Debugging Linux Kernel using QEMU

create-rootdisk-kernel-dbg

#!/bin/bash
 
# Copyright (C) Tejas Wanjari (twanjari@andrew.cmu.edu)
 
#                              GNU/GPL
#                              -------
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
 
# Fill in the macros
# ------------------------------------------------------------------------
 
DEBIAN_DISTRO="wheezy"
FS="ext4"
ARCH="i386"
MOUNT_POINT="/mnt/wheezy/"
IMG="$HOME/$DEBIAN_DISTRO-$ARCH.img"
 
# ------------------------------------------------------------------------
 
# Make sure only root can run our script
if [ "$(id -u)" != "0" ]
then
   echo "This script must be run as root" 1>&2
   exit 1
fi
 
# Following binaries are mandetory
BINS="dd mount umount mkfs.$FS debootstrap"
for i in $BINS
do
        which $i > /dev/null  && continue  || \
                { echo "$i command not found."; exit 1; }
done
 
# Check if the disk image is already mounted
mountpoint -q $MOUNT_POINT && umount -f $MOUNT_POINT
 
# Create raw disk image [size = bs * count]
echo -e "\nCreating disk image $IMG"
dd if=/dev/zero of=$IMG bs=1K count=1M || exit 1
du -h $IMG
 
# Format the hda (ext3 is perferred -- better for large no. of small files
# than ext2, and smaller footprint than ext4 since there is no journaling
# overhead)
echo -e "\nFormatting $IMG"
mkfs.$FS -F $IMG || exit 1
file $IMG
 
# Mount the disk image
echo -e "\nCreating mount-point $MOUNT_POINT"
mkdir -p $MOUNT_POINT
echo "Mounting $IMG, mount-point: $MOUNT_POINT"
mount -o loop $IMG $MOUNT_POINT || exit 1
 
# Bootstrapping the rootfs
echo -e "\nCreating the root file system"
echo "This may take a while..."
debootstrap --arch=$ARCH $DEBIAN_DISTRO $MOUNT_POINT \
     "http://ftp.us.debian.org/debian" || exit 1
echo "======== rootfs created ========"
 
#Create serial port and sda in /dev of the image
mknod $MOUNT_POINT/dev/ttyS0 c 80 10
mknod $MOUNT_POINT/dev/sda1 c 70 10
 
# Unmount
echo -e "\nCleaning up"
umount $MOUNT_POINT
rm -rf $MOUNT_POINT
 
# hda ready
echo -e "\nhda: $IMG ready."

kern-dgb.info

#!/bin/bash

# -S  Do not start CPU at startup (you must type 'c' in the monitor).
# -s  Shorthand for -gdb tcp::1234, i.e. open a gdbserver on TCP port 1234.

# No-GUI debugging
qemu -kernel bzImage -append "root=/dev/sda console=ttyS0" -m 2G -hda wheezy.img -serial stdio -nographic -nodefaults -s -S

# QEMU opens GUI term to debug
qemu -kernel bzImage -append "root=/dev/sda console=tty0" -m 2G -hda wheezy.img -s -S

# Inside gdb in other term
gdb bzImage
(gdb) target remote localhost:1234