[PATCH 6.9 126/374] LoongArch: Fix callchain parse error with kernel tracepoint events again

Greg Kroah-Hartman
2024-06-06T14:09:20Z

From: Huacai Chen <chenhuacai@loongson.cn>

[ Upstream commit d6af2c76399f98444a5b4de96baf4b362d9f102b ]

With commit d3119bc985fb645 ("LoongArch: Fix callchain parse error with
kernel tracepoint events"), perf can parse kernel callchain, but not
complete and sometimes maybe error. The reason is LoongArch's unwinders
(guess, prologue and orc) don't really need fp (i.e., regs[22]), and
they use sp (i.e., regs[3]) as the frame address rather than the current
stack pointer.

Fix that by removing the assignment of regs[22], and instead assign the
__builtin_frame_address(0) to regs[3].

Without fix:

Children Self Command Shared Object Symbol
........ ........ ............. ................. ................
33.91% 33.91% swapper [kernel.vmlinux] [k] __schedule
|
|--33.04%--__schedule
|
--0.87%--__arch_cpu_idle
__schedule

With this fix:

Children Self Command Shared Object Symbol
........ ........ ............. ................. ................
31.16% 31.16% swapper [kernel.vmlinux] [k] __schedule
|
|--20.63%--smpboot_entry
| cpu_startup_entry
| schedule_idle
| __schedule
|
--10.53%--start_kernel
cpu_startup_entry
schedule_idle
__schedule

Fixes: d3119bc985fb645 ("LoongArch: Fix callchain parse error with kernel tracepoint events")
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/loongarch/include/asm/perf_event.h | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/loongarch/include/asm/perf_event.h b/arch/loongarch/include/asm/perf_event.h
index 52b638059e40b..f948a0676daf8 100644
--- a/arch/loongarch/include/asm/perf_event.h
+++ b/arch/loongarch/include/asm/perf_event.h
@@ -13,8 +13,7 @@

#define perf_arch_fetch_caller_regs(regs, __ip) { \
(regs)->csr_era = (__ip); \
- (regs)->regs[3] = current_stack_pointer; \
- (regs)->regs[22] = (unsigned long) __builtin_frame_address(0); \
+ (regs)->regs[3] = (unsigned long) __builtin_frame_address(0); \
}

#endif /* __LOONGARCH_PERF_EVENT_H__ */
--
2.43.0