Messages in this thread | | | Date | Fri, 27 May 2011 09:38:08 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH] ARM: Do not allow unaligned accesses when CONFIG_ALIGNMENT_TRAP |
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On Thu, May 26, 2011 at 10:51:01PM +0100, Russell King - ARM Linux wrote: > On Thu, May 26, 2011 at 05:03:39PM -0400, Nicolas Pitre wrote: > > It is possible that -fconserve-stack is still valuable on ARM given that > > it is also used with -mno-unaligned-access for other things than > > structure packing on the stack, and therefore its merits can be debated > > independently from the alignment issue at hand. > > Catalin said in his mail "I haven't tried with -mno-unaligned-access, I > suspect the variables on the stack would be aligned.". So I don't think > we know enough to say whether -mno-unaligned-access avoids the stack > packing.
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.
-- Catalin
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