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* [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
@ 2021-08-20  5:16 Christophe Leroy
  2021-08-20 12:15 ` Michael Ellerman
  2021-08-27 13:15 ` Michael Ellerman
  0 siblings, 2 replies; 5+ messages in thread
From: Christophe Leroy @ 2021-08-20  5:16 UTC (permalink / raw)
  To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
  Cc: linux-kernel, linuxppc-dev

Copied from commit 89bbe4c798bc ("powerpc/64: indirect function call
use bctrl rather than blrl in ret_from_kernel_thread")

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: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/kernel/entry_32.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 0273a1349006..61fdd53cdd9a 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -161,10 +161,10 @@ ret_from_fork:
 ret_from_kernel_thread:
 	REST_NVGPRS(r1)
 	bl	schedule_tail
-	mtlr	r14
+	mtctr	r14
 	mr	r3,r15
 	PPC440EP_ERR42
-	blrl
+	bctrl
 	li	r3,0
 	b	ret_from_syscall
 
-- 
2.25.0


^ permalink raw reply	[flat|nested] 5+ messages in thread

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2021-08-20  5:16 [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread Christophe Leroy
2021-08-20 12:15 ` Michael Ellerman
2021-08-20 17:18   ` Segher Boessenkool
2021-08-20 18:12     ` Segher Boessenkool
2021-08-27 13:15 ` Michael Ellerman

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