[PATCH] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread

[Christophe Leroy]

Le 11/06/2020 à 14:11, Nicholas Piggin a écrit :
> blrl is not recommended to use as an indirect function call, as it may
> corrupt the link stack predictor.
> 
> This is not a performance critical path but this should be fixed for
> consistency.

There's exactly the same in entry_32.S
Should it be changed there too ... for consistency :) ?

ppc32 also uses blrl for calling syscall handler, should it be changed 
as well ?

Christophe

> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>   arch/powerpc/kernel/entry_64.S | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index 223c4f008e63..f59a17471d4d 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -400,12 +400,12 @@ _GLOBAL(ret_from_fork)
>   _GLOBAL(ret_from_kernel_thread)
>   	bl	schedule_tail
>   	REST_NVGPRS(r1)
> -	mtlr	r14
> +	mtctr	r14
>   	mr	r3,r15
>   #ifdef PPC64_ELF_ABI_v2
>   	mr	r12,r14
>   #endif
> -	blrl
> +	bctrl
>   	li	r3,0
>   	b	.Lsyscall_exit
>   
>