linux-kernel - [PATCH 5/7] perf: Make perf_fetch_caller_regs rewind to the first caller only

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Message-Id: <1269568362-13690-6-git-send-regression-fweisbec@gmail.com>
Date:	Fri, 26 Mar 2010 02:52:40 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	David Miller <davem@...emloft.net>,
	Archs <linux-arch@...r.kernel.org>
Subject: [PATCH 5/7] perf: Make perf_fetch_caller_regs rewind to the first caller only

Trace events now only need to rewind the regs to the immediate
caller, so we don't need anymore to implement the support for
further stack walking.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: David Miller <davem@...emloft.net>
Cc: Archs <linux-arch@...r.kernel.org>
---
 arch/x86/include/asm/perf_event.h |    6 +++---
 arch/x86/include/asm/stacktrace.h |    5 ++---
 include/linux/perf_event.h        |   30 +++++-------------------------
 include/trace/ftrace.h            |    2 +-
 4 files changed, 11 insertions(+), 32 deletions(-)

diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 4bf3d37..1df2317 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -157,9 +157,9 @@ extern void perf_events_lapic_init(void);
 
 #include <asm/stacktrace.h>
 
-#define perf_arch_fetch_caller_regs(regs, ip, skip)	\
-	(regs)->ip = ip;				\
-	(regs)->bp = rewind_frame_pointer(skip);	\
+#define perf_arch_fetch_caller_regs(regs, __ip)		\
+	(regs)->ip = __ip;				\
+	(regs)->bp = caller_frame_pointer();		\
 	(regs)->cs = __KERNEL_CS;			\
 	local_save_flags((regs)->flags);
 
diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index 8fb70b7..62c9897 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -74,15 +74,14 @@ struct stack_frame {
 	unsigned long return_address;
 };
 
-static inline unsigned long rewind_frame_pointer(int n)
+static inline unsigned long caller_frame_pointer(void)
 {
 	struct stack_frame *frame;
 
 	get_bp(frame);
 
 #ifdef CONFIG_FRAME_POINTER
-	while (n--)
-		frame = frame->next_frame;
+	frame = frame->next_frame;
 #endif
 
 	return (unsigned long)frame;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 76b680f..3b59cf7 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -869,42 +869,22 @@ perf_sw_event(u32 event_id, u64 nr, int nmi, struct pt_regs *regs, u64 addr)
 
 #ifndef perf_arch_fetch_caller_regs
 static inline void
-perf_arch_fetch_caller_regs(struct pt_regs *regs, unsigned long ip, int skip){ }
+perf_arch_fetch_caller_regs(struct pt_regs *regs, unsigned long ip) { }
 #endif
 
 /*
- * Take a snapshot of the regs. Skip ip and frame pointer to
- * the nth caller. We only need a few of the regs:
+ * Take a snapshot of the regs. Rewind ip and frame pointer to
+ * the caller. We only need a few of the regs:
  * - ip for PERF_SAMPLE_IP
  * - cs for user_mode() tests
  * - bp for callchains
  * - eflags, for future purposes, just in case
  */
-static inline void perf_fetch_caller_regs(struct pt_regs *regs, int skip)
+static inline void perf_fetch_caller_regs(struct pt_regs *regs)
 {
-	unsigned long ip;
-
 	memset(regs, 0, sizeof(*regs));
 
-	switch (skip) {
-	case 1 :
-		ip = CALLER_ADDR0;
-		break;
-	case 2 :
-		ip = CALLER_ADDR1;
-		break;
-	case 3 :
-		ip = CALLER_ADDR2;
-		break;
-	case 4:
-		ip = CALLER_ADDR3;
-		break;
-	/* No need to support further for now */
-	default:
-		ip = 0;
-	}
-
-	perf_arch_fetch_caller_regs(regs, ip, skip);
+	perf_arch_fetch_caller_regs(regs, CALLER_ADDR0);
 }
 
 extern void __perf_event_mmap(struct vm_area_struct *vma);
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 882c648..82e9977 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -795,7 +795,7 @@ static notrace void perf_trace_##call(proto)				\
 	struct ftrace_event_call *event_call = &event_##call;		\
 	struct pt_regs *__regs = &get_cpu_var(perf_trace_regs);		\
 									\
-	perf_fetch_caller_regs(__regs, 1);				\
+	perf_fetch_caller_regs(__regs);					\
 									\
 	perf_trace_templ_##template(event_call, __regs, args);		\
 									\
-- 
1.6.2.3

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