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

[Kevin Hilman <khilman@ti.com>]

Dave Martin <dave.martin@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@linaro.org>
> Tested-by: Jean Pihet <j-pihet@ti.com>

Tested-by: Kevin Hilman <khilman@ti.com>

along with Jean's OMAP patch on:

OMAP2420/n810: including basic suspend/resume test.

OMAP16xx/OSK: boot test only.

Kevin