linux-kernel - [RFC PATCH 1/1] ARM: Ensure correct structure alignment when using compiler attribute "section"

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Date:	Mon, 2 Mar 2015 11:01:42 +0100
From:	Lino Sanfilippo <lsanfil@...vell.com>
To:	<linux@....linux.org.uk>, <linux-arm-kernel@...ts.infradead.org>
CC:	<linux-kernel@...r.kernel.org>, <LinoSanfilippo@....de>,
	Lino Sanfilippo <lsanfil@...vell.com>
Subject: [RFC PATCH 1/1] ARM: Ensure correct structure alignment when using compiler attribute "section"

In some cases structures are placed into dedicated sections by means of the
"section" compiler attribute and then accessed as elements of an array (e.g when
the __clk_of_table is set up which contains all potential clock providers - see
CLK_OF_DECLARE).
But even if the size of such a structure is a multiple of the processors word
size, the linker may decide to use an even greater alignment and thus use
padding in between the structures. In this case accessing a structure as an
array element is not possible. To avoid such padding and thus allow to access
such a structure as an array element enforce an alignment of processor word size
by means of the "aligned" attribute.

Signed-off-by: Lino Sanfilippo <lsanfil@...vell.com>
---
 include/linux/compiler.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 33063f8..6f32128 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -371,7 +371,8 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s

 /* Simple shorthand for a section definition */
 #ifndef __section
-# define __section(S) __attribute__ ((__section__(#S)))
+# define __section(S) __attribute__ ((__section__(#S))) \
+		      __aligned(sizeof(void *))
 #endif

 #ifndef __visible
-- 
1.9.1

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