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4e06fd14d5
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@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
47 lines
1.1 KiB
C
47 lines
1.1 KiB
C
#ifndef _LINUX_UNALIGNED_PACKED_STRUCT_H
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#define _LINUX_UNALIGNED_PACKED_STRUCT_H
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#include <linux/kernel.h>
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struct __una_u16 { u16 x; } __attribute__((packed));
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struct __una_u32 { u32 x; } __attribute__((packed));
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struct __una_u64 { u64 x; } __attribute__((packed));
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static inline u16 __get_unaligned_cpu16(const void *p)
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{
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const struct __una_u16 *ptr = (const struct __una_u16 *)p;
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return ptr->x;
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}
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static inline u32 __get_unaligned_cpu32(const void *p)
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{
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const struct __una_u32 *ptr = (const struct __una_u32 *)p;
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return ptr->x;
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}
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static inline u64 __get_unaligned_cpu64(const void *p)
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{
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const struct __una_u64 *ptr = (const struct __una_u64 *)p;
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return ptr->x;
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}
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static inline void __put_unaligned_cpu16(u16 val, void *p)
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{
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struct __una_u16 *ptr = (struct __una_u16 *)p;
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ptr->x = val;
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}
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static inline void __put_unaligned_cpu32(u32 val, void *p)
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{
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struct __una_u32 *ptr = (struct __una_u32 *)p;
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ptr->x = val;
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}
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static inline void __put_unaligned_cpu64(u64 val, void *p)
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{
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struct __una_u64 *ptr = (struct __una_u64 *)p;
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ptr->x = val;
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}
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#endif /* _LINUX_UNALIGNED_PACKED_STRUCT_H */
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