ADR-0002: Wrapped packages run Buildroot's own make

Status: accepted Date: 2026-09-20

Context

Buildroot's package infrastructure (autotools-package, cmake-package, kernel and toolchain packages, hooks, patches, _POST_INSTALL_TARGET_HOOKS) is thousands of lines of make that encode years of accumulated build knowledge. A Buck2 rule set that reimplements it will always trail Buildroot, and a project's own .mk files use all of it.

Decision

The default variant, wrapped, runs make <pkg> inside the Buck2 action, in a scratch output tree seeded with the package's dependencies' outputs and its config slice. Buck2 owns the graph, ordering, parallelism, caching and remote execution; Buildroot owns how a package is built. A native variant replaces selected packages with Buck2 actions that do the work themselves, behind the same target label and artifact format, so the two variants can be mixed per package and compared.

Consequences

• Easier: every Buildroot package works on day one, including Mesa, vendor kernels and Rust host tools; the project's .mk files and hooks run unchanged.
• Easier: the native variant has an oracle. A native package's artifact is compared with the wrapped one (compare-pkg.py).
• Harder: the action is a black box to Buck2. Early cutoff is per package, and the action reads ambient host tools (gcc, perl, rsync) the cache key does not cover. Remote execution therefore needs a pinned worker image; see ADR-0008.
• Harder: a wrapped action needs everything Buildroot's make expects to find: a configured output tree, stamps, the per-package directories. Faking that consistently is most of pkg_action.py.