Note: as of 2023, you should probably use the Zig SDK instead of this.
The 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 -rdyamic -Os -s -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.
Almost.
Unless your WebAssembly application is compute-only, you still need some kind of interface with the runtime.
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 wasi-sysroot
.
Now you should be all set. Just replace /opt/wasi-sysroot
with the location you extracted wasi-sysroot
to.
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
The missing libclang_rt.builtins-wasm32.a
can be obtained by recompiling compiler_rt
from LLVM.
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.
Copy libclang_rt.builtins-wasm32.a
from the tarball into the path expected by clang
, creating the lib
and wasi
directories if necessary, and you'll be all set!
This has been tested with:
- LLVM 10, 11, 12, 13, 14 (
llvm-10-to-14
folder) - LLVM 15, 16
- LLVM 17
- LLVM 18