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, 4 insertions, 4 deletions

diff --git a/arch/arm/nwfpe/entry.S b/arch/arm/nwfpe/entry.S
index d18dde95b8aa..5d65be1f1e8a 100644
--- a/arch/arm/nwfpe/entry.S
+++ b/arch/arm/nwfpe/entry.S
@@ -19,7 +19,7 @@
     along with this program; if not, write to the Free Software
     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
-
+#include <asm/assembler.h>
 #include <asm/opcodes.h>
 
 /* This is the kernel's entry point into the floating point emulator.
@@ -92,7 +92,7 @@ emulate:
         mov     r0, r6                  @ prepare for EmulateAll()
         bl      EmulateAll              @ emulate the instruction
         cmp     r0, #0                  @ was emulation successful
-        moveq   pc, r4                  @ no, return failure
+        reteq   r4                      @ no, return failure
 
 next:
 .Lx1:   ldrt    r6, [r5], #4            @ get the next instruction and
@@ -102,7 +102,7 @@ next:
         teq     r2, #0x0C000000
         teqne   r2, #0x0D000000
         teqne   r2, #0x0E000000
-        movne   pc, r9                  @ return ok if not a fp insn
+        retne   r9                      @ return ok if not a fp insn
 
         str     r5, [sp, #S_PC]         @ update PC copy in regs
 
@@ -115,7 +115,7 @@ next:
         @ plain LDR instruction.  Weird, but it seems harmless.
         .pushsection .fixup,"ax"
         .align  2
-.Lfix:  mov     pc, r9                  @ let the user eat segfaults
+.Lfix:  ret     r9                      @ let the user eat segfaults
         .popsection
 
         .pushsection __ex_table,"a"