On Wed, 1 Dec 2010 22:11:53 +0000 Will Newton <[email protected]> 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 <[email protected]> > --- > 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)); > Yes, that was wrong. Do you think this bug affects 2.6.36 or earlier? Even if it doesn't, it looks like a bit of a hand-grenade to leave it unfixed in earlier kernels. _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
