Le samedi 17 mars 2012 à 09:53 +0100, Jan Kiszka a écrit : > On 2012-03-16 03:43, Wei Yang wrote: > > 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? > > Two major issues with this procedure: > > 1. When using kvm, a soft breakpoint (as set by 'b') will inject a trap > instruction into the guest image - which is not yet loaded after the > bios ran. You need to use a hardware breakpoint in this case. > > 2. Due to gdb limitations, you cannot switch between 16/32-bit mode (the > CPU starts in 16 bit) and the 64-bit mode of kernel within the same gdb > session. Therefore: > - let the target run into Linux is active > - attach gdb > - issue "hw start_kernel" > - reboot (e.g. "monitor system_reset") > - you will hit the breakpoint, and gdb will be usable
You can also try my patch : http://patchwork.ozlabs.org/patch/137543/ Laurent
