Daniel Verkamp: COMBOOT Support

My goal is to add support for booting COMBOOT and COMBOOT32 images in gPXE.

This includes:

• Adding a new image type for COMBOOT
• Implementing the COMBOOT API (including the PXE portions) and setting up the IDT to point to these implementations

I will implement COMBOOT API support in gPXE. This will require implementing the COMBOOT API functions within gPXE and hooking up the interrupt table (or the protected-mode helper, for COM32) to call the gPXE implementation, setting up real or protected mode depending on whether the image is 16- or 32-bit, then loading and executing the COMBOOT image.

For initial testing, the most basic part of the API will be implemented (INT 20h, terminate program) in order to test the loading and execution of COMBOOT executables. Once this is working (both in 16- and 32-bit mode), the rest of the SYSLINUX API that makes sense in the context of gPXE will be implemented, including the PXELINUX-only functions.

16-bit COMBOOT executables will require switching to real mode and setting up the interrupt table appropriately.

COM32 executables will additionally require protected-mode setup and the provision of a protected-mode callback to call COMBOOT and BIOS functions.

• Implement bare minimum COMBOOT API and COMBOOT loading (at the very latest, this should be done by mid-summer, but most likely should be done in a few weeks)
• Improve COM32 helper function to call BIOS functions
• Implement the rest of the COMBOOT API, as time permits