[PATCH 11/18] tracing: Add symbol type to function based events

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>

Add a special type "symbol" that will use %pS to display the field of a
function based event.

Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 Documentation/trace/function-based-events.rst | 26 +++++++++++++++++++++++++-
 kernel/trace/trace_event_ftrace.c             | 13 ++++++++++---
 2 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/Documentation/trace/function-based-events.rst b/Documentation/trace/function-based-events.rst
index bdb28f433bfb..f18c8f3ef330 100644
--- a/Documentation/trace/function-based-events.rst
+++ b/Documentation/trace/function-based-events.rst
@@ -98,7 +98,8 @@ as follows:
  ATOM := 'u8' | 'u16' | 'u32' | 'u64' |
          's8' | 's16' | 's32' | 's64' |
          'x8' | 'x16' | 'x32' | 'x64' |
-         'char' | 'short' | 'int' | 'long' | 'size_t'
+         'char' | 'short' | 'int' | 'long' | 'size_t' |
+	 'symbol'
 
  FIELD := <name> | <name> INDEX | <name> OFFSET | <name> OFFSET INDEX
 
@@ -243,3 +244,26 @@ The above will take the parameter value, add it by 4, then index it by two
 8 byte words. It's the same in C as: (u64 *)((void *)param + 4)[2]
 
  Note: "int skb[32]" is the same as "int skb+4[31]".
+
+
+Symbols (function names)
+========================
+
+To display kallsyms "%pS" type of output, use the special type "symbol".
+
+Again, using gdb to find the offset of the "func" field of struct work_struct
+
+(gdb) printf "%d\n", &((struct work_struct *)0)->func
+24
+
+ Both "symbol func[3]" and "symbol func+24[0]" will work.
+
+ # echo '__queue_work(int cpu, x64 wq, symbol func[3])' > function_events
+
+ # echo 1 > events/functions/__queue_work/enable
+ # cat trace
+       bash-1641  [007] d..2  6241.171332: queue_work_on->__queue_work(cpu=128, wq=ffff88011a010e00, func=flush_to_ldisc+0x0/0xa0)
+       bash-1641  [007] d..2  6241.171460: queue_work_on->__queue_work(cpu=128, wq=ffff88011a010e00, func=flush_to_ldisc+0x0/0xa0)
+     <idle>-0     [000] dNs3  6241.172004: delayed_work_timer_fn->__queue_work(cpu=128, wq=ffff88011a010800, func=vmstat_shepherd+0x0/0xb0)
+ worker/0:2-1689  [000] d..2  6241.172026: __queue_delayed_work->__queue_work(cpu=7, wq=ffff88011a11da00, func=vmstat_update+0x0/0x70)
+     <idle>-0     [005] d.s3  6241.347996: queue_work_on->__queue_work(cpu=128, wq=ffff88011a011200, func=fb_flashcursor+0x0/0x110 [fb])
diff --git a/kernel/trace/trace_event_ftrace.c b/kernel/trace/trace_event_ftrace.c
index 0f2650e97e49..ba10177b9bd6 100644
--- a/kernel/trace/trace_event_ftrace.c
+++ b/kernel/trace/trace_event_ftrace.c
@@ -76,6 +76,7 @@ typedef u64 x64;
 typedef u32 x32;
 typedef u16 x16;
 typedef u8 x8;
+typedef void * symbol;
 
 #define TYPE_TUPLE(type)			\
 	{ #type, sizeof(type), is_signed_type(type) }
@@ -97,7 +98,8 @@ typedef u8 x8;
 	TYPE_TUPLE(x16),			\
 	TYPE_TUPLE(u8),				\
 	TYPE_TUPLE(s8),				\
-	TYPE_TUPLE(x8)
+	TYPE_TUPLE(x8),				\
+	TYPE_TUPLE(symbol)
 
 static struct func_type {
 	char		*name;
@@ -262,7 +264,7 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
 	switch (state) {
 	case FUNC_STATE_INIT:
 		unsign = 0;
-		if (!isalpha(token[0]))
+		if (!isalpha(token[0]) && token[0] != '_')
 			break;
 		/* Do not allow wild cards */
 		if (strstr(token, "*") || strstr(token, "?"))
@@ -305,7 +307,7 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
 		return FUNC_STATE_TYPE;
 
 	case FUNC_STATE_TYPE:
-		if (!isalpha(token[0]))
+		if (!isalpha(token[0]) || token[0] == '_')
 			break;
 		if (WARN_ON(!fevent->last_arg))
 			break;
@@ -472,6 +474,11 @@ static void make_fmt(struct func_arg *arg, char *fmt)
 {
 	int c = 0;
 
+	if (arg->func_type == FUNC_TYPE_symbol) {
+		strcpy(fmt, "%pS");
+		return;
+	}
+
 	fmt[c++] = '%';
 
 	if (arg->size == 8) {
-- 
2.15.1