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Subject[PATCH 07/18] tracing: Add dereferencing multiple fields per arg
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

As an argument may be a structure or an array, we may want to dereference
more than one field per argument. Create a pipe '|' token to the parsing
that allows to reference multipe dereference fields per function argument.

Change func_arg fields from char to s8 or u8 to allow them to be
subscripts to arrays.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
Documentation/trace/function-based-events.rst | 20 +++++++++++++++++-
kernel/trace/trace_event_ftrace.c | 29 ++++++++++++++++++++-------
2 files changed, 41 insertions(+), 8 deletions(-)

diff --git a/Documentation/trace/function-based-events.rst b/Documentation/trace/function-based-events.rst
index 7d67229e8e88..2a002c8a500b 100644
--- a/Documentation/trace/function-based-events.rst
+++ b/Documentation/trace/function-based-events.rst
@@ -91,7 +91,7 @@ as follows:

ARGS := ARG | ARG ',' ARGS | ''

- ARG := TYPE FIELD
+ ARG := TYPE FIELD | ARG '|' ARG

TYPE := ATOM

@@ -158,3 +158,21 @@ As 128 / 4 (length of int) is 32, we can see the length of the skb with:
<idle>-0 [003] ..s3 280.807023: __netif_receive_skb_core->ip_rcv(skb=52, dev=ffff8801092f9400)

Now we see the length of the sk_buff per event.
+
+
+Multiple fields per argument
+============================
+
+
+If we still want to see the skb pointer value along with the length of the
+skb, then using the '|' option allows us to add more than one option to
+an argument:
+
+ # echo 'ip_rcv(x64 skb | int skb[32], x64 dev)' > function_events
+
+ # echo 1 > events/functions/ip_rcv/enable
+ # cat trace
+ <idle>-0 [003] ..s3 904.075838: __netif_receive_skb_core->ip_rcv(skb=ffff88011396e800, skb=52, dev=ffff880115204000)
+ <idle>-0 [003] ..s3 904.075848: __netif_receive_skb_core->ip_rcv(skb=ffff88011396e800, skb=52, dev=ffff880115204000)
+ <idle>-0 [003] ..s3 904.725486: __netif_receive_skb_core->ip_rcv(skb=ffff88011396e800, skb=194, dev=ffff880115204000)
+ <idle>-0 [003] ..s3 905.152537: __netif_receive_skb_core->ip_rcv(skb=ffff88011396f200, skb=88, dev=ffff880115204000)
diff --git a/kernel/trace/trace_event_ftrace.c b/kernel/trace/trace_event_ftrace.c
index 5d37498d1c6b..8c9d4a92deab 100644
--- a/kernel/trace/trace_event_ftrace.c
+++ b/kernel/trace/trace_event_ftrace.c
@@ -21,8 +21,8 @@ struct func_arg {
long indirect;
short offset;
short size;
- char arg;
- char sign;
+ s8 arg;
+ u8 sign;
};

struct func_event {
@@ -60,6 +60,7 @@ enum func_states {
FUNC_STATE_BRACKET,
FUNC_STATE_BRACKET_END,
FUNC_STATE_INDIRECT,
+ FUNC_STATE_PIPE,
FUNC_STATE_TYPE,
FUNC_STATE_VAR,
FUNC_STATE_COMMA,
@@ -179,6 +180,7 @@ static char *next_token(char **ptr, char *last)
*str == '[' ||
*str == ']' ||
*str == ',' ||
+ *str == '|' ||
*str == ')')
break;
}
@@ -251,11 +253,15 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
break;
return FUNC_STATE_PARAM;

+ case FUNC_STATE_PIPE:
+ fevent->arg_cnt--;
+ goto comma;
case FUNC_STATE_PARAM:
if (token[0] == ')')
return FUNC_STATE_END;
/* Fall through */
case FUNC_STATE_COMMA:
+ comma:
for (i = 0; func_types[i].size; i++) {
if (strcmp(token, func_types[i].name) == 0)
break;
@@ -297,6 +303,8 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
return FUNC_STATE_END;
case ',':
return FUNC_STATE_COMMA;
+ case '|':
+ return FUNC_STATE_PIPE;
}
break;

@@ -306,6 +314,8 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
return FUNC_STATE_END;
case ',':
return FUNC_STATE_COMMA;
+ case '|':
+ return FUNC_STATE_PIPE;
case '[':
return FUNC_STATE_BRACKET;
}
@@ -364,7 +374,6 @@ static void func_event_trace(struct trace_event_file *trace_file,
int nr_args;
int size;
int pc;
- int i = 0;

if (trace_trigger_soft_disabled(trace_file))
return;
@@ -386,8 +395,8 @@ static void func_event_trace(struct trace_event_file *trace_file,
nr_args = arch_get_func_args(pt_regs, 0, func_event->arg_cnt, args);

list_for_each_entry(arg, &func_event->args, list) {
- if (i < nr_args)
- val = get_arg(arg, args[i]);
+ if (arg->arg < nr_args)
+ val = get_arg(arg, args[arg->arg]);
else
val = 0;
memcpy(&entry->data[arg->offset], &val, arg->size);
@@ -741,12 +750,18 @@ static int func_event_seq_show(struct seq_file *m, void *v)
struct func_event *func_event = v;
struct func_arg *arg;
bool comma = false;
+ int last_arg = 0;

seq_printf(m, "%s(", func_event->func);

list_for_each_entry(arg, &func_event->args, list) {
- if (comma)
- seq_puts(m, ", ");
+ if (comma) {
+ if (last_arg == arg->arg)
+ seq_puts(m, " | ");
+ else
+ seq_puts(m, ", ");
+ }
+ last_arg = arg->arg;
comma = true;
seq_printf(m, "%s %s", arg->type, arg->name);
if (arg->indirect && arg->size)
--
2.15.1

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