[PATCH 3.18 43/47] ARM: 8383/1: nommu: avoid deprecated source register on mov

Greg Kroah-Hartman
2017-04-28T08:40:49Z

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm/kernel/head-nommu.S | 20 +++++++-------------
1 file changed, 7 insertions(+), 13 deletions(-)

--- 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