linux-kernel - [PATCH v3 2/2] arm64: perf: Fix callchain parse error with kernel tracepoint events

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Date:	Sat, 2 May 2015 05:58:17 +0000
From:	Hou Pengyang <houpengyang@...wei.com>
To:	<will.deacon@....com>, <a.p.zijlstra@...llo.nl>,
	<paulus@...ba.org>, <acme@...nel.org>, <mingo@...hat.com>
CC:	<wangnan0@...wei.com>, <catalin.marinas@....com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: [PATCH v3 2/2] arm64: perf: Fix callchain parse error with kernel tracepoint events

For ARM64, when tracing with tracepoint events, the IP and pstate are set
to 0, preventing the perf code parsing the callchain and resolving the
symbols correctly.

 ./perf record -e sched:sched_switch -g --call-graph dwarf ls
    [ perf record: Captured and wrote 0.146 MB perf.data ]
 ./perf report -f
    Samples: 194  of event 'sched:sched_switch', Event count (approx.): 194
    Children      Self    Command  Shared Object     Symbol
    100.00%       100.00%  ls       [unknown]         [.] 0000000000000000

The fix is to implement perf_arch_fetch_caller_regs for ARM64, which fills
several necessary registers used for callchain unwinding, including pc,sp,
fp and spsr .

With this patch, callchain can be parsed correctly as follows:

     ......
+    2.63%     0.00%  ls       [kernel.kallsyms]  [k] vfs_symlink
+    2.63%     0.00%  ls       [kernel.kallsyms]  [k] follow_down
+    2.63%     0.00%  ls       [kernel.kallsyms]  [k] pfkey_get
+    2.63%     0.00%  ls       [kernel.kallsyms]  [k] do_execveat_common.isra.33
-    2.63%     0.00%  ls       [kernel.kallsyms]  [k] pfkey_send_policy_notify
     pfkey_send_policy_notify
     pfkey_get
     v9fs_vfs_rename
     page_follow_link_light
     link_path_walk
     el0_svc_naked
    .......

Signed-off-by: Hou Pengyang <houpengyang@...wei.com>
---
 arch/arm64/include/asm/perf_event.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h
index d26d1d5..cc92021 100644
--- a/arch/arm64/include/asm/perf_event.h
+++ b/arch/arm64/include/asm/perf_event.h
@@ -24,4 +24,11 @@ extern unsigned long perf_misc_flags(struct pt_regs *regs);
 #define perf_misc_flags(regs)	perf_misc_flags(regs)
 #endif
 
+#define perf_arch_fetch_caller_regs(regs, __ip) { \
+	(regs)->ARM_pc = (__ip);    \
+	(regs)->ARM_fp = (unsigned long) __builtin_frame_address(0); \
+	(regs)->ARM_sp = current_stack_pointer; \
+	(regs)->ARM_cpsr = PSR_MODE_EL1h;	\
+}
+
 #endif
-- 
1.8.3.4

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