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 <rmk+ker...@arm.linux.org.uk>
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-König <u.kleine-koe...@pengutronix.de>
but I wonder what is the reason to not use bx if \reg != lr.
Thanks
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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