[PATCH] ARM: convert all "mov.* pc, reg" to "bx reg" for ARMv6+

On Tue, Jul 01, 2014 at 04:58:24PM +0100, Russell King wrote:

ARMv6 and greater introduced a new instruction ("bx") which can be used
to return from function calls.  Recent CPUs perform better when the
"bx lr" instruction is used rather than the "mov pc, lr" instruction,
and this sequence is strongly recommended to be used by the ARM
architecture manual (section A.4.1.1).

We provide a new macro "ret" with all its variants for the condition
code which will resolve to the appropriate instruction.

Rather than doing this piecemeal, and miss some instances, change all
the "mov pc" instances to use the new macro, with the exception of
the "movs" instruction and the kprobes code.  This allows us to detect
the "mov pc, lr" case and fix it up - and also gives us the possibility
of deploying this for other registers depending on the CPU selection.

Signed-off-by: Russell King <redacted>

Works fine on my ARM-v7M machine:

$ objdump -d vmlinux | grep -E 'mov.*pc'
8c000022:	46e7      	mov	pc, ip
8c000028:	46ef      	mov	pc, sp
8c000b26:	46af      	movne	pc, r5
8c0037e0:	4687      	mov	pc, r0
8c0828d2:	4697      	mov	pc, r2
8c1213ee:	469f      	mov	pc, r3

Also boots fine.

Tested-by: Uwe Kleine-K?nig <redacted>

but I wonder what is the reason to not use bx if \reg != lr.

Thanks
Uwe

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Pengutronix e.K.                           | Uwe Kleine-K?nig            |
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