2016 May 01 Kernel, Virtualization

Debug kernel by qemu!

Steps:

creates a configuration based on the defaults for your architecture

# make defconfig

define extra configuration if required.

# vim .config      --> edit by yourself
# make menuconfig  --> which can help to add some configuration automatically

enable debug info option

Kernel debugging->Compile the kernel with debug info”

    [*] KGDB: kernel debugging with remote gdb
        Method for KGDB communication (KGDB: On generic serial port (8250)) --->
    [*] KGDB: Thread analysis
    [*] KGDB: Console messages through gdb

compile kernel

# make -j<n>

confirm the result of compile

[root@localhost linux-debug]# pwd
/mnt/extra_disk/osc/linux-debug
[root@localhost linux-debug]# ll arch/x86/boot/bzImage
-rw-r--r-- 1 root root 6414240 Jun 17 17:10 arch/x86/boot/bzImage

start qemu with the compiled kernel

#qemu-system-x86_64 -s -S -kernel /mnt/extra_disk/osc/linux-debug/arch/x86/boot/bzImage -hda linux-0.2.img -append "root=/dev/sda console=ttyS0" -m 512M

Note: -s option makes Qemu listen on port tcp::1234; -S option makes Qemu stop execution until you give the continue command

start gdb in another terminal

# gdb /mnt/extra_disk/osc/linux-debug/arch/x86/boot/vmlinux
(gdb) target remote localhost:1234
Remote debugging using localhost:1234
0x0000000000000000 in irq_stack_union ()
(gdb) b start_kernel
Breakpoint 1 at 0xffffffff81f42c00
(gdb) c
(gdb) list   --> browse the current line's codes

Maybe you’ll met “gdb - Remote ‘g’ packet reply is too long”, Please update gdb from source codes and comment the statments in ‘gdb/remote.c’ like below,

 //if (buf_len > 2 * rsa->sizeof_g_packet)
 //  error (_("Remote 'g' packet reply is too long: %s"), rs->buf);

There is but one secret to sucess—never give up!