[PATCH v4] ARM: Thumb-2: Symbol manipulation macros for function body copying

Dave Martin dave.martin at linaro.org
Thu Jan 20 04:42:12 EST 2011

On Wed, Jan 19, 2011 at 10:29 PM, Kevin Hilman <khilman at ti.com> wrote:
> Dave Martin <dave.martin at linaro.org> writes:
>> In low-level board support code, there is sometimes a need to
>> copy a function body to another location at run-time.
>> A straightforward call to memcpy doesn't work in Thumb-2,
>> because bit 0 of external Thumb function symbols is set to 1,
>> indicating that the function is Thumb.  Without corrective
>> measures, this will cause an off-by-one copy, and the copy
>> may be called using the wrong instruction set.
>> This patch adds an fncpy() macro to help with such copies.
>> Particular care is needed, because C doesn't guarantee any
>> defined behaviour when casting a function pointer to any other
>> type.  This has been observed to lead to strange optimisation
>> side-effects when doing the arithmetic which is required in
>> order to copy/move function bodies correctly in Thumb-2.
>> Thanks to Russell King and Nicolas Pitre for their input
>> on this patch.
>> Signed-off-by: Dave Martin <dave.martin at linaro.org>
>> Tested-by: Jean Pihet <j-pihet at ti.com>
> Tested-by: Kevin Hilman <khilman at ti.com>
> along with Jean's OMAP patch on:
> OMAP2420/n810: including basic suspend/resume test.
> OMAP16xx/OSK: boot test only.
> Kevin


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