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Subject[PATCH 2/3] tracing: evaluate len expression only once in __dynamic_array macro
Date
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@google.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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