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

[Ism Hong]

For RISC-V, when tracing with tracepoint events, the IP and status are
set to 0, preventing the perf code parsing the callchain and resolving
the symbols correctly.

 ./ply 'tracepoint:kmem/kmem_cache_alloc { @[stack]=count(); }'
 @:
 { <STACKID4294967282> }: 1

The fix is to implement perf_arch_fetch_caller_regs for riscv, which
fills several necessary registers used for callchain unwinding,
including epc, sp, s0 and status. It's similar to commit b3eac0265bf6
("arm: perf: Fix callchain parse error with kernel tracepoint events")
and commit 5b09a094f2fb ("arm64: perf: Fix callchain parse error with
kernel tracepoint events").

With this patch, callchain can be parsed correctly as:

 ./ply 'tracepoint:kmem/kmem_cache_alloc { @[stack]=count(); }'
 @:
 {
         __traceiter_kmem_cache_alloc+68
         __traceiter_kmem_cache_alloc+68
         kmem_cache_alloc+354
         __sigqueue_alloc+94
         __send_signal_locked+646
         send_signal_locked+154
         do_send_sig_info+84
         __kill_pgrp_info+130
         kill_pgrp+60
         isig+150
         n_tty_receive_signal_char+36
         n_tty_receive_buf_standard+2214
         n_tty_receive_buf_common+280
         n_tty_receive_buf2+26
         tty_ldisc_receive_buf+34
         tty_port_default_receive_buf+62
         flush_to_ldisc+158
         process_one_work+458
         worker_thread+138
         kthread+178
         riscv_cpufeature_patch_func+832
  }: 1

This patch works both on RV32/RV64.

Signed-off-by: Ism Hong <ism.hong at gmail.com>
---
 arch/riscv/include/asm/perf_event.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/riscv/include/asm/perf_event.h b/arch/riscv/include/asm/perf_event.h
index d42c901f9a97..665bbc9b2f84 100644
--- a/arch/riscv/include/asm/perf_event.h
+++ b/arch/riscv/include/asm/perf_event.h
@@ -10,4 +10,11 @@
 
 #include <linux/perf_event.h>
 #define perf_arch_bpf_user_pt_regs(regs) (struct user_regs_struct *)regs
+
+#define perf_arch_fetch_caller_regs(regs, __ip) { \
+	(regs)->epc = (__ip); \
+	(regs)->s0 = (unsigned long) __builtin_frame_address(0); \
+	(regs)->sp = current_stack_pointer; \
+	(regs)->status = SR_PP; \
+}
 #endif /* _ASM_RISCV_PERF_EVENT_H */
-- 
2.37.2