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====== Stefan Hajnoczi: GDB Remote Debugging ====== ===== Week 3 ===== **Milestones:** * GDB remote debugging over UDP. * Hardware watchpoint support for trapping read/write/execute on memory. ==== Mon Jun 9 ==== I had a refreshing weekend with only a little bit of Etherboot hacking on Saturday. The weather was excellent and I was able to recharge batteries a bit :-). The past two weeks of Summer of Code have been an excellent experience. I've had the chance to look behind the scenes of Etherboot and to pitch in and help out. My current focus is on GDB remote debugging over UDP. I think this feature will be very useful since it let's you debug gPXE without using a serial cable. It opens the door to letting developers analyze errors over the internet without having to reproduce them locally from a bug report. I'd really like to see this used in cases where developers do not have hardware on which the error occurs. Today I implemented UDP send and receive without using the network stack. This means hand-crafting Ethernet, IP, UDP packets and parsing them. One detail I hadn't though of is that ARP reply code is also necessary to advertise gPXE's MAC/IP addresses. GDB can already talk to gPXE via UDP. The conversation does not go well though. It deadlocks after a few exchanges and before handshaking is complete when neither side wants to say any more. I think this is either because of bugs in my UDP send/receive code or due to flow control issues when using UDP. The GDB protocol is sensitive to packet ordering. I have tried to implement the GDB protocol in a robust way, so I suspect the error lies in the UDP code. Tomorrow I'll look into this more. Meanwhile, here is a screenshot from [[http://www.wireshark.org/|Wireshark]]: {{:soc:2008:stefanha:journal:udp.png|GDB and gPXE trying to talk to each other over UDP.}} Next steps: * Implement UDP transport. * Implement hardware watchpoint support using debug registers. * NULL pointer bug guard using watchpoint support. * Use screen captures on [[:dev:gdbstub|GDB stub page]].
