linux-kernel - [PATCH] Linux Kernel Markers

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Date:	Tue, 2 Oct 2007 08:10:08 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	akpm@...ux-foundation.org
Cc:	Christoph Hellwig <hch@...radead.org>,
	Mike Mason <mmlnx@...ibm.com>,
	"Frank Ch. Eigler" <fche@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] Linux Kernel Markers - Alignment Fix

Linux Kernel Markers - Alignment Fix

Fix the alignment of the struct marker declaration in the trace_mark() macro.
Otherwise, we run into problems on 64 bits architectures where the struct marker
structure is bigger than 32 bytes : gcc becomes alignment-happy and align these
structures on 32 bytes while the iteration on the markers is itself only aligned
on 8 bytes, as specified by the type attribute. Specifying the alignmentof the
type only is not enough to restrain gcc happiness; we must specify a variable
alignment attribute too.

This bug causes NULL pointer dereference at module load time on x86_64
when we load marker-example.ko.

Thanks to Mike Mason for reporting this.

It applies to 2.6.23-rc8-mm2, after the linux kernel markers coding style
fixes. This is an important bugfix that should be merged with the
markers.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC: Christoph Hellwig <hch@...radead.org>
CC: Mike Mason <mmlnx@...ibm.com>
CC: "Frank Ch. Eigler" <fche@...hat.com>
---
 include/linux/marker.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6-lttng/include/linux/marker.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/marker.h	2007-10-02 07:33:21.000000000 -0400
+++ linux-2.6-lttng/include/linux/marker.h	2007-10-02 07:33:58.000000000 -0400
@@ -58,7 +58,7 @@ struct marker {
 		__attribute__((section("__markers_strings")))		\
 		= format;						\
 		static struct marker __mark_##name			\
-		__attribute__((section("__markers"))) =			\
+		__attribute__((section("__markers"), aligned(8))) =	\
 		{ __mstrtab_name_##name, __mstrtab_format_##name,	\
 		0, __mark_empty_function, NULL };			\
 		asm volatile ("" : : "i" (&__mark_##name));		\
-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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