Kernel debugging

using qemu

The next "qemu script" example was shamelessly plundered from this course. Keep an eye in the part that says -serial ...

#! /bin/bash

# Fix the paths if necessary
HDA="-drive file=lkp-arch-old.img,format=raw"
HDB="-drive file=myhome.img,format=raw"
SHARED="./share"
KERNEL=kgdbImage

if [ -z ${KDB} ]; then
    CMDLINE='root=/dev/sda1 rw console=ttyS0 kgdboc=ttyS1'
else
    CMDLINE='root=/dev/sda1 rw console=ttyS0 kgdboc=ttyS1 kgdbwait'
fi

FLAGS="--enable-kvm "
VIRTFS+=" --virtfs local,path=${SHARED},mount_tag=share,security_model=passthrough,id=share "

exec qemu-system-x86_64 ${FLAGS} \
     ${HDA} ${HDB} \
     ${VIRTFS} \
     -net user -net nic \
     -serial mon:stdio -serial tcp::1234,server,nowait \
     -boot c -m 1G \
     -kernel "${KERNEL}" \
     -append "${CMDLINE}" # -nographic
#     -initrd "./myinitramfs.cpio.gz"

Once you have your qemu vm running, you need to execute the vmlinux file with gdb. In order to "connect" to the serial port, you use target remote ...

target remote udp:host:port
target remote udp:[host]:port
target remote udp4:host:port
target remote udp6:[host]:port

After this, you could use gdb as usual