On Wed, Feb 02, 2011 at 04:24:59PM -0800, Dmitry Torokhov wrote:
On Wed, Feb 02, 2011 at 04:10:04PM -0800, Andreas Schwab wrote:
Dmitry Torokhov <dtor@xxxxxxxxxx> writes:
Even pointers? I'd expect pointers to be aligned on 4-bytes boundaries?
Pointers are not special in any way. Why should they? On the machine
level pointers are just numbers.
Are pointers (along with ints/longs) on m68k naturally aligned on word
boundary even though they are 32 bit?
Anyway, here is the description that introduced alignment statement:
commit 02dba5c6439cff34936460b95cd1ba42b370f345
Author: ak <ak>
Date: Sat Jun 21 16:18:16 2003 +0000
[PATCH] Fix over-alignment problem on x86-64
Thanks to Jan Hubicka who suggested this fix.
The problem seems to be that gcc generates a 32byte alignment for static
objects > 32bytes. This causes gas to set a high alignment on the
section, which causes the uneven (not multiple of sizeof(struct
kernel_param)) section size. The pointer division with a base not being
a multiple of sizeof(*ptr) then causes the invalid result.
This just forces a small alignment, which makes the section end come out
with the correct alignment.
The only mystery left is why ld chose a 16 byte padding instead of
32byte.
BKrev: 3ef485487jZN-h3PtASDeL2Vs55NIg
I guess this does not directly apply to modversions since they are
currently under 32 bytes, but I wonder what happen if we decide to
extend one of the structures involved...
I guess explicitly setting alignment requirement for struct
module_version_attribute is the best option.
So here is the patch that explicitly specifies alignment for struct
module_version_attribute. I tested it on i386 and x86_64 and I believe
it will fix the issue with m68k but I do not have access to such a box.
Thanks,
Dmitry
From f0e0e10b58b22047e36e21a022abf5e86b5819c2 Mon Sep 17 00:00:00 2001
From: Dmitry Torokhov <dtor@xxxxxxxxxx>
Date: Fri, 4 Feb 2011 13:30:10 -0800
Subject: [PATCH] module: explicitly align module_version_attribute structure
We force particular alignment when we generate attribute structures
when generation MODULE_VERSION() data and we need to make sure that
this alignment is followed when we iterate over these structures,
otherwise we may crash on platforms whose natural alignment is not
sizeof(void *), such as m68k.
Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Signed-off-by: Dmitry Torokhov <dtor@xxxxxxxxxx>
---
include/linux/module.h | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/include/linux/module.h b/include/linux/module.h
index e7c6385..de5cd21 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -62,7 +62,7 @@ struct module_version_attribute {
struct module_attribute mattr;
const char *module_name;
const char *version;
-};
+} __attribute__ ((__aligned__(sizeof(void *))));
struct module_kobject
{
--
1.7.3.2
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