Daniel Verkamp: COMBOOT Support

• After a conversation with mcb30 last Thursday on how to fix the problems with COM32 stack overwrites during image loading, I've implemented his suggestions. This resulted in a 3-day debugging marathon until I switched to a simpler test case and just single stepped through the entire image execution process… and finally noticed (thanks to the Intel-syntax Bochs debugger) that I had written a constant as 12 instead of $12 (AT&T syntax strikes again ). But the upshot of all this is that COM32 programs using “Run kernel image” work totally correctly now, without any hack to limit the stack size, and I can say without reservation that menu.c32 is working perfectly fine now (given the configuration filename via the command line); it can load itself numerous times (until there is no more memory left to load the image again) as well as other image types without any problems now. I plan to start doing further testing on real hardware with various booting scenarios now, but so far, everything looks good.

• Added a jmp to self-modifying intcall code to avoid problems on 486 (makes execution in qemu much faster too) 3d6bd95bcb0919c4c14df0a1bce3641388f6d88d

Since menu.c32 is working well now, here is a sample SYSLINUX menu I am using to test (http://10.0.0.11 is a web server):

default menu.c32
prompt 0
menu title gPXE COMBOOT menu test

timeout 600

label tomsrtbt
  menu label tomsrtbt
  menu default
  kernel http://10.0.0.11/~daniel/gpxe/gtest/bz2bzImage
  append initrd=http://10.0.0.11/~daniel/gpxe/gtest/initrd.bz2 root=100

label gtest
  menu label tomsrtbt via gtest.gpxe
  kernel http://10.0.0.11/~daniel/gpxe/gtest.gpxe

label tube
  menu label tube
  kernel http://10.0.0.11/~daniel/gpxe/TUBE.COM

• Had a bit of fun playing with xl0's newly-ported Lua COM32 module ( SYSLINUX mailing list thread ); it worked fine without any modifications (although I haven't tested much). You can see my obvious incompetence at Lua (the function is an example from Programming in Lua):