[PATCH] ARM: Do not allow unaligned accesses when CONFIG_ALIGNMENT_TRAP

On Fri, May 27, 2011 at 09:38:08AM +0100, Catalin Marinas wrote:

OK, I tried this now:

-fconserve-stack: we get unaligned accesses on the stack because the
newer versions of gcc turned unaligned accesses on by default.

-fconserve-stack -mno-unaligned-access: the stack variables are aligned.
We probably get the benefit of -fconserve-stack as well.

So as per the initial post in this thread, we could have
-mno-unaligned-access on ARM always on (when CONFIG_ALIGNMENT_TRAP). As
Nicolas suggested, we could compile some files with -munaligned-access
(and maybe -fno-conserve-stack).

I raised this with the gcc guys so they are looking into it. But it
really doesn't look like a gcc bug as long as -mno-unaligned-access is
taken into account.

Ok, we need to check one last thing, and that's what the behaviour is
with -mno-unaligned-access and packed structures (such as the ethernet
header).  If it makes no difference, then I suggest we always build
with -mno-unaligned-access.