Building Heads

Heads is supposed to be a reproducible build since v0.1.0 since it achieved this goal. Unfortunately, things broke since release 0.2.1, since some host tools and paths are now bleeding into the final ROM. An alternative build system is being proposed here, with it’s own issues. More research and development needs to be done to bring Heads to be reproducible again, with some additional thinking on reproducibility. Reproducible builds mean that you are supposed to get the same bit by bit output for the same commit. When this idea is confronted to time and inclusion of upstream code which also change and do not necessarily follow guidelines for reproducibility, things are more complicated then it seems. You can try to build 0.2.1 for yourself today to see that it simply doesn’t build anymore to get an idea of some of the problems of such concept if things care not carefully thought forward to be future proof, and get into reproducible build milestone to see current issues that need to be addressed. If you have redroducible build kung fu, please help.

The downside of the reproducibility goal is that the initial build can take a very long time as it downloads and builds all of the its dependencies. One issue right now is that it builds not just one, but two cross compilers and as a result takes about 45 minutes. Luckily subsequent builds only take about 30 seconds to produce a full coreboot and Linux ROM image, but that first ones a doozy…

Heads builds will eventiually be fully reproducible again on any Linux-ish system (OSX build is not supported). If you don’t get the same hashes as reported on the release page, please search/file an issue with the reproducible build milestone.

With a vanilla Debian 11/12 or Ubuntu 20.04/23.04 install, such as a digitalocean droplet, you need to first install some support tools. This takes a short while, so get a cup of coffee and install host build requirements packages as specified by apt calls here

Clone the tree:

git clone https://github.com/osresearch/heads
cd heads

Builds of Heads should be reproducible unless issues are currently known, see Heads milestone #1 for more detail, which means that Heads will build in the exact same way on different computers. Because of this, as a user, you can guarantee that Heads has built correctly and has not been tampered with.

However, this also means that the first time you build Heads it must first build the compilers that it will use to build itself. If that seems complicated, don’t worry. The result is that the first build of Heads will take about an hour to complete. After the first build, building Heads will take less than a minute.

Useful targets, stored under the boards directory of the git tree.

Generic

Generally, everything that is needed to flash the SPI flash of a board is a single rom generated through make BOARD=$BOARD commands, where $BOARD is the name of the board that can be found under board directory of the git downloaded tree. You can do the build verbose by doing make BOARD=$BOARD V=1

Make Heads for another board (XXX should be the name of your board in ./boards and YY the number of CPUs you want to build with):

 make BOARD=XXX CPUS=YY

The resulting rom file for a x86 board will be either ./build/x86/XXX/XXX.rom or ./build/x86/XXX/heads-XXX-vYYYY-gZZZZZZZ.rom (XXX should be the name of your board in ./boards, vYYYY the pinned Heads version and ZZZZZZ the commit id from which your build comes from).

Please continue to the corresponding flashing guide for your device.

More options and detail about Heads modules under Makefile