sergioandClaude Opus 4.8
bf3f1166ec
Rastrea las correcciones del frente rust que vivían en .scratch/ (gitignored): - run_rustc.patch (vs mrustc be69c74): minicargo/hello con --target musl; RUSTFLAGS + sitios de link con link-self-contained=no (CRT vía gcc Alpine, link dinámico contra musl); proxy host-units con crt-static off (sin inject de --target, host==target==musl con el stage0 musl-host). - build-stage0-musl.sh: rebuild del stage0 rustc+cargo con host triple musl (CFG_COMPILER_HOST_TRIPLE vía RUSTC_TARGET, --target vía MRUSTC_TARGET), reusa LLVM + bin/mrustc. Gotcha OUTDIR_SUF documentado. - run-runrustc.sh: corre targets de run_rustc en el sandbox devfs apuntando al stage0 musl-host. - README: diagnóstico de los 3 snags acoplados (std-gnu mmap64/open64, CRT self-contained ausente, host-triple gnu + proc-macros) y el workflow. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
81 lines
4.0 KiB
Markdown
81 lines
4.0 KiB
Markdown
# rust-frontier — self-hosting the builder's rust toolchain
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The last frontier of `selfhost-verify` variante (b): replace the Alpine
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`rustc/cargo 1.91.1` in `/toolchain` with a hammer-built rust, via the **purist
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mrustc chain** (no prebuilt rustc binary). Path:
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mrustc → rustc 1.90.0 (builds bundled LLVM) → 1.91.0 → 1.91.1
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These scripts + patch are the working artifacts. The mrustc tree itself lives in
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`.scratch/mrustc` (gitignored — it's a large third-party clone, upstream master
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`be69c74`); only our deltas are tracked here.
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## Files
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- **`run_rustc.patch`** — patch against mrustc `be69c74` for `run_rustc/Makefile`
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and `run_rustc/rustc_proxy.sh`. Apply from the mrustc root:
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`git -C .scratch/mrustc apply /path/to/run_rustc.patch`
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- **`build-stage0-musl.sh`** — rebuild the mrustc stage0 `rustc`+`cargo` with a
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**musl host triple** (`output-1.90.0-x86_64-unknown-linux-musl/`). Run inside
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the Alpine devfs sandbox (gcc, MRUSTC_TARGET_VER=1.90). Reuses the already-built
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LLVM and `bin/mrustc`.
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- **`run-runrustc.sh`** — run a `run_rustc` make target inside the devfs sandbox,
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pointed at the musl-host stage0.
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> Both runners hardcode `/home/sergio/hammer` and assume the prepared devfs at
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> `.dev-fs/alpine` (256-TLS-key musl loader + g++; see the bootstrap-devfs notes).
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## Why the patches exist (the snags)
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The lab is **musl-only** (Alpine devfs); the 4/4 inputs (arje-zero/hammerd) are
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built `--target x86_64-unknown-linux-musl`. Three coupled problems had to be fixed
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to bootstrap a usable rust there:
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1. **stage-1 std built for gnu** (`mmap64`/`open64` undefined at link).
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`minicargo` was invoked without `--target`, so it used mrustc's default **gnu**
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triple — and gnu std references glibc's LFS64 symbols that musl 1.2.5 doesn't
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export. Fix: pass `--target $(RUSTC_TARGET)` to minicargo (Makefile:162) and to
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the stage-1 smoke-test (Makefile:172). A correct musl std uses the **base** libc
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symbols (`open`/`mmap`/…), matching Alpine's reference std.
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2. **self-contained CRT absent.** musl's default link is `-static-pie` against a
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`lib/rustlib/<t>/lib/self-contained/` CRT dir that the mrustc sysroot never
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populates. Fix: `-C target-feature=-crt-static -C link-self-contained=no` so the
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Alpine gcc supplies crt1/crti/crtn + crtbeginS/crtendS and links dynamically
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against the system musl (RUSTFLAGS in Makefile:111, plus the per-link sites).
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3. **host-triple = gnu on a musl system** (the deep one). cargo compiles
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build-scripts and **proc-macros** for the *host*; mrustc's stage0 rustc has its
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host triple baked as `x86_64-unknown-linux-gnu` (not runtime-overridable). A
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proxy `--target musl` inject fixes build-script *bins*, but **proc-macros are
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dlopen'd and must match the host triple structurally** — injection makes them
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target artifacts that rustc rejects. Aliasing musl rlibs as gnu also fails:
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rustc reads the triple from rlib *metadata* (`E0461`), not the path.
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**The only fix is a stage0 rustc whose host triple is musl** — that's what
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`build-stage0-musl.sh` produces (`CFG_COMPILER_HOST_TRIPLE` via `RUSTC_TARGET`,
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`--target` via `MRUSTC_TARGET`). Then host==target==musl: cargo doesn't
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cross-compile, proc-macros load natively, and `rustc_proxy.sh` only needs the
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CRT flags (no `--target` inject).
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Gotcha: do **not** pass `OUTDIR_SUF` on make's command line — a command-line var
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can't be reassigned by the makefile, so the `-musl` suffix append is skipped and
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the build contaminates the gnu output dir. Let it default.
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## Workflow
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```sh
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# 1. apply the run_rustc patch into the mrustc clone
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git -C .scratch/mrustc apply scripts/rust-frontier/run_rustc.patch
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# 2. rebuild stage0 rustc+cargo with a musl host triple (~hours, reuses LLVM)
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.scratch/build-stage0-musl.sh # -> output-1.90.0-x86_64-unknown-linux-musl/
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# 3. build the optimised rustc + cargo via run_rustc (stage 1/2/3)
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.scratch/run-runrustc.sh all
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# 4. (next) climb 1.90.0 → 1.91.0 → 1.91.1, then swap rust into /toolchain
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```
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Full diagnostic history is in the `selfhost-verify-rust-frontier` memory.
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