linux-kernel - [PATCH 2/3] tracing: evaluate len expression only once in __dynamic

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Date:	Fri, 28 Feb 2014 21:32:17 -0800
From:	Filipe Brandenburger <filbranden@...gle.com>
To:	Steven Rostedt <rostedt@...dmis.org>, Li Zefan <lizefan@...wei.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Filipe Brandenburger <filbranden@...gle.com>
Subject: [PATCH 2/3] tracing: evaluate len expression only once in __dynamic_array macro

Use a temporary variable to store the expansion of the len expression.
If the evaluation is expensive, this commit will ensure it is evaluated
only once inside ftrace_get_offsets_<call>.

Signed-off-by: Filipe Brandenburger <filbranden@...gle.com>
---
 include/trace/ftrace.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 82e8d89..86a056a 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -373,10 +373,11 @@ ftrace_define_fields_##call(struct ftrace_event_call *event_call)	\
 
 #undef __dynamic_array
 #define __dynamic_array(type, item, len)				\
+	__item_length = (len) * sizeof(type);				\
 	__data_offsets->item = __data_size +				\
 			       offsetof(typeof(*entry), __data);	\
-	__data_offsets->item |= ((len) * sizeof(type)) << 16;		\
-	__data_size += (len) * sizeof(type);
+	__data_offsets->item |= __item_length << 16;			\
+	__data_size += __item_length;
 
 #undef __string
 #define __string(item, src) __dynamic_array(char, item,			\
@@ -388,6 +389,7 @@ static inline notrace int ftrace_get_offsets_##call(			\
 	struct ftrace_data_offsets_##call *__data_offsets, proto)       \
 {									\
 	int __data_size = 0;						\
+	int __maybe_unused __item_length;				\
 	struct ftrace_raw_##call __maybe_unused *entry;			\
 									\
 	tstruct;							\
-- 
1.9.0.279.gdc9e3eb

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