linux-kernel - Re: perf probe and structs

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Date:	Fri, 12 Jun 2015 19:58:02 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
CC:	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: perf probe and structs

On 6/12/15 12:27 PM, Arnaldo Carvalho de Melo wrote:
> Alexei, is this already possible with eBPF?
> I want to decode that attr_uptr thing :-)

yes, it's already possible :)

Here is working example from our experimental c+python thingy:
#!/usr/bin/env python

from bpf import BPF
from subprocess import call

prog = """
#include <uapi/linux/ptrace.h>
#include <uapi/linux/perf_event.h>
int hello(struct pt_regs *ctx)
{
   struct perf_event_attr attr = {};
   bpf_probe_read(&attr, sizeof(attr), (void *) ctx->di);
   char fmt[] = "type %x size %d config %d\\n";
   bpf_trace_printk(fmt, sizeof(fmt), attr.type, attr.size, attr.config);
   return 0;
}
"""
b = BPF(text=prog)
fn = b.load_func("hello", BPF.KPROBE)
BPF.attach_kprobe(fn, "SYSC_perf_event_open")
try:
     call(["cat", "/sys/kernel/debug/tracing/trace_pipe"])
except KeyboardInterrupt:
     pass

running above gives me output:
# ./example.py
       perf_4.1.0-5544  [001] d.h3  3818.231428: : type 1 size 0 config 0
       perf_4.1.0-5544  [001] d.h3  3818.231494: : type 0 size 112 config 0
       perf_4.1.0-5544  [001] d.h3  3818.231530: : type 0 size 112 config 0
       perf_4.1.0-5544  [001] d.h3  3818.231554: : type 0 size 112 config 0
       perf_4.1.0-5544  [001] d.h3  3818.231564: : type 0 size 112 config 0

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