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Merge pull request #153 from tlaurion/nix_buildstack_corrections
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General build instructions: update documentation since Nix buildstack is now used
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tlaurion authored May 12, 2024
2 parents f29e41a + 9aaa6f5 commit 2e200f9
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41 changes: 6 additions & 35 deletions Installing-and-Configuring/Building-Heads/general.md
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Expand Up @@ -18,42 +18,14 @@ grand_parent: Installing and configuring
</details>
<!-- markdownlint-enable MD033 -->


Building Heads
===

Heads is supposed to be a [reproducible build](https://reproducible-builds.org/)
since [v0.1.0](https://github.com/osresearch/heads/releases/tag/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](https://github.com/osresearch/linux-builder),
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](https://github.com/osresearch/linux-builder/issues/1).
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](https://github.com/osresearch/heads/milestone/1)
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](https://github.com/osresearch/heads/issues/96)).
If you don't get the same hashes as reported on the release page, please
search/file an issue with the [reproducible build milestone](https://github.com/osresearch/heads/milestone/1).

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](https://github.com/osresearch/heads/blob/master/.circleci/config.yml)
With the new Nix build system, building Heads has become more streamlined.

Please refer to the [Building Heads](https://github.com/linuxboot/heads/blob/master/README.md#building-heads) section in the [Heads README](https://github.com/linuxboot/heads/blob/master/README.md) for updated instructions on how to build Heads using the Nix build system's produced docker image reproducibly.

For more information, you can also check out the [pull request #1661](https://github.com/linuxboot/heads/pull/1661) which provides additional details and updates to the build process.

Clone the tree:

Expand All @@ -76,7 +48,6 @@ However, this also means that the first time you build Heads it must first build

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


Generic
---

Expand All @@ -88,7 +59,7 @@ Generally, everything that is needed to flash the SPI flash of a board is a
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):

```Makefile
make BOARD=XXX CPUS=YY
docker run -e DISPLAY=$DISPLAY --network host --rm -ti -v $(pwd):$(pwd) -w $(pwd) tlaurion/heads-dev-env:latest -- make BOARD=XXX CPUS=YY
```

The resulting rom file for a x86 board will be either `./build/x86/XXX/XXX.rom` or
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