Messages in this thread | | | Date | Wed, 7 Sep 2011 18:24:45 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH] ARM: alignment: setup alignment handler earlier |
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On Wed, Sep 07, 2011 at 06:04:52PM +0100, Russell King - ARM Linux wrote: > On Wed, Sep 07, 2011 at 05:42:19PM +0100, Måns Rullgård wrote: > > There are such instructions (ldrd, ldm), but gcc will not emit those > > unless the address is known to be aligned. For ARMv6 and later, gcc 4.6 > > *will* emit potentially unaligned ldr and ldrh since these very clearly > > allow an unaligned address and are faster than the alternatives in all > > implementations to date. This is unless strict alignment checking is > > explicitly enabled, which unfortunately the Linux kernel does for no > > apparent reason at all. > > "no apparant reason at all" heh. The reason is to keep the code > simple and free from bugs. To do otherwise means that each of the > CPU files needs to be littered with ifdefs to deal with the alignment > fault configuration, of which there are 16 of them (ignoring v6 and v7.) > > If you think code maintanence of the same thing in 16 places is efficient > then I guess there is "no apparant reason". I beg to differ, being one > of those folk who have had to edit 18 different places several times. > > So no, I do not intend to move this: > > #ifdef CONFIG_ALIGNMENT_TRAP > orr r0, r0, #CR_A > #else > bic r0, r0, #CR_A > #endif > > into 16 separate places in the kernel.
What about something like this (untested):
#if defined(CONFIG_ALIGNMENT_TRAP) && __LINUX_ARM_ARCH__ < 6 orr r0, r0, #CR_A #else bic r0, r0, #CR_A #endif
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