✎ soc:2008:stefanha:journal:week5

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====== Stefan Hajnoczi: GDB Remote Debugging ======

===== Week 5 =====

**Milestones:**
  * [b44] Tested and clean for mainline review.
  * [bzImage] Fix Lilo stack clobber in prefix.

==== Mon Jun 23 ====
Git commit: [[http://git.etherboot.org/?p=people/stefanha/gpxe.git;a=commit;h=c325ae71ae6ad22442179ddaee7d35017075a29e|[bzImage] Place our own stack to prevent clobbering]]

**Lilo bzImage problem identified**.  Lilo cannot boot ''gpxe.lkrn'' images.  This happens because Lilo places gPXE's stack into the BIOS free memory area.  gPXE uses the free memory area when decompressing and loading itself into memory.

This means that the stack is overwritten during decompression and the machine triple-faults.  I tested this by hardcoding the stack pointer to the value GRUB assigns; this results in a clean boot.

A solution was suggested by mcb30 and is already implemented by some of the other prefixes: set our own stack below 0000:7c00.

**I am continuing work on the b44 driver**.  RX and TX are working but there is lots of cleanup and error handling left.

Next steps:
  * [b44] Handle errors.
  * [b44] Handle link status changes.
  * [b44] Cleanup & testing.
  * [bzImage] Implement a fix for the Lilo stack clobbering problem in prefix.
  * [GDB] 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.
  * [GDB] Real-mode remote debugging.

Trace: • week4 • week3 • week2 • week11 • week7 • week11 • week2 • week3 • week4 • week1 • week5 • week10 • week2 • week4 • week8 • week1 • week3 • week1