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====== Stefan Hajnoczi: GDB Remote Debugging ====== ===== Week 4 ===== **Milestones:** * Get latest GDB stub work into mainline. * Modern bzImage prefix for gPXE. ==== Mon Jun 16 ==== **The ''gdbstub2'' branch is now ready for mainline review**. Diffs against gPXE ''master'' are [[http://etherboot.org/share/stefanha/gdbstub2.diff|here]]. Once it is merged I will update the documentation and encourage others to use GDB. **gPXE needs modern bzImage support so that GRUB, lilo, and SYSLINUX can load it**. This is my next piece of work after the GDB stub. There is already code in etherboot to make a bzImage. The old code doesn't work by default on today's popular bootloaders since the Linux bzImage header it supplies is outdated. I am investigating what needs to be done for GRUB, lilo, SYSLINUX, etherboot, and gPXE to load a gPXE bzImage. ==== Tue Jun 17 ==== **I am trying out bootloaders on ''gpxe.lkrn'' images**. We were afraid that the outdated Linux zImage prefix no longer works with modern bootloaders. Here are results for unmodified gPXE (I have not yet attempted to implement bzImage): * **GRUB** boots ''gpxe.lkrn'' successfully. Here is a script to create a GRUB/gPXE boot floppy: <code> #!/bin/sh set -e dd if=/dev/zero of=grub.img bs=1024 count=1440 losetup /dev/loop0 grub.img mkfs /dev/loop0 mount /dev/loop0 /mnt mkdir -p /mnt/boot/grub cp /boot/grub/stage1 /boot/grub/stage2 /mnt/boot/grub/ cat >/mnt/boot/grub/menu.lst <<EOF title=gPXE root (fd0) kernel /boot/gpxe.lkrn EOF cp bin/gpxe.lkrn /mnt/boot/ umount /mnt grub --device-map=/dev/null <<EOF device (fd0) /dev/loop0 root (fd0) setup (fd0) quit EOF losetup -d /dev/loop0 </code> * **SYSLINUX** boots ''gpxe.lkrn'' successfully. Here is a script to create a boot floppy: <code> #!/bin/sh set -e dd if=/dev/zero of=syslinux.img bs=1024 count=1440 mkfs.msdos syslinux.img mount -o loop syslinux.img /mnt cp bin/gpxe.lkrn /mnt/gpxe.zi cat >/mnt/SYSLINUX.CFG <<EOF default gpxe.zi EOF umount /mnt syslinux syslinux.img </code> * **lilo** boots ''gpxe.lkrn'' unsuccessfully. QEMU stops with a triple-fault. I still need to look into this. Here is a script to create a boot floppy: <code> #!/bin/sh set -e dd if=/dev/zero of=syslinux.img bs=1024 count=1440 losetup /dev/loop0 lilo.img mkfs /dev/loop0 mount /dev/loop0 /mnt mkdir /mnt/etc /mnt/boot cp bin/gpxe.lkrn /mnt/gpxe.zi cat >/mnt/etc/lilo.conf <<EOF boot =/dev/loop0 disk =/dev/loop0 bios =0x00 # 1.44MB disk geometry sectors =18 heads =2 cylinders =80 install =/mnt/boot/boot.b map =/mnt/boot/map backup =/dev/null image =/mnt/gpxe.zi EOF /tmp/lilo/sbin/lilo -C /mnt/etc/lilo.conf umount /mnt losetup -d /dev/loop0 </code> * **gPXE** boots ''gpxe.lkrn'' unsuccessfully since only the newer bzImage and not the old zImage format is supported. Testing was easy: <code> qemu -bootp gpxe.lkrn -tftp bin bin/gpxe.usb </code> * **Etherboot 5.4.3** boots ''gpxe.lkrn'' successfully. I used [[http://freshmeat.net/projects/wraplinux/|wraplinux]] to make an NBI file from ''gpxe.lkrn''. Next steps: * Update [[:dev:gdbstub|GDB stub page]] and screencast when UDP code is merged into mainline. See [[http://grub.enbug.org/DebuggingWithGDB|GRUB GDB wiki page]] for inspiration. * gPXE bzImage support. * Real-mode GDB stub.
