Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH] Introduce compat_u64 and compat_s64 types | Date | Sat, 16 Jun 2007 13:21:35 +0200 |
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On Saturday 16 June 2007, Arnd Bergmann wrote: > On Saturday 16 June 2007, David Woodhouse wrote: > > Will GCC know that it needs to emit code to handle that (mis)alignment? > > I've tested this with gcc-4.0.3, and it does the right thing, which > is to split a 4 byte aligned 64 bit load/store into two 32 bit accesses, > if you pass -mstrict-align.
I just realized this was correct but slightly misleading. On powerpc, we don't set the 'attribute((aligned(4)))' on compat_64, so there is never a reason to handle the misalignment, even though it would work.
On x86_64, misaligned loads are always ok, so gcc never needs to care about this, even attribute((packed)) does not cause byte access here.
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