tools/stacksnoop.py

#!/usr/bin/python
#
# stacksnoop    Trace a kernel function and print all kernel stack traces.
#               For Linux, uses BCC, eBPF, and currently x86_64 only. Inline C.
#
# USAGE: stacksnoop [-h] [-p PID] [-s] [-v] function
#
# The current implementation uses an unrolled loop for x86_64, and was written
# as a proof of concept. This implementation should be replaced in the future
# with an appropriate bpf_ call, when available.
#
# The stack depth is limited to 10 (+1 for the current instruction pointer).
# This could be tunable in a future version.
#
# Copyright 2016 Netflix, Inc.
# Licensed under the Apache License, Version 2.0 (the "License")
#
# 12-Jan-2016   Brendan Gregg   Created this.

from __future__ import print_function
from bcc import BPF
import argparse
import re

# arguments
examples = """examples:
    ./stacksnoop ext4_sync_fs    # print kernel stack traces for ext4_sync_fs
    ./stacksnoop -s ext4_sync_fs    # ... also show symbol offsets
    ./stacksnoop -v ext4_sync_fs    # ... show extra columns
    ./stacksnoop -p 185 ext4_sync_fs    # ... only when PID 185 is on-CPU
"""
parser = argparse.ArgumentParser(
    description="Trace and print kernel stack traces for a kernel function",
    formatter_class=argparse.RawDescriptionHelpFormatter,
    epilog=examples)
parser.add_argument("-p", "--pid",
    help="trace this PID only")
parser.add_argument("-s", "--offset", action="store_true",
    help="show address offsets")
parser.add_argument("-v", "--verbose", action="store_true",
    help="print more fields")
parser.add_argument("function",
    help="kernel function name")
args = parser.parse_args()
function = args.function
offset = args.offset
verbose = args.verbose
debug = 0

# define BPF program
bpf_text = """
#include <uapi/linux/ptrace.h>

BPF_STACK_TRACE(stack_traces, 128)

void trace_stack(struct pt_regs *ctx) {
    FILTER
    int stack_id = stack_traces.get_stackid(ctx, BPF_F_REUSE_STACKID);
    if (stack_id >= 0)
        bpf_trace_printk("stack_id=%d\\n", stack_id);
}
"""
if args.pid:
    bpf_text = bpf_text.replace('FILTER',
        ('u32 pid; pid = bpf_get_current_pid_tgid(); ' +
        'if (pid != %s) { return; }') % (args.pid))
else:
    bpf_text = bpf_text.replace('FILTER', '')
if debug:
    print(bpf_text)

# initialize BPF
b = BPF(text=bpf_text)
b.attach_kprobe(event=function, fn_name="trace_stack")
matched = b.num_open_kprobes()
if matched == 0:
    print("Function \"%s\" not found. Exiting." % function)
    exit()

stack_traces = b.get_table("stack_traces")
msg_regexp = re.compile("stack_id=(\d+)")

# header
if verbose:
    print("%-18s %-12s %-6s %-3s %s" % ("TIME(s)", "COMM", "PID", "CPU", "SYSCALL"))
else:
    print("%-18s %s" % ("TIME(s)", "SYSCALL"))

# format output
while 1:
    (task, pid, cpu, flags, ts, msg) = b.trace_fields()
    m = msg_regexp.match(msg)
    if m:
        if verbose:
            print("%-18.9f %-12.12s %-6d %-3d %s" % (ts, task, pid, cpu, function))
        else:
            print("%-18.9f %s" % (ts, function))

        stack_id = int(m.group(1))
        for addr in stack_traces.walk(stack_id):
            sym = b.ksymaddr(addr) if offset else b.ksym(addr)
            print("\t%016x %s" % (addr, sym))

        print()