ARM: 6640/1: Thumb-2: Symbol manipulation macros for function body copying

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 <[email protected]>
Tested-by: Jean Pihet <[email protected]>
Tested-by: Tony Lindgren <[email protected]>
Tested-by: Kevin Hilman <[email protected]>
Signed-off-by: Russell King <[email protected]>

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