[Qemu-devel] Failed to set a breakpoint on start_kernel

[Wei Yang]

All

I like qemu very much and know it could debug the kernel.

I tried what I searched on web but couldn't stop at the break point.
Below is what I did.

1. Both host and guest installed the same OS, Fedora16 x86_64.

2. Compile the qemu with
    ./configure --target-list=x86_64-softmmu --enable-kvm
--enable-debug-tcg --enable-debug --enable-trace-backend=simple

3. With this command I can boot up my guest.
    ./../qemu/x86_64-softmmu/qemu-system-x86_64 -enable-kvm -smp 4 -m
1024  -boot dc fedora16.img -monitor stdio

4. I git clone the kernel source in the guest and make a new kernel and initrd.
    I start the guest with this new kernel successfully

5. I copy out the initrd.img and the .config of kernel to host.
compile the kernel on host.
    the kernel source code is identical on host and gueset,

6. I start the guest with the kernel and initrd on host
    ./../qemu/x86_64-softmmu/qemu-system-x86_64 -enable-kvm -smp 4 -m
1024  -boot dc fedora16.img -monitor stdio -kernel
~/git/linux-yinghai/arch/x86_64/boot/bzImage -initrd
~/git/debug/initramfs-3.0.0.img -append
"root=/dev/mapper/vg_wizard-lv_root ro rd.lvm.lv=vg_wizard/lv_root
rd.md=0 rd.lvm.lv=vg_wizard/lv_swap"

    This works fine.

7. Then I start the guest with gdbstub option
    ./../qemu/x86_64-softmmu/qemu-system-x86_64 -enable-kvm -smp 4 -m
1024  -boot dc fedora16.img -monitor stdio -kernel
/home/ywywyang/git/linux-yinghai/arch/x86_64/boot/bzImage -initrd
/home/ywywyang/git/debug/initramfs-3.0.0.img -append
"root=/dev/mapper/vg_wizard-lv_root ro rd.lvm.lv=vg_wizard/lv_root
rd.md=0 rd.lvm.lv=vg_wizard/lv_swap" -S -gdb tcp::4321

    Then the guest stop at the beginning.

8. Attach the gdb in the kernel source directory
    gdb
    file vmlinux
    target remote localhost:4321
    b start_kernel
    c

   Then the guest will run very happily....

    Also use the "info b " could show the break point is set.

Which step I made a mistake?


-- 
Wei Yang
Help You, Help Me