joelagnel

#!/bin/sh

# Check if at least one numeric arg is passed
if [ $# -eq 0 ]
then
    echo "Usage: $0 <seconds>"
    exit 1
fi

# Read and discard input for 1 second

joelagnel

#!/bin/sh
# Save this file as "init" in the root of your CPIO archive,
# and chmod +x it. This will chroot into an HDD if one is
# available. Or it will just give a prompt.

mkdir -p /proc /sys /d /pstore /dev
mount -t proc none /proc
mount -t sysfs none /sys
mount -t debugfs none /d
mount -t debugfs none /sys/kernel/debug/

joelagnel

#!/bin/bash
# Author: Joel Fernandes <joel@joelfernandes.org>
#
# Usage, run-qemu		: Runs with busybox chrooting into a debian qemu.img 
# run-qemu --rt			: Set all Qemu vCPU threads as RT and pin them to different CPUs.
# run-qemu --rcu		: Run qemu with rcutorture boot parameters
#
# run-qemu --cpio 		: Runs only with busy-box initramfs (no chrooting)
# run-qemu --debian		: Boot into a debian rootfs (see end of this file for how to build debian images)
# If neither --cpio nor --debian is passed, then it will try to chroot into a qemu.img file.

joelagnel

#!/usr/bin/python3
# Run for tracing:
# With full screen video playing on device, run:
# trace-cmd record -e timer:hrtimer_start -R stacktrace -e hrtimer_cancel -e timer:hrtimer_expire_entry -- sleep 5
# trace-cmd report > trace.txt
# Pass the trace to this script.
# The script will produce a filter_trace.txt which only shows hrtimer events that actually fired and
# did not get canceled.
# The script will also output the top-most frequent stacks that queued a timer.

joelagnel

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/kthread.h>
#include <linux/delay.h>
#include <linux/moduleparam.h>
#include <linux/list.h>

joelagnel

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/slab.h>

static char *crash_type = "null";
module_param(crash_type, charp, S_IRUGO | S_IWUSR);

MODULE_LICENSE("GPL");

joelagnel

#!/bin/bash

function cleanup {
    echo "Exiting script, killing child processes..."
    kill $pid1 $pid2
    # Remove the cgroups
    cgdelete -g cpu:group1
    cgdelete -g cpu:group2
    exit 1
}

joelagnel

#!/bin/bash

function cleanup {
    echo "Exiting script, killing child processes..."
    kill $pid1 $pid2
    exit 1
}

trap cleanup EXIT

joelagnel

Kernel Debug Tricks of the trade

NOTE: Updated on 3/11/2023.

Introduction

Debugging the kernel is a difficult task. Thankfully there are quite a few built-in kernel debugging tools and techniques that help one quickly identify the source and/or the cause of an issue.

Enable debug information

joelagnel

// Author: Steven Rostedt
//
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <stdarg.h>
#include <errno.h>
#include <time.h>