Messages in this thread | | | Subject | Re: [PATCH] Introduce compat_u64 and compat_s64 types | From | David Woodhouse <> | Date | Sat, 16 Jun 2007 12:34:11 +0100 |
| |
On Sat, 2007-06-16 at 13:21 +0200, Arnd Bergmann wrote: > 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.
You're right. My question was probably not relevant -- all these 64-bit architectures cope with misaligned loads anyway. If we ever have to deal with 32-bit compat on a 64-bit architecture which can't handle misalignment, I'm just going to hide under my desk and never come out.
> 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.
IA64 too, but it'll be handled there too -- either naturally or by fixups; it doesn't matter.
-- dwmw2
- 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/
| |