Note: as of 2021, you should probably use the Zig SDK instead of this.
zig cc command supports cross-compilation to WASI out of the box, without having to install these
builtins or the WASI SDK.
zig cc --target=wasm32-wasi -shared -Os -o module.wasm module.c
Starting with version 8 (and version 9 if you need WASI), LLVM can compile to WebAssembly out of the box.
If you are using macOS with Homebrew, or any operating system with up-to-date LLVM packages, you're all set.
Unless your WebAssembly application is compute-only, you still need some kind of interface with the runtime, namely WASI.
In order to do so, you may want to download and extract
wasi-sysroot. Note that you don't need
wasi-sdk if you already have LLVM, only
Now you should be all set. Just replace
/opt/wasi-sysroot with the location you extracted
clang --target=wasm32-wasi --sysroot=/opt/wasi-sysroot -O2 test.c
Dang. You may see
clang now complaining about a missing file:
wasm-ld: error: cannot open .../lib/wasi/libclang_rt.builtins-wasm32.a: No such file or directory
libclang_rt.builtins-wasm32.a can be obtained by recompiling
clang-rt from the
Or directly download that file here: libclang_rt.builtins-wasm32.a.
It is now also distributed with the WASI SDK releases, as a separate tarball.
libclang_rt.builtins-wasm32.a from the tarball into the path expected by
clang, creating the
wasi directories if necessary, and you'll be all set!
This has been tested with:
- LLVM 10
- LLVM 11
- LLVM 12