linux-kernel - perf/tracepoints access to interpreted strings

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Date:	Wed, 15 Apr 2015 10:20:08 -0600
From:	David Ahern <dsahern@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: perf/tracepoints access to interpreted strings

Hi Steve:

I was hoping you could provide points on how to get access to an 
interpreted field in a tracepoint within perf.

This is an example of the tracepoint:

# cat /sys/kernel/debug/tracing/events/irq/softirq_exit/format
name: softirq_exit
ID: 99
format:
	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	field:int common_pid;	offset:4;	size:4;	signed:1;
	field:int common_padding;	offset:8;	size:4;	signed:1;

	field:unsigned int vec;	offset:12;	size:4;	signed:0;

print fmt: "vec=%u [action=%s]", REC->vec, __print_symbolic(REC->vec, { 
HI_SOFTIRQ, "HI" }, { TIMER_SOFTIRQ, "TIMER" }, { NET_TX_SOFTIRQ, 
"NET_TX" }, { NET_RX_SOFTIRQ, "NET_RX" }, { BLOCK_SOFTIRQ, "BLOCK" }, { 
BLOCK_IOPOLL_SOFTIRQ, "BLOCK_IOPOLL" }, { TASKLET_SOFTIRQ, "TASKLET" }, 
{ SCHED_SOFTIRQ, "SCHED" }, { HRTIMER_SOFTIRQ, "HRTIMER" }, { 
RCU_SOFTIRQ, "RCU" })


I would like to programmatically extract the action string. 'perf 
script' prints the samples fine which suggests libtraceevent extracts 
the information somehow.

Can you provide a suggestion -- something along the lines of 
perf_evsel__intval() or perf_evsel__rawptr()?

Thanks,
David
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