Commit 4e06fd14 authored by Will Newton's avatar Will Newton Committed by Linus Torvalds

include/linux/unaligned: pack the whole struct rather than just the field

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: default avatarWill Newton <will.newton@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 91facc22
...@@ -3,9 +3,9 @@ ...@@ -3,9 +3,9 @@
#include <linux/kernel.h> #include <linux/kernel.h>
struct __una_u16 { u16 x __attribute__((packed)); }; struct __una_u16 { u16 x; } __attribute__((packed));
struct __una_u32 { u32 x __attribute__((packed)); }; struct __una_u32 { u32 x; } __attribute__((packed));
struct __una_u64 { u64 x __attribute__((packed)); }; struct __una_u64 { u64 x; } __attribute__((packed));
static inline u16 __get_unaligned_cpu16(const void *p) static inline u16 __get_unaligned_cpu16(const void *p)
{ {
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment