linux-kernel - [PATCH v3 1/2] arm: perf: Fix callchain parse error with kernel tracepoint events

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Date:	Sat, 2 May 2015 05:42:04 +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:	<wannan0@...wei.com>, <catalin.marinas@....com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: [PATCH v3 1/2] arm: perf: Fix callchain parse error with kernel tracepoint events

For ARM, when tracing with tracepoint events, the IP and cpsr 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 0.006 MB perf.data ]
 ./perf report -f
    Samples: 5  of event 'sched:sched_switch', Event count (approx.): 5 
    Children      Self    Command  Shared Object     Symbol
    100.00%       100.00%  ls       [unknown]         [.] 00000000

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

With this patch, callchain can be parsed correctly as :
	
   .....
-  100.00%   100.00%  ls       [kernel.kallsyms]  [k] __sched_text_start 
   + __sched_text_start 
+   20.00%     0.00%  ls       libc-2.18.so       [.] _dl_addr 
+   20.00%     0.00%  ls       libc-2.18.so       [.] write    
   .....

Jean Pihet found this in ARM and come up with a patch:
http://thread.gmane.org/gmane.linux.kernel/1734283/focus=1734280

This patch rewrite Jean's patch in C.

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

diff --git a/arch/arm/include/asm/perf_event.h b/arch/arm/include/asm/perf_event.h
index d9cf138..4f9dec4 100644
--- a/arch/arm/include/asm/perf_event.h
+++ b/arch/arm/include/asm/perf_event.h
@@ -19,4 +19,11 @@ 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 = SVC_MODE; \
+}
+
 #endif /* __ARM_PERF_EVENT_H__ */
-- 
1.8.3.4

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