[PATCH] arm: common: document safe usage of arm_setup_stack

[PATCH] arm: common: document safe usage of arm_setup_stack

[Ahmad Fatoum]

Cc: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 arch/arm/include/asm/common.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm/include/asm/common.h b/arch/arm/include/asm/common.h
index c32cdfe5ec2f..72ac988cc131 100644
--- a/arch/arm/include/asm/common.h
+++ b/arch/arm/include/asm/common.h
@@ -46,6 +46,12 @@ static inline unsigned long get_sp(void)
 	return sp;
 }
 
+/*
+ * At least with GCC 7.3.1, listing sp in the clobber register can generate
+ * erroneous accesses to the fp, even in __naked functions. Therefore _always_
+ * branch to a noinline function as soon as possible (usually after relocation
+ * and c_setup).
+ */
 static inline void arm_setup_stack(unsigned long top)
 {
 	__asm__ __volatile__("mov sp, %0"
-- 
2.19.1


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Re: [PATCH] arm: common: document safe usage of arm_setup_stack

[Ahmad Fatoum]

Hello,

On 4/12/18 10:15, Ahmad Fatoum wrote:
> Cc: Lucas Stach <l.stach@pengutronix.de>
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  arch/arm/include/asm/common.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm/include/asm/common.h b/arch/arm/include/asm/common.h
> index c32cdfe5ec2f..72ac988cc131 100644
> --- a/arch/arm/include/asm/common.h
> +++ b/arch/arm/include/asm/common.h
> @@ -46,6 +46,12 @@ static inline unsigned long get_sp(void)
>  	return sp;
>  }
>  
> +/*
> + * At least with GCC 7.3.1, listing sp in the clobber register can generate
> + * erroneous accesses to the fp, even in __naked functions. Therefore _always_
> + * branch to a noinline function as soon as possible (usually after relocation
> + * and c_setup).
> + */
>  static inline void arm_setup_stack(unsigned long top)
>  {
>  	__asm__ __volatile__("mov sp, %0"
> 

any comments?

Cheers
Ahmad

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