(Experimental) building gPXE for coreboot

Update: March 4, 2009

make versions more explicit
fix broken links
add contact info (at bottom)

Building gPXE For Coreboot

Please find below some notes on how I put together an experimental gPXE payload for coreboot. I'm sure there are other ways to accomplish the result I wanted, but these procedures worked for me.

These notes only cover the building of the gPXE coreboot payload ELF. After you have the ELF you may try putting it into your coreboot ROM.

Warning! Do not use these notes to create and use a gPXE coreboot payload unless you know what you are doing with coreboot, and have access to hardware-based re-flashing tools. These notes are provided as a courtesy. You are responsible for your own results, etc, blah blah blah.

Approach

download libpayload
modify libpayload to produce an extra library with some alternate symbol names to avoid conflict with gPXE symbols
build libpayload
download gPXE snapshot
modify gPXE so 16-bit code need not be compiled
customize gPXE configuration
add a libpayload-based console to gPXE
add a libpayload-based memory map to gPXE
modify gPXE's ELF support to actually execute the downloaded ELF image
build gPXE's blib.a archive
trim out the 16-bit stuff from blib.a
make a small C-start so coreboot starts up gPXE okay
link a coreboot-friendly gPXE ELF

Getting libpayload

$ svn co svn://coreboot.org/repos/trunk/payloads/libpayload -r3473

Add gPXE-friendly library target to libpayload

$ wget http://www.whiterocker.com/gpxe/libpayload-lplconsole.patch
$ patch -p0 < libpayload-lplconsole.patch

Build libpayload

$ make -C libpayload menuconfig # make selections, save and exit
$ make -C libpayload

Getting gPXE

$ wget http://kernel.org/pub/software/utils/boot/gpxe/Old/gpxe-0.9.3.tar.bz2
$ tar xjf gpxe-0.9.3.tar.bz2

Patching gPXE to avoid 16-bit code in mandatory object files

$ wget http://www.whiterocker.com/gpxe/no-16bit.patch
$ patch -p0 < no-16bit.patch

Customizing the gPXE configuration

Here gPXE is configured for ELF image support. Most other types cannot be supported in my approach because 16-bit code has been trimmed. Check gpxe-0.9.3/src/config.h for other possible options.

$ wget http://www.whiterocker.com/gpxe/coreboot_config.patch
$ patch -p0 < coreboot_config.patch

Adding a libpayload console to gPXE

$ wget http://www.whiterocker.com/gpxe/coreboot_console.patch
$ patch -p0 < coreboot_console.patch

Making gPXE aware of the coreboot memory map

$ wget http://www.whiterocker.com/gpxe/coreboot_memmap.patch
$ patch -p0 < coreboot_memmap.patch

Coercing gPXE to execute an ELF image

$ wget http://www.whiterocker.com/gpxe/elf-image-exec.patch
$ patch -p0 < elf-image-exec.patch

Making gPXE's blib.a

$ make -C gpxe-0.9.3/src bin/blib.a

Trimming 16-bit stuff from gPXE's blib.a

$ mkdir -p blib
$ cd blib
$ ar xf ../gpxe-0.9.3/src/bin/blib.a
$ rm -f abft.o basemem_packet.o bImageprefix.o bios_console.o biosint.o \
  bios.o bootsector.o bzimage.o comprefix.o dskprefix.o e820mangler.o \
  elf_dprefix.o exeprefix.o gateA20.o gdbsym.o hdprefix.o hidemem.o \
  ibft.o int13.o kpxeprefix.o libkir.o libprefix.o librm.o lkrnprefix.o \
  lmelf_dprefix.o lmelf_prefix.o memmap.o multiboot.o nbi.o nbiprefix.o \
  nullprefix.o pcibios.o pxe_call.o pxe_entry.o pxe_loader.o pxe_preboot.o \
  pxeprefix.o pxe_undi.o romprefix.o stack16.o undiisr.o undiload.o \
  undinet.o undi.o undionly.o undipreload.o elfprefix.o
$ ar q trimmed-gpxe-blib.a *.o
$ cd ..

A small C-start for gPXE under coreboot

$ wget http://www.whiterocker.com/gpxe/gpxe-coreboot-cstart.S
$ gcc -c gpxe-coreboot-cstart.S

Linking the gPXE payload

You will want to choose a specific ethernet controller driver. I show pcnet32 in the example final link below, consult the gPXE sources for others.

$ wget http://www.whiterocker.com/gpxe/gpxe-coreboot-payload.lds

$ ld -N -T gpxe-coreboot-payload.lds \
-u obj_pcnet32 --defsym check_obj_pcnet32=obj_pcnet32 \
-u obj_config --defsym check_obj_config=obj_config \
-u obj_stack --defsym check_obj_stack=obj_stack \
--defsym pci_vendor_id=0x1022 --defsym pci_device_id=0x2000 \
gpxe-coreboot-cstart.o \
libpayload/lib/lplconsole.o \
blib/trimmed-gpxe-blib.a \
-o gpxe-coreboot-payload-debug.elf

$ objcopy -j .data gpxe-coreboot-payload-debug.elf gpxe-coreboot-payload.elf

Contact Info

Chris Kilgour
(technical, mailing list address): techie at this domain