[PATCH] [stable v3.18.y] ARM: 8383/1: nommu: avoid deprecated source register on mov

* [PATCH] [stable v3.18.y] ARM: 8383/1: nommu: avoid deprecated source register on mov
@ 2017-04-27 19:32 Arnd Bergmann
  2017-04-28 20:31 ` Stefan Agner
  0 siblings, 1 reply; 2+ messages in thread
From: Arnd Bergmann @ 2017-04-27 19:32 UTC (permalink / raw)
  To: linux-arm-kernel

From: Stefan Agner <stefan@agner.ch>

Commit 970d96f9a81b0dd83ddd8bce0e5e1ba31881c5f5 upstream.

In Thumb2 mode, the stack register r13 is deprecated if the
destination register is the program counter (r15). Similar to
head.S, head-nommu.S uses r13 to store the return address used
after configuring the CPU's CP15 register. However, since we do
not enable a MMU, there will be no address switch and it is
possible to use branch with link instruction to call
__after_proc_init.

Avoid using r13 completely by using bl to call __after_proc_init
and get rid of __secondary_switched.

Beside removing unnecessary complexity, this also fixes a
compiler warning when compiling a !MMU kernel:
Warning: Use of r13 as a source register is deprecated when r15
is the destination register.

Tested-?by: Maxime Coquelin <mcoquelin.stm32@gmail.com>

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
----
I've backported this build fix to 3.18.y as the original
patch did not apply cleanly. I rebased it one patch at a time,
and each step was fairly straightforward, but I did not test
it on hardware, so it would still be nice to have someone else
look over the patch to see if I did something wrong.
---
 arch/arm/kernel/head-nommu.S | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/arch/arm/kernel/head-nommu.S b/arch/arm/kernel/head-nommu.S
index cc176b67c134..c6c66dd4be89 100644
--- a/arch/arm/kernel/head-nommu.S
+++ b/arch/arm/kernel/head-nommu.S
@@ -77,13 +77,12 @@ ENTRY(stext)
 	orr	r6, r6, #(1 << MPU_RSR_EN)	@ Set region enabled bit
 	bl	__setup_mpu
 #endif
-	ldr	r13, =__mmap_switched		@ address to jump to after
-						@ initialising sctlr
 	adr	lr, BSYM(1f)			@ return (PIC) address
  ARM(	add	pc, r10, #PROCINFO_INITFUNC	)
  THUMB(	add	r12, r10, #PROCINFO_INITFUNC	)
  THUMB(	ret	r12				)
- 1:	b	__after_proc_init
+1:	bl	__after_proc_init
+	b	__mmap_switched
 ENDPROC(stext)
 
 #ifdef CONFIG_SMP
@@ -106,8 +105,7 @@ ENTRY(secondary_startup)
 	movs	r10, r5				@ invalid processor?
 	beq	__error_p			@ yes, error 'p'
 
-	adr	r4, __secondary_data
-	ldmia	r4, {r7, r12}
+	ldr	r7, __secondary_data
 
 #ifdef CONFIG_ARM_MPU
 	/* Use MPU region info supplied by __cpu_up */
@@ -115,23 +113,19 @@ ENTRY(secondary_startup)
 	bl      __setup_mpu			@ Initialize the MPU
 #endif
 
-	adr	lr, BSYM(__after_proc_init)	@ return address
-	mov	r13, r12			@ __secondary_switched address
+	adr	lr, BSYM(1f)			@ return (PIC) address
  ARM(	add	pc, r10, #PROCINFO_INITFUNC	)
  THUMB(	add	r12, r10, #PROCINFO_INITFUNC	)
  THUMB(	ret	r12				)
-ENDPROC(secondary_startup)
-
-ENTRY(__secondary_switched)
+1:	bl	__after_proc_init
 	ldr	sp, [r7, #8]			@ set up the stack pointer
 	mov	fp, #0
 	b	secondary_start_kernel
-ENDPROC(__secondary_switched)
+ENDPROC(secondary_startup)
 
 	.type	__secondary_data, %object
 __secondary_data:
 	.long	secondary_data
-	.long	__secondary_switched
 #endif /* CONFIG_SMP */
 
 /*
@@ -164,7 +158,7 @@ __after_proc_init:
 #endif
 	mcr	p15, 0, r0, c1, c0, 0		@ write control reg
 #endif /* CONFIG_CPU_CP15 */
-	ret	r13
+	ret	lr
 ENDPROC(__after_proc_init)
 	.ltorg
 
-- 
2.9.0

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