[PATCH] [stable v3.18.y] ARM: 8383/1: nommu: avoid deprecated source register on mov
Stefan Agner
stefan at agner.ch
Fri Apr 28 16:31:14 EDT 2017
On 2017-04-27 12:32, Arnd Bergmann wrote:
> From: Stefan Agner <stefan at 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 at gmail.com>
>
> Signed-off-by: Stefan Agner <stefan at agner.ch>
> Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
> Signed-off-by: Arnd Bergmann <arnd at 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.
Looks good to me.
--
Stefan
> ---
> 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
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