Messages in this thread | | | Date | Sat, 18 Dec 2010 12:59:23 +0000 | Subject | Re: [PATCH] include/linux/unaligned: Pack the whole struct rather than just the field. | From | Will Newton <> |
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On Tue, Dec 7, 2010 at 11:12 AM, Will Newton <will.newton@gmail.com> wrote: > On Wed, Dec 1, 2010 at 10:11 PM, Will Newton <will.newton@gmail.com> wrote: >> 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> > > I don't know of any designated maintainer for this code, but add a > couple of ccs of people who might be interested. > > This change doesn't change any behaviour on current architectures, but > is more correct and may enable other architectures to move to the > packed struct unaligned access implementation and so allow us to move > more architectures to the asm-generic implementation.
Ping!
Does anyone have any opinions on this?
>> --- >> include/linux/unaligned/packed_struct.h | 6 +++--- >> 1 files changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/include/linux/unaligned/packed_struct.h >> b/include/linux/unaligned/packed_struct.h >> index 2498bb9..c9a6abd 100644 >> --- a/include/linux/unaligned/packed_struct.h >> +++ b/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) >> { >> -- >> 1.7.0.4 >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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