* [PATCH] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
@ 2020-06-11 12:11 Nicholas Piggin
2020-06-11 12:26 ` Christophe Leroy
2020-06-26 4:46 ` Michael Ellerman
0 siblings, 2 replies; 4+ messages in thread
From: Nicholas Piggin @ 2020-06-11 12:11 UTC (permalink / raw)
To: linuxppc-dev; +Cc: Nicholas Piggin
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.
Signed-off-by: Nicholas Piggin <npiggin@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
--
2.23.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
2020-06-11 12:11 [PATCH] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread Nicholas Piggin
@ 2020-06-11 12:26 ` Christophe Leroy
2020-06-14 9:24 ` Nicholas Piggin
2020-06-26 4:46 ` Michael Ellerman
1 sibling, 1 reply; 4+ messages in thread
From: Christophe Leroy @ 2020-06-11 12:26 UTC (permalink / raw)
To: Nicholas Piggin, linuxppc-dev
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@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
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
2020-06-11 12:26 ` Christophe Leroy
@ 2020-06-14 9:24 ` Nicholas Piggin
0 siblings, 0 replies; 4+ messages in thread
From: Nicholas Piggin @ 2020-06-14 9:24 UTC (permalink / raw)
To: Christophe Leroy, linuxppc-dev
Excerpts from Christophe Leroy's message of June 11, 2020 10:26 pm:
>
>
> 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 ?
Yes I would say so. I don't know much about 32-bit implementations but
MPC7450 at least has a link stack predictor.
Thanks,
Nick
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
2020-06-11 12:11 [PATCH] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread Nicholas Piggin
2020-06-11 12:26 ` Christophe Leroy
@ 2020-06-26 4:46 ` Michael Ellerman
1 sibling, 0 replies; 4+ messages in thread
From: Michael Ellerman @ 2020-06-26 4:46 UTC (permalink / raw)
To: linuxppc-dev, Nicholas Piggin
On Thu, 11 Jun 2020 22:11:19 +1000, Nicholas Piggin wrote:
> 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.
Applied to powerpc/next.
[1/1] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
https://git.kernel.org/powerpc/c/89bbe4c798bc3a43c882179adb5222c1a972ac70
cheers
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-06-26 5:11 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-06-11 12:11 [PATCH] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread Nicholas Piggin
2020-06-11 12:26 ` Christophe Leroy
2020-06-14 9:24 ` Nicholas Piggin
2020-06-26 4:46 ` Michael Ellerman
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.