From 6ebbf2ce437b33022d30badd49dc94d33ecfa498 Mon Sep 17 00:00:00 2001
From: Russell King
Date: Mon, 30 Jun 2014 16:29:12 +0100
Subject: ARM: convert all "mov.* pc, reg" to "bx reg" for ARMv6+

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.

Reported-by: Will Deacon <will.deacon@arm.com>
Tested-by: Stephen Warren <swarren@nvidia.com> # Tegra Jetson TK1
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr> # mioa701_bootresume.S
Tested-by: Andrew Lunn <andrew@lunn.ch> # Kirkwood
Tested-by: Shawn Guo <shawn.guo@freescale.com>
Tested-by: Tony Lindgren <tony@atomide.com> # OMAPs
Tested-by: Gregory CLEMENT <gregory.clement@free-electrons.com> # Armada XP, 375, 385
Acked-by: Sekhar Nori <nsekhar@ti.com> # DaVinci
Acked-by: Christoffer Dall <christoffer.dall@linaro.org> # kvm/hyp
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com> # PXA3xx
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> # Xen
Tested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> # ARMv7M
Tested-by: Simon Horman <horms+renesas@verge.net.au> # Shmobile
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
 arch/arm/xen/hypercall.S | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

(limited to 'arch/arm/xen')

diff --git a/arch/arm/xen/hypercall.S b/arch/arm/xen/hypercall.S
index 44e3a5f10c4c..f00e08075938 100644
--- a/arch/arm/xen/hypercall.S
+++ b/arch/arm/xen/hypercall.S
@@ -58,7 +58,7 @@
 ENTRY(HYPERVISOR_##hypercall)			\
 	mov r12, #__HYPERVISOR_##hypercall;	\
 	__HVC(XEN_IMM);						\
-	mov pc, lr;							\
+	ret lr;					\
 ENDPROC(HYPERVISOR_##hypercall)
 
 #define HYPERCALL0 HYPERCALL_SIMPLE
@@ -74,7 +74,7 @@ ENTRY(HYPERVISOR_##hypercall)			\
 	mov r12, #__HYPERVISOR_##hypercall;	\
 	__HVC(XEN_IMM);						\
 	ldm sp!, {r4}						\
-	mov pc, lr							\
+	ret lr					\
 ENDPROC(HYPERVISOR_##hypercall)
 
                 .text
@@ -101,5 +101,5 @@ ENTRY(privcmd_call)
 	ldr r4, [sp, #4]
 	__HVC(XEN_IMM)
 	ldm sp!, {r4}
-	mov pc, lr
+	ret lr
 ENDPROC(privcmd_call);
-- 
cgit v1.2.3