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Subject[PATCH 3/3] tracing: introduce a trace_data_offset struct to store array size
Date
Commit 7d536cb3f stores the length of the array in the high 16 bits of
the offset field. Using a struct with two separate 16 bit fields makes
it cleaner.

Tested: Boot kernel with this change, set a 'filename ~ "/usr/bin/pst*"'
regex filter on events/sched/sched_process_exec/filter, enabled tracing,
checked that calling pstree would log the trace event as expected.

Signed-off-by: Filipe Brandenburger <filbranden@google.com>
---
include/linux/ftrace_event.h | 5 +++++
include/trace/ftrace.h | 28 ++++++++++++++--------------
kernel/trace/trace_events_filter.c | 13 ++++++++++---
3 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 4e4cc28..67e4122 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -123,6 +123,11 @@ struct trace_event {
struct trace_event_functions *funcs;
};

+struct trace_array_offset {
+ u16 offset;
+ u16 length;
+};
+
extern int register_ftrace_event(struct trace_event *event);
extern int unregister_ftrace_event(struct trace_event *event);

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 86a056a..eac4d0a 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -48,7 +48,8 @@
#define __array(type, item, len) type item[len];

#undef __dynamic_array
-#define __dynamic_array(type, item, len) u32 __data_loc_##item;
+#define __dynamic_array(type, item, len) \
+ struct trace_array_offset __data_loc_##item;

#undef __string
#define __string(item, src) __dynamic_array(char, item, -1)
@@ -103,14 +104,14 @@
* Include the following:
*
* struct ftrace_data_offsets_<call> {
- * u32 <item1>;
- * u32 <item2>;
+ * struct trace_array_offset <item1>;
+ * struct trace_array_offset <item2>;
* [...]
* };
*
- * The __dynamic_array() macro will create each u32 <item>, this is
- * to keep the offset of each array from the beginning of the event.
- * The size of an array is also encoded, in the higher 16 bits of <item>.
+ * The __dynamic_array() macro will create each trace_array_offset <item>, this
+ * is to keep the offset and length of each array from the beginning of the
+ * event.
*/

#undef __field
@@ -123,7 +124,8 @@
#define __array(type, item, len)

#undef __dynamic_array
-#define __dynamic_array(type, item, len) u32 item;
+#define __dynamic_array(type, item, len) \
+ struct trace_array_offset item;

#undef __string
#define __string(item, src) __dynamic_array(char, item, -1)
@@ -195,7 +197,7 @@

#undef __get_dynamic_array
#define __get_dynamic_array(field) \
- ((void *)__entry + (__entry->__data_loc_##field & 0xffff))
+ ((void *)__entry + __entry->__data_loc_##field.offset)

#undef __get_str
#define __get_str(field) (char *)__get_dynamic_array(field)
@@ -373,11 +375,10 @@ 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 + \
+ __data_offsets->item.offset = __data_size + \
offsetof(typeof(*entry), __data); \
- __data_offsets->item |= __item_length << 16; \
- __data_size += __item_length;
+ __data_offsets->item.length = (len) * sizeof(type); \
+ __data_size += __data_offsets->item.length;

#undef __string
#define __string(item, src) __dynamic_array(char, item, \
@@ -389,7 +390,6 @@ 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; \
@@ -658,7 +658,7 @@ __attribute__((section("_ftrace_events"))) *__event_##call = &event_##call

#undef __get_dynamic_array
#define __get_dynamic_array(field) \
- ((void *)__entry + (__entry->__data_loc_##field & 0xffff))
+ ((void *)__entry + __entry->__data_loc_##field.offset)

#undef __get_str
#define __get_str(field) (char *)__get_dynamic_array(field)
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 8a86319..805fc0d 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -234,12 +234,19 @@ static int filter_pred_pchar(struct filter_pred *pred, void *event)
*/
static int filter_pred_strloc(struct filter_pred *pred, void *event)
{
- u32 str_item = *(u32 *)(event + pred->offset);
- int str_loc = str_item & 0xffff;
- int str_len = str_item >> 16;
+ struct trace_array_offset *array_offset =
+ (struct trace_array_offset *)(event + pred->offset);
+ int str_loc = array_offset->offset;
+ int str_len = array_offset->length;
char *addr = (char *)(event + str_loc);
int cmp, match;

+ /*
+ * As struct trace_array_offset is replacing an u32,
+ * ensure they have the same size.
+ */
+ BUILD_BUG_ON(sizeof(struct trace_array_offset) != sizeof(u32));
+
cmp = pred->regex.match(addr, &pred->regex, str_len);

match = cmp ^ pred->not;
--
1.9.0.279.gdc9e3eb


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