1#!/bin/bash
  2# SPDX-License-Identifier: GPL-2.0
  3#
  4# Here's how to use this:
  5#
  6# This script is used to help find functions that are being traced by function
  7# tracer or function graph tracing that causes the machine to reboot, hang, or
  8# crash. Here's the steps to take.
  9#
 10# First, determine if function tracing is working with a single function:
 11#
 12#   (note, if this is a problem with function_graph tracing, then simply
 13#    replace "function" with "function_graph" in the following steps).
 14#
 15#  # cd /sys/kernel/debug/tracing
 16#  # echo schedule > set_ftrace_filter
 17#  # echo function > current_tracer
 18#
 19# If this works, then we know that something is being traced that shouldn't be.
 20#
 21#  # echo nop > current_tracer
 22#
 23#  # cat available_filter_functions > ~/full-file
 24#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
 25#  # cat ~/test-file > set_ftrace_filter
 26#
 27# *** Note *** this will take several minutes. Setting multiple functions is
 28# an O(n^2) operation, and we are dealing with thousands of functions. So go
 29# have  coffee, talk with your coworkers, read facebook. And eventually, this
 30# operation will end.
 31#
 32#  # echo function > current_tracer
 33#
 34# If it crashes, we know that ~/test-file has a bad function.
 35#
 36#   Reboot back to test kernel.
 37#
 38#     # cd /sys/kernel/debug/tracing
 39#     # mv ~/test-file ~/full-file
 40#
 41# If it didn't crash.
 42#
 43#     # echo nop > current_tracer
 44#     # mv ~/non-test-file ~/full-file
 45#
 46# Get rid of the other test file from previous run (or save them off somewhere).
 47#  # rm -f ~/test-file ~/non-test-file
 48#
 49# And start again:
 50#
 51#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
 52#
 53# The good thing is, because this cuts the number of functions in ~/test-file
 54# by half, the cat of it into set_ftrace_filter takes half as long each
 55# iteration, so don't talk so much at the water cooler the second time.
 56#
 57# Eventually, if you did this correctly, you will get down to the problem
 58# function, and all we need to do is to notrace it.
 59#
 60# The way to figure out if the problem function is bad, just do:
 61#
 62#  # echo <problem-function> > set_ftrace_notrace
 63#  # echo > set_ftrace_filter
 64#  # echo function > current_tracer
 65#
 66# And if it doesn't crash, we are done.
 67#
 68# If it does crash, do this again (there's more than one problem function)
 69# but you need to echo the problem function(s) into set_ftrace_notrace before
 70# enabling function tracing in the above steps. Or if you can compile the
 71# kernel, annotate the problem functions with "notrace" and start again.
 72#
 73
 74
 75if [ $# -ne 3 ]; then
 76  echo 'usage: ftrace-bisect full-file test-file  non-test-file'
 77  exit
 78fi
 79
 80full=$1
 81test=$2
 82nontest=$3
 83
 84x=`cat $full | wc -l`
 85if [ $x -eq 1 ]; then
 86	echo "There's only one function left, must be the bad one"
 87	cat $full
 88	exit 0
 89fi
 90
 91let x=$x/2
 92let y=$x+1
 93
 94if [ ! -f $full ]; then
 95	echo "$full does not exist"
 96	exit 1
 97fi
 98
 99if [ -f $test ]; then
100	echo -n "$test exists, delete it? [y/N]"
101	read a
102	if [ "$a" != "y" -a "$a" != "Y" ]; then
103		exit 1
104	fi
105fi
106
107if [ -f $nontest ]; then
108	echo -n "$nontest exists, delete it? [y/N]"
109	read a
110	if [ "$a" != "y" -a "$a" != "Y" ]; then
111		exit 1
112	fi
113fi
114
115sed -ne "1,${x}p" $full > $test
116sed -ne "$y,\$p" $full > $nontest