The patch titled
include/linux/unaligned: pack the whole struct rather than just the field
has been added to the -mm tree. Its filename is
include-linux-unaligned-pack-the-whole-struct-rather-than-just-the-field.patch
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------------------------------------------------------
Subject: include/linux/unaligned: pack the whole struct rather than just the field
From: Will Newton <will.newton@xxxxxxxxx>
The current packed struct implementation of unaligned access adds the
packed attribute only to the field within the unaligned struct rather than
to the struct as a whole. This is not sufficient to enforce proper
behaviour on architectures with a default struct alignment of more than
one byte.
For example, the current implementation of __get_unaligned_cpu16 when
compiled for arm with gcc -O1 -mstructure-size-boundary=32 assumes the
struct is on a 4 byte boundary so performs the load of the 16bit packed
field as if it were on a 4 byte boundary:
__get_unaligned_cpu16:
ldrh r0, [r0, #0]
bx lr
Moving the packed attribute to the struct rather than the field causes the
proper unaligned access code to be generated:
__get_unaligned_cpu16:
ldrb r3, [r0, #0] @ zero_extendqisi2
ldrb r0, [r0, #1] @ zero_extendqisi2
orr r0, r3, r0, asl #8
bx lr
Signed-off-by: Will Newton <will.newton@xxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/unaligned/packed_struct.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff -puN include/linux/unaligned/packed_struct.h~include-linux-unaligned-pack-the-whole-struct-rather-than-just-the-field include/linux/unaligned/packed_struct.h
--- a/include/linux/unaligned/packed_struct.h~include-linux-unaligned-pack-the-whole-struct-rather-than-just-the-field
+++ a/include/linux/unaligned/packed_struct.h
@@ -3,9 +3,9 @@
#include <linux/kernel.h>
-struct __una_u16 { u16 x __attribute__((packed)); };
-struct __una_u32 { u32 x __attribute__((packed)); };
-struct __una_u64 { u64 x __attribute__((packed)); };
+struct __una_u16 { u16 x; } __attribute__((packed));
+struct __una_u32 { u32 x; } __attribute__((packed));
+struct __una_u64 { u64 x; } __attribute__((packed));
static inline u16 __get_unaligned_cpu16(const void *p)
{
_
Patches currently in -mm which might be from will.newton@xxxxxxxxx are
include-linux-unaligned-pack-the-whole-struct-rather-than-just-the-field.patch
arch-um-drivers-linec-safely-iterate-over-list-of-winch-handlers.patch
include-linux-unaligned-packed_structh-use-__packed.patch
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