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    SubjectRe: [PATCH] ARM: alignment: setup alignment handler earlier
    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

    --
    Catalin
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