[PATCH 2/2] powerpc/pseries: Remove unused hcall tracing instruction

Nicholas Piggin npiggin at gmail.com
Tue May 9 19:16:00 AEST 2023

When JUMP_LABEL=n, the tracepoint refcount test in the pre-call stores
the refcount value to the stack, so the same value can be used for the
post-call (presumably to avoid racing with the value concurrently

On little-endian (ELFv2) that might have just worked by luck, because
32(r1) is STK_PARAM(R3) there and so the value save gets clobbered by
the tracing code when it's non-zero, but fortunately r3 is the hcall
number and 0 is an invalid hcall number so it should get clobbered by
another non-zero value. In any case, commit cc1adb5f32557
("powerpc/pseries: Use jump labels for hcall tracepoints") removed the
code that actually used the value stored, so now it's just dead code.

It's fragile to be storing to the stack like this, and confusing. Better
remove it.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
 arch/powerpc/platforms/pseries/hvCall.S | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/hvCall.S b/arch/powerpc/platforms/pseries/hvCall.S
index ca0674b0b683..bae45b358a09 100644
--- a/arch/powerpc/platforms/pseries/hvCall.S
+++ b/arch/powerpc/platforms/pseries/hvCall.S
@@ -92,7 +92,6 @@ BEGIN_FTR_SECTION;						\
 END_FTR_SECTION(0, 1);						\
 	LOAD_REG_ADDR(r12, hcall_tracepoint_refcount) ;		\
 	ld	r12,0(r12);					\
-	std	r12,32(r1);					\
 	cmpdi	r12,0;						\
 	bne-	LABEL;						\

More information about the Linuxppc-dev mailing list