To build the rust stdlib for Emscripten with emscripten-wasm-eh:

./main.sh <emscripten-version> <rust-version>

<rust-version> can be either a nightly date (YYYY-MM-DD) or a released stable version (X.Y.Z).

Nightly, e.g.:

./main.sh 3.1.74 2025-02-01

Stable, e.g.:

./main.sh 3.1.74 1.85.0

The resulting archive is named emcc-<emscripten-version>_<channel>-<rust-version>.tar.bz2, e.g. emcc-3.1.74_nightly-2025-02-01.tar.bz2 or emcc-3.1.74_stable-1.85.0.tar.bz2.

Why?

There are two other options that would seem better:

1. -Zbuild-std
2. Build a custom sysroot with https://github.com/RalfJung/rustc-build-sysroot/ or https://github.com/DianaNites/cargo-sysroot/.

-Zbuild-std doesn't work with panic=abort (rust-lang/cargo#7359) or with cargo freeze. Building a custom sysroot with rustc-build-sysroot or cargo-sysroot works with cargo freeze but has the same problem with panic=abort. Thus, I think the only reasonable way to go is to build the sysroot from the rust source directory.