[PATCH 01/13] ARM: add fncpy.h from linux v4.6

[Sascha Hauer]

On Thu, Jan 21, 2021 at 12:29:46PM +0100, Steffen Trumtrar wrote:
> From: Steffen Trumtrar <s.trumtrar at pengutronix.de>
> 
> Description from the linux commit 5756e9dd0de6d5c307773f8f734c0684b3098fdd:
> 
>     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: Steffen Trumtrar <s.trumtrar at pengutronix.de>
> ---
>  arch/arm/include/asm/fncpy.h | 82 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 82 insertions(+)
>  create mode 100644 arch/arm/include/asm/fncpy.h

Applied this patch for now, but with an update to v5.10 with the only
change that the licence header is changed to SPDX now.

Sascha


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