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>

2 files changed, 15 insertions, 15 deletions

diff --git a/arch/arm/vfp/entry.S b/arch/arm/vfp/entry.S
index fe6ca57..2e78760 100644
--- a/arch/arm/vfp/entry.S
+++ b/arch/arm/vfp/entry.S
@@ -34,7 +34,7 @@ ENDPROC(do_vfp)
 
 ENTRY(vfp_null_entry)
 	dec_preempt_count_ti r10, r4
-	mov	pc, lr
+	ret	lr
 ENDPROC(vfp_null_entry)
 
 	.align	2
@@ -49,7 +49,7 @@ ENTRY(vfp_testing_entry)
 	dec_preempt_count_ti r10, r4
 	ldr	r0, VFP_arch_address
 	str	r0, [r0]		@ set to non-zero value
-	mov	pc, r9			@ we have handled the fault
+	ret	r9			@ we have handled the fault
 ENDPROC(vfp_testing_entry)
 
 	.align	2
diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index be807625..cda654c 100644
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S
@@ -183,7 +183,7 @@ vfp_hw_state_valid:
 					@ always subtract 4 from the following
 					@ instruction address.
 	dec_preempt_count_ti r10, r4
-	mov	pc, r9			@ we think we have handled things
+	ret	r9			@ we think we have handled things
 
 
 look_for_VFP_exceptions:
@@ -202,7 +202,7 @@ look_for_VFP_exceptions:
 
 	DBGSTR	"not VFP"
 	dec_preempt_count_ti r10, r4
-	mov	pc, lr
+	ret	lr
 
 process_exception:
 	DBGSTR	"bounce"
@@ -234,7 +234,7 @@ ENTRY(vfp_save_state)
 	VFPFMRX	r12, FPINST2		@ FPINST2 if needed (and present)
 1:
 	stmia	r0, {r1, r2, r3, r12}	@ save FPEXC, FPSCR, FPINST, FPINST2
-	mov	pc, lr
+	ret	lr
 ENDPROC(vfp_save_state)
 
 	.align
@@ -245,7 +245,7 @@ vfp_current_hw_state_address:
 #ifdef CONFIG_THUMB2_KERNEL
 	adr	\tmp, 1f
 	add	\tmp, \tmp, \base, lsl \shift
-	mov	pc, \tmp
+	ret	\tmp
 #else
 	add	pc, pc, \base, lsl \shift
 	mov	r0, r0
@@ -257,10 +257,10 @@ ENTRY(vfp_get_float)
 	tbl_branch r0, r3, #3
 	.irp	dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
 1:	mrc	p10, 0, r0, c\dr, c0, 0	@ fmrs	r0, s0
-	mov	pc, lr
+	ret	lr
 	.org	1b + 8
 1:	mrc	p10, 0, r0, c\dr, c0, 4	@ fmrs	r0, s1
-	mov	pc, lr
+	ret	lr
 	.org	1b + 8
 	.endr
 ENDPROC(vfp_get_float)
@@ -269,10 +269,10 @@ ENTRY(vfp_put_float)
 	tbl_branch r1, r3, #3
 	.irp	dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
 1:	mcr	p10, 0, r0, c\dr, c0, 0	@ fmsr	r0, s0
-	mov	pc, lr
+	ret	lr
 	.org	1b + 8
 1:	mcr	p10, 0, r0, c\dr, c0, 4	@ fmsr	r0, s1
-	mov	pc, lr
+	ret	lr
 	.org	1b + 8
 	.endr
 ENDPROC(vfp_put_float)
@@ -281,14 +281,14 @@ ENTRY(vfp_get_double)
 	tbl_branch r0, r3, #3
 	.irp	dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
 1:	fmrrd	r0, r1, d\dr
-	mov	pc, lr
+	ret	lr
 	.org	1b + 8
 	.endr
 #ifdef CONFIG_VFPv3
 	@ d16 - d31 registers
 	.irp	dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
 1:	mrrc	p11, 3, r0, r1, c\dr	@ fmrrd	r0, r1, d\dr
-	mov	pc, lr
+	ret	lr
 	.org	1b + 8
 	.endr
 #endif
@@ -296,21 +296,21 @@ ENTRY(vfp_get_double)
 	@ virtual register 16 (or 32 if VFPv3) for compare with zero
 	mov	r0, #0
 	mov	r1, #0
-	mov	pc, lr
+	ret	lr
 ENDPROC(vfp_get_double)
 
 ENTRY(vfp_put_double)
 	tbl_branch r2, r3, #3
 	.irp	dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
 1:	fmdrr	d\dr, r0, r1
-	mov	pc, lr
+	ret	lr
 	.org	1b + 8
 	.endr
 #ifdef CONFIG_VFPv3
 	@ d16 - d31 registers
 	.irp	dr,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
 1:	mcrr	p11, 3, r0, r1, c\dr	@ fmdrr	r0, r1, d\dr
-	mov	pc, lr
+	ret	lr
 	.org	1b + 8
 	.endr
 #endif