate.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-x86/immediate.h	2008-07-16 22:49:19.000000000 -0400
+++ linux-2.6-lttng/include/asm-x86/immediate.h	2008-07-16 22:51:07.000000000 -0400
@@ -132,7 +132,7 @@ struct __imv {
 		BUILD_BUG_ON(sizeof(__typeof__(name##__imv)) > 1);	\
 		asm (".section __imv,\"aw\",@progbits\n\t"		\
 			_ASM_PTR "%c1, (3f)-4\n\t"			\
-			".byte 0, 2\n\t"				\
+			".byte 0, 5\n\t"				\
 			".previous\n\t"					\
 			"mov $0,%0\n\t"					\
 			"3:\n\t"					\

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