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

Steven Rostedt
2018-02-02T23:05:09Z

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From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

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@goodmis.org>
---
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