[PATCH] LoongArch: Fix callchain parse error with kernel tracepoint events

[Huacai Chen]

In order to fix perf's callchain parse error for LoongArch, we implement
perf_arch_fetch_caller_regs() which fills several necessary registers
used for callchain unwinding, including sp, fp, and era. This is similar
to the following commits.

commit b3eac0265bf6:
("arm: perf: Fix callchain parse error with kernel tracepoint events")

commit 5b09a094f2fb:
("arm64: perf: Fix callchain parse error with kernel tracepoint events")

commit 9a7e8ec0d4cc:
("riscv: perf: Fix callchain parse error with kernel tracepoint events")

Test with commands:

 perf record -e sched:sched_switch -g --call-graph dwarf
 perf report

Without this patch:

 Children      Self  Command        Shared Object      Symbol
 ........  ........  .............  .................  ....................

 43.41%    43.41%  swapper          [unknown]          [k] 0000000000000000

 10.94%    10.94%  loong-container  [unknown]          [k] 0000000000000000
         |
         |--5.98%--0x12006ba38
         |
         |--2.56%--0x12006bb84
         |
          --2.40%--0x12006b6b8

With this patch, callchain can be parsed correctly:

 Children      Self  Command        Shared Object      Symbol
 ........  ........  .............  .................  ....................

 47.57%    47.57%  swapper          [kernel.vmlinux]   [k] __schedule
         |
         ---__schedule

 26.76%    26.76%  loong-container  [kernel.vmlinux]   [k] __schedule
         |
         |--13.78%--0x12006ba38
         |          |
         |          |--9.19%--__schedule
         |          |
         |           --4.59%--handle_syscall
         |                     do_syscall
         |                     sys_futex
         |                     do_futex
         |                     futex_wait
         |                     futex_wait_queue_me
         |                     hrtimer_start_range_ns
         |                     __schedule
         |
         |--8.38%--0x12006bb84
         |          handle_syscall
         |          do_syscall
         |          sys_epoll_pwait
         |          do_epoll_wait
         |          schedule_hrtimeout_range_clock
         |          hrtimer_start_range_ns
         |          __schedule
         |
          --4.59%--0x12006b6b8
                    handle_syscall
                    do_syscall
                    sys_nanosleep
                    hrtimer_nanosleep
                    do_nanosleep
                    hrtimer_start_range_ns
                    __schedule

Reported-by: Youling Tang <tangyouling@xxxxxxxxxx>
Suggested-by: Youling Tang <tangyouling@xxxxxxxxxx>
Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
---
 arch/loongarch/include/asm/perf_event.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/loongarch/include/asm/perf_event.h b/arch/loongarch/include/asm/perf_event.h
index 2a35a0bc2aaa..157c4ace69d0 100644
--- a/arch/loongarch/include/asm/perf_event.h
+++ b/arch/loongarch/include/asm/perf_event.h
@@ -9,4 +9,10 @@
 
 #define perf_arch_bpf_user_pt_regs(regs) (struct user_pt_regs *)regs
 
+#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); \
+}
+
 #endif /* __LOONGARCH_PERF_EVENT_H__ */
-- 
2.43.0