There is one bug with this method. You CANNOT stepi through the jmp that lands in 64-bit code as this will cause VMware to crash; you can however continue to a breakpoint on the other side. I have not tested a breakpoint in the higher-half yet as I haven't had time.
If someone could test that I will update this post.
I'll be using the xomb bare bones kernel as an example although I have modified mine to be assembly only; essentially I removed the call to kmain and only link boot.S and load.S.
The most helpful documentation for the boot.S/load.S files is at: XBB From Start to Finish
Tools used:
- Ubuntu 64-bit host 8.10
- Ubuntu 64-bit 8.10 Desktop installation CD image
- VMware Workstation 6.5
- GParted Live CD 0.4.3-2 image
- apt-get install build-essential git-svn git-gui gcc-multilib ddd
- create a 64-bit virtual machine with VMware
- partition the disk using GParted
- install GRUB on the disk image with the Ubuntu install CD
- add debugStub32/64 and hideBreakpoints to the vmx configuration file
- git clone git://github.com/xomboverlord/xomb-bare-bones.git
- modify load.S to not call kmain and linker.ld to remove paths
VMware
- Machine: I will install the operating system later, OS Other 64-bit, 1024MB memory, 12GB IDE hard disk single file
- Set the Virtual CD to the GParted Live CD image
- Add the following lines to the virtual machine *.vmx file:
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bios.bootDelay = "3000" debugStub.hideBreakpoints = "TRUE" # allows gdb breakpoints to work debugStub.listen.guest32 = "TRUE" # (gdb) target remote localhost:8832 debugStub.listen.guest64 = "TRUE" # (gdb) target remote localhost:8864 #debugStub.listen.guest32.remote = "TRUE" # for debugging from another machine #debugStub.listen.guest64.remote = "TRUE" # for debugging from another machine #monitor.debugOnStartGuest32 = "TRUE" # This will halt the VM at the very first instruction at 0xFFFF0, you could set the next breakpoint to break *0x7c00 to break when the bootloader is loaded by the BIOS
- Partition the 12GB into: 100MB label=boot ext3, 9.90GB label=root ext3, 2.0GB swap
- Set the Virtual CD to the Ubuntu CD image
- When VMware boots, hit ESC when the BIOS appears to get the boot menu and select CD-ROM Drive
- Boot into the 'Try Ubuntu' portion
- Perform the following commands to install GRUB on the disk:
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ls -l /dev/disk/by-label # list drive e.g. boot -> ../../sda1 sudo fdisk -l # if you did not assign a label sudo mount /dev/sda1 /mnt/ sudo grub-install --root-directory=/mnt/ /dev/sda sudo gedit /mnt/boot/grub/device.map # change (hd0) /dev/sda to (hd0) /dev/hda
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/* Debug 32-bit boot code */
# Boot to GRUB shell
# run ddd, make sure the View | Machine Code Window and View | Command Tool are available
set architecture i386
target remote localhost:8832
# Break where the kernel will be loaded by GRUB
break *0x100000
continue
/* transition to 64-bit */
# before jumping to 64-bit code gdb needs to be placed into x86-64 mode and the target switched to the debugStub64 remote
# first, set a breakpoint at the linear address in 64-bit space your kernel will be jumping into, this can be seen in the 32-bit disassembly
break *0x118000
continue
# gdb will hang as the debugStub32 stops responding. Hit Ctrl-C twice or click Interrupt twice in the ddd Command Tool to revive the (gdb) prompt
# The vmware.log will contain something like: Mar 27 19:43:33.359: vcpu-0| Waiting for Guest 64-bit debugger to connect!
set architecture i386:x86-64
target remote localhost:8864
# we should now be in 64-bit space at the breakpoint we set earlier.
# when the kernel jumps to the higher-half, ddd (gdb) follows along flawlessly
/* Debug 64-bit boot code without transtion from 32-bit */
# Boot to GRUB shell
# in GRUB
kernel /boot/xomb
boot
# in ddd
set architecture i386:x86-64
break *<known address>
target remote localhost:8864
