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>

1 files changed, 5 insertions, 5 deletions

diff --git a/arch/arm/kernel/debug.S b/arch/arm/kernel/debug.S
index 14f7c3b14632..78c91b5f97d4 100644
--- a/arch/arm/kernel/debug.S
+++ b/arch/arm/kernel/debug.S
@@ -90,7 +90,7 @@ ENTRY(printascii)
                 ldrneb  r1, [r0], #1
                 teqne   r1, #0
                 bne     1b
-                mov     pc, lr
+                ret     lr
 ENDPROC(printascii)
 
 ENTRY(printch)
@@ -105,7 +105,7 @@ ENTRY(debug_ll_addr)
                 addruart r2, r3, ip
                 str     r2, [r0]
                 str     r3, [r1]
-                mov     pc, lr
+                ret     lr
 ENDPROC(debug_ll_addr)
 #endif
 
@@ -116,7 +116,7 @@ ENTRY(printascii)
                 mov     r0, #0x04               @ SYS_WRITE0
         ARM(    svc     #0x123456       )
         THUMB(  svc     #0xab           )
-                mov     pc, lr
+                ret     lr
 ENDPROC(printascii)
 
 ENTRY(printch)
@@ -125,14 +125,14 @@ ENTRY(printch)
                 mov     r0, #0x03               @ SYS_WRITEC
         ARM(    svc     #0x123456       )
         THUMB(  svc     #0xab           )
-                mov     pc, lr
+                ret     lr
 ENDPROC(printch)
 
 ENTRY(debug_ll_addr)
                 mov     r2, #0
                 str     r2, [r0]
                 str     r2, [r1]
-                mov     pc, lr
+                ret     lr
 ENDPROC(debug_ll_addr)
 
 #endif