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, 7 insertions, 6 deletions

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 7139d4a7dea7..e52fe5a2d843 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -8,6 +8,7 @@
  * published by the Free Software Foundation.
  */
 
+#include <asm/assembler.h>
 #include <asm/unistd.h>
 #include <asm/ftrace.h>
 #include <asm/unwind.h>
@@ -88,7 +89,7 @@ ENTRY(ret_from_fork)
         cmp     r5, #0
         movne   r0, r4
         adrne   lr, BSYM(1f)
-        movne   pc, r5
+        retne   r5
 1:      get_thread_info tsk
         b       ret_slow_syscall
 ENDPROC(ret_from_fork)
@@ -290,7 +291,7 @@ ENDPROC(ftrace_graph_caller_old)
 
 .macro mcount_exit
         ldmia   sp!, {r0-r3, ip, lr}
-        mov     pc, ip
+        ret     ip
 .endm
 
 ENTRY(__gnu_mcount_nc)
@@ -298,7 +299,7 @@ UNWIND(.fnstart)
 #ifdef CONFIG_DYNAMIC_FTRACE
         mov     ip, lr
         ldmia   sp!, {lr}
-        mov     pc, ip
+        ret     ip
 #else
         __mcount
 #endif
@@ -333,12 +334,12 @@ return_to_handler:
         bl      ftrace_return_to_handler
         mov     lr, r0                  @ r0 has real ret addr
         ldmia   sp!, {r0-r3}
-        mov     pc, lr
+        ret     lr
 #endif
 
 ENTRY(ftrace_stub)
 .Lftrace_stub:
-        mov     pc, lr
+        ret     lr
 ENDPROC(ftrace_stub)
 
 #endif /* CONFIG_FUNCTION_TRACER */
@@ -561,7 +562,7 @@ sys_mmap2:
                 streq   r5, [sp, #4]
                 beq     sys_mmap_pgoff
                 mov     r0, #-EINVAL
-                mov     pc, lr
+                ret     lr
 #else
                 str     r5, [sp, #4]
                 b       sys_mmap_pgoff