How to debug Linux kernel using QEMU?

How to debug Linux kernel using QEMU?
1. Install QEMU and install a QEMU VM, the Linux on VM is the one being debugged.
2. Enable some debug configurations, then recompile the kernel. The debugging configurations is described on LDD3 (Linux device driver), chapter 4.
3. Start QEMU VM, use –S argument. It means the VM will be suspended when start.
4. Click on the window of the QEMU VM, press ctrl+alt+2 to switch to QEMU monitor, then type: gdbserver 1234. This will start gdbserver built in QEMU and it listens on the port 1234. Then press “c” to “continue”. Then press alt+ctrl+1 to switch back to OS console.
5. Start a GDB on the host. To get the symbols of the linux kernel, put the source files of the compiled kernel on the same path on the host. Use “gdb vmlinux” to start gdb. Note the vmlinux is an uncompressed file and its size is about 30MB. If it is too small, it may not have necessary debug symbols.
6. In gdb command line, type: “target remote localhost:1234”. This 1234 is the port number used in the gdbserver in step 4.
7. Press “enter”, then the VM should be stopped, and gdb will display some source files, telling where the current function is.
8. To setup a breakpoint, use “b xxx” in gdb, then press “c” to continue.