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    SubjectRe: [PATCH] ARM: alignment: setup alignment handler earlier
    On 7 September 2011 17:28, Russell King - ARM Linux
    <> wrote:
    > On Wed, Sep 07, 2011 at 03:40:16PM +0100, Catalin Marinas wrote:
    >> On Wed, Sep 07, 2011 at 02:35:04PM +0100, John Ogness wrote:
    >> > From 6f3f381800367127dc6430d9b9fa9bd6fc6d8ed0 Mon Sep 17 00:00:00 2001
    >> > From: John Ogness <>
    >> >
    >> > The alignment exception handler is setup fairly late in
    >> > the boot process (fs_initcall). However, with newer gcc
    >> > versions and the compiler option -fconserve-stack, code
    >> > accessing unaligned data is generated in functions that
    >> > are called earlier, for example pcpu_dump_alloc_info().
    >> > This results in unhandled alignment exceptions during
    >> > boot. By setting up the exception handler sooner, we
    >> > reduce the window where a compiler may generate code
    >> > accessing unaligned data.
    >> While this reduces the window and fixes this particular case, it still
    >> doesn't solve the problem. We never know when some unaligned access
    >> would be generated for some earlier code.
    > Is the problem even solvable?  There are instructions on ARMv6+ which
    > always produce an alignment fault (eg, ldrd) irrespective of strict
    > alignment checking.

    We can just hope that the compiler isn't that bad as to generate
    unaligned accesses with those instructions that are known to fault.
    That's what I would consider a compiler bug.

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      Last update: 2011-09-07 18:45    [W:0.020 / U:43.728 seconds]
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