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/crypto/aes-armv4.S

@@ -35,6 +35,7 @@
 @ that is being targetted.
 
 #include <linux/linkage.h>
+#include <asm/assembler.h>
 
 .text
 
@@ -648,7 +649,7 @@ _armv4_AES_set_encrypt_key:
 
 .Ldone:	mov	r0,#0
 	ldmia   sp!,{r4-r12,lr}
-.Labrt:	mov	pc,lr
+.Labrt:	ret	lr
 ENDPROC(private_AES_set_encrypt_key)
 
 .align	5

arch/arm/include/asm/assembler.h

@@ -427,4 +427,25 @@ THUMB(	orr	\reg , \reg , #PSR_T_BIT	)
 #endif
 	.endm
 
+	.irp	c,,eq,ne,cs,cc,mi,pl,vs,vc,hi,ls,ge,lt,gt,le,hs,lo
+	.macro	ret\c, reg
+#if __LINUX_ARM_ARCH__ < 6
+	mov\c	pc, \reg
+#else
+	.ifeqs	"\reg", "lr"
+	bx\c	\reg
+	.else
+	mov\c	pc, \reg
+	.endif
+#endif
+	.endm
+	.endr
+
+	.macro	ret.w, reg
+	ret	\reg
+#ifdef CONFIG_THUMB2_KERNEL
+	nop
+#endif
+	.endm
+
 #endif /* __ASM_ASSEMBLER_H__ */

arch/arm/include/asm/entry-macro-multi.S

@@ -35,5 +35,5 @@
 \symbol_name:
 	mov	r8, lr
 	arch_irq_handler_default
-	mov     pc, r8
+	ret	r8
 	.endm

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

arch/arm/kernel/entry-armv.S

@@ -224,7 +224,7 @@ svc_preempt:
 1:	bl	preempt_schedule_irq		@ irq en/disable is done inside
 	ldr	r0, [tsk, #TI_FLAGS]		@ get new tasks TI_FLAGS
 	tst	r0, #_TIF_NEED_RESCHED
-	moveq	pc, r8				@ go again
+	reteq	r8				@ go again
 	b	1b
 #endif
 
@@ -490,7 +490,7 @@ ENDPROC(__und_usr)
 	.pushsection .fixup, "ax"
 	.align	2
 4:	str     r4, [sp, #S_PC]			@ retry current instruction
-	mov	pc, r9
+	ret	r9
 	.popsection
 	.pushsection __ex_table,"a"
 	.long	1b, 4b
@@ -552,7 +552,7 @@ call_fpe:
 #endif
 	tst	r0, #0x08000000			@ only CDP/CPRT/LDC/STC have bit 27
 	tstne	r0, #0x04000000			@ bit 26 set on both ARM and Thumb-2
-	moveq	pc, lr
+	reteq	lr
 	and	r8, r0, #0x00000f00		@ mask out CP number
  THUMB(	lsr	r8, r8, #8		)
 	mov	r7, #1
@@ -571,33 +571,33 @@ call_fpe:
  THUMB(	add	pc, r8			)
 	nop
 
-	movw_pc	lr				@ CP#0
+	ret.w	lr				@ CP#0
 	W(b)	do_fpe				@ CP#1 (FPE)
 	W(b)	do_fpe				@ CP#2 (FPE)
-	movw_pc	lr				@ CP#3
+	ret.w	lr				@ CP#3
 #ifdef CONFIG_CRUNCH
 	b	crunch_task_enable		@ CP#4 (MaverickCrunch)
 	b	crunch_task_enable		@ CP#5 (MaverickCrunch)
 	b	crunch_task_enable		@ CP#6 (MaverickCrunch)
 #else
-	movw_pc	lr				@ CP#4
-	movw_pc	lr				@ CP#5
-	movw_pc	lr				@ CP#6
+	ret.w	lr				@ CP#4
+	ret.w	lr				@ CP#5
+	ret.w	lr				@ CP#6
 #endif
-	movw_pc	lr				@ CP#7
-	movw_pc	lr				@ CP#8
-	movw_pc	lr				@ CP#9
+	ret.w	lr				@ CP#7
+	ret.w	lr				@ CP#8
+	ret.w	lr				@ CP#9
 #ifdef CONFIG_VFP
 	W(b)	do_vfp				@ CP#10 (VFP)
 	W(b)	do_vfp				@ CP#11 (VFP)
 #else
-	movw_pc	lr				@ CP#10 (VFP)
-	movw_pc	lr				@ CP#11 (VFP)
+	ret.w	lr				@ CP#10 (VFP)
+	ret.w	lr				@ CP#11 (VFP)
 #endif
-	movw_pc	lr				@ CP#12
-	movw_pc	lr				@ CP#13
-	movw_pc	lr				@ CP#14 (Debug)
-	movw_pc	lr				@ CP#15 (Control)
+	ret.w	lr				@ CP#12
+	ret.w	lr				@ CP#13
+	ret.w	lr				@ CP#14 (Debug)
+	ret.w	lr				@ CP#15 (Control)
 
 #ifdef NEED_CPU_ARCHITECTURE
 	.align	2
@@ -649,7 +649,7 @@ ENTRY(fp_enter)
 	.popsection
 
 ENTRY(no_fp)
-	mov	pc, lr
+	ret	lr
 ENDPROC(no_fp)
 
 __und_usr_fault_32:
@@ -745,7 +745,7 @@ ENDPROC(__switch_to)
 #ifdef CONFIG_ARM_THUMB
 	bx	\reg
 #else
-	mov	pc, \reg
+	ret	\reg
 #endif
 	.endm
 
@@ -837,7 +837,7 @@ kuser_cmpxchg64_fixup:
 #if __LINUX_ARM_ARCH__ < 6
 	bcc	kuser_cmpxchg32_fixup
 #endif
-	mov	pc, lr
+	ret	lr
 	.previous
 
 #else
@@ -905,7 +905,7 @@ kuser_cmpxchg32_fixup:
 	subs	r8, r4, r7
 	rsbcss	r8, r8, #(2b - 1b)
 	strcs	r7, [sp, #S_PC]
-	mov	pc, lr
+	ret	lr
 	.previous
 
 #else

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)
@@ -290,15 +291,15 @@ ENDPROC(ftrace_graph_caller_old)
 
 .macro mcount_exit
 	ldmia	sp!, {r0-r3, ip, lr}
-	mov	pc, ip
+	ret	ip
 .endm
 
 ENTRY(__gnu_mcount_nc)
 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

arch/arm/kernel/entry-header.S

@@ -240,12 +240,6 @@
 	movs	pc, lr				@ return & move spsr_svc into cpsr
 	.endm
 
-	@
-	@ 32-bit wide "mov pc, reg"
-	@
-	.macro	movw_pc, reg
-	mov	pc, \reg
-	.endm
 #else	/* CONFIG_THUMB2_KERNEL */
 	.macro	svc_exit, rpsr, irq = 0
 	.if	\irq != 0
@@ -304,14 +298,6 @@
 	movs	pc, lr				@ return & move spsr_svc into cpsr
 	.endm
 #endif	/* ifdef CONFIG_CPU_V7M / else */
-
-	@
-	@ 32-bit wide "mov pc, reg"
-	@
-	.macro	movw_pc, reg
-	mov	pc, \reg
-	nop
-	.endm
 #endif	/* !CONFIG_THUMB2_KERNEL */
 
 /*

arch/arm/kernel/fiqasm.S

@@ -32,7 +32,7 @@ ENTRY(__set_fiq_regs)
 	ldr	lr, [r0]
 	msr	cpsr_c, r1	@ return to SVC mode
 	mov	r0, r0		@ avoid hazard prior to ARMv4
-	mov	pc, lr
+	ret	lr
 ENDPROC(__set_fiq_regs)
 
 ENTRY(__get_fiq_regs)
@@ -45,5 +45,5 @@ ENTRY(__get_fiq_regs)
 	str	lr, [r0]
 	msr	cpsr_c, r1	@ return to SVC mode
 	mov	r0, r0		@ avoid hazard prior to ARMv4
-	mov	pc, lr
+	ret	lr
 ENDPROC(__get_fiq_regs)

arch/arm/kernel/head-common.S

@@ -10,6 +10,7 @@
  * published by the Free Software Foundation.
  *
  */
+#include <asm/assembler.h>
 
 #define ATAG_CORE 0x54410001
 #define ATAG_CORE_SIZE ((2*4 + 3*4) >> 2)
@@ -61,10 +62,10 @@ __vet_atags:
 	cmp	r5, r6
 	bne	1f
 
-2:	mov	pc, lr				@ atag/dtb pointer is ok
+2:	ret	lr				@ atag/dtb pointer is ok
 
 1:	mov	r2, #0
-	mov	pc, lr
+	ret	lr
 ENDPROC(__vet_atags)
 
 /*
@@ -162,7 +163,7 @@ __lookup_processor_type:
 	cmp	r5, r6
 	blo	1b
 	mov	r5, #0				@ unknown processor
-2:	mov	pc, lr
+2:	ret	lr
 ENDPROC(__lookup_processor_type)
 
 /*

arch/arm/kernel/head-nommu.S

@@ -82,7 +82,7 @@ ENTRY(stext)
 	adr	lr, BSYM(1f)			@ return (PIC) address
  ARM(	add	pc, r10, #PROCINFO_INITFUNC	)
  THUMB(	add	r12, r10, #PROCINFO_INITFUNC	)
- THUMB(	mov	pc, r12				)
+ THUMB(	ret	r12				)
  1:	b	__after_proc_init
 ENDPROC(stext)
 
@@ -119,7 +119,7 @@ ENTRY(secondary_startup)
 	mov	r13, r12			@ __secondary_switched address
  ARM(	add	pc, r10, #PROCINFO_INITFUNC	)
  THUMB(	add	r12, r10, #PROCINFO_INITFUNC	)
- THUMB(	mov	pc, r12				)
+ THUMB(	ret	r12				)
 ENDPROC(secondary_startup)
 
 ENTRY(__secondary_switched)
@@ -164,7 +164,7 @@ __after_proc_init:
 #endif
 	mcr	p15, 0, r0, c1, c0, 0		@ write control reg
 #endif /* CONFIG_CPU_CP15 */
-	mov	pc, r13
+	ret	r13
 ENDPROC(__after_proc_init)
 	.ltorg
 
@@ -254,7 +254,7 @@ ENTRY(__setup_mpu)
 	orr	r0, r0, #CR_M			@ Set SCTRL.M (MPU on)
 	mcr	p15, 0, r0, c1, c0, 0		@ Enable MPU
 	isb
-	mov pc,lr
+	ret	lr
 ENDPROC(__setup_mpu)
 #endif
 #include "head-common.S"