Replicant

h1. Toolchain

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Development efforts to get rid of prebuilt binaries in the Replicant source code are tracked on this page. Prebuilts usually belong to the toolchain, but they can also be found in other parts of the source code. Most of them reside in the @prebuilts@ directory.

h2. Goals

These binaries are committed to AOSP git repos and in most cases, it is poorly documented, how they can be rebuilt, or the documentation is outdated. Compiler rebuild scripts rely on the prebuilt compilers to build the compilers. It is possible that non-free software was used to build the prebuilts (e.g. Google-internal Java compiler). To keep the build trustworthy, we need to make sure, that as little prebuilts as possible are used.

The focus should be on prebuilts that run on the build machine, so basically all prebuilts that belong to the toolchain. We first need to make sure that the toolchain can be trusted by developers and users that build Replicant from source. Then we can focus on binaries that only run on the target devices.

Only building an image for a device needs to work for now. Making e.g. the SDK build target work is a lot more challenging as it depends on a lot more prebuilts.

h2. Strategy

Building as much from source as possible is one strategy to achieve this. Using packaged versions of the prebuilts that are provided by GNU/Linux distributions is an alternative way to ensure that the binaries can be trusted. If the prebuilts are available as packages, then these should be preferred before a clean build from source is investigated. A clean build means that no prebuilts from the AOSP or LineageOS source code are required.

Working on getting build tools packaged by distributions should also be a goal.

h3. Choosing a main target distribution for building Replicant

Debian currently provides by far the most packages that offer replacements for prebuilts. A lot of tools were only packaged for Debian Stretch, so they aren't yet available in most Debian-based distributions. The packages are DFSG-compliant and in accordance to the GNU FSDG.

Debian has their own team that is dedicated to packaging Android tools, the "Debian Android Tools team":https://wiki.debian.org/AndroidTools. We are cooperating with them.

For these reasons, it makes sense to primarily work with Debian Stretch as build system. Requiring certain packages, that are only available in Debian Stretch, breaks the build for other distributions for now. This is a setback we need to accept before packages become available in more distributions. #1787 tries to find a temporary solution to make Replicant buildable on other distributions without relying on untrustworthy prebuilts again.

h2. Already done

Below is a (likely incomplete) overview of the work that has already been done.

h3. Compilers

h3. Manifest

h3. $PATH

No prebuilt binary should be in @$PATH@, so one can be sure that no prebuilt binary is run when executing commands in shell that has environment variables from  @envsetup.sh@ or @lunch@. Only @prebuilts/devtools/tools@ is still part of @$PATH@, but the repo is not fetched by default. However, it is fully clear if prebuilts get copied to @out/host/linux-x86/bin@.

h2. TODO

See "open issues in the build system category":/projects/replicant/issues?set_filter=1&f[]=status_id&op[status_id]=o&f[]=category_id&op[category_id]=%3D&v[category_id][]=153&f[]=&c[]=tracker&c[]=status&c[]=priority&c[]=subject&c[]=assigned_to&c[]=updated_on&c[]=category&c[]=cf_21&group_by=.

More tasks are listed below.

h3. NDK

The Android ARM cross-compiler build uses the sysroot from @prebuilts/ndk/current/platforms/android-21/arch-arm@. The compiler needs to be bootstrapped with proper 1st and 2nd stage compilers so it doesn't rely on the sysroot from the NDK.

Some Makefiles in @build@ reference binaries from @prebuilts/ndk@. It needs to be checked if they are used during an image build and if so whether they can be replaced.

h3. SDK

There are still prebuilt libraries and target APIs in @prebuilts/sdk@. It needs to be investigated which of the libraries are needed to build an image and if the needed ones are already packaged by Debian. It is probably too much work to replace the different target API jar files, so we have to wait until they are packaged by Debian.

h3. Prebuilts in other places

Same as above. It needs to be checked if they are used during an image build and if they can be replaced.

h3. @repo@

Get the @repo@ tool back into the main repository of Debian. It is currently in the contrib repo due to "bug #855846":https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=%23855846. A substantial patch is needed, which should remove the self-updating part of @repo@ or make it optional.