The forge · Stage of the build
SDK
Cross binutils, a patched GCC and musl, built on the Arch host. The first heating: here the metal's character is set, and every later stage depends on it.
What the SDK is
The SDK is the only part of the whole build that still trusts the Arch host. It compiles binutils and GCC so they run on x86_64-pc-linux-gnu but emit code for x86_64-saphira-linux-musl (historically x86_64-akadata-linux-musl from the original AKADATA Linux bootstrap), and it builds musl itself so the target libraries exist from day one.
The compiler that targets musl carries a small set of local patches, among them branch cost tuning applied to the GCC source before it is built. All inputs are pinned by hash before anything compiles, so the same SDK comes out of the tree every time it is asked for.
Completion is earned, not assumed. The stage records markers as it constructs the toolchain and passes an acceptance gate, and the final marker is only written once both are true. Everything downstream consumes this SDK and nothing else.
Continue the chain
Next: Stage 0, back to Arch Linux, or the forge overview.