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The missing libclang_rt.builtins-wasm32.a file to compile to WebAssembly.
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jedisct1 Use wasm32-wasi
Signed-off-by: Frank Denis <>
Latest commit 2f799ab May 18, 2019
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precompiled Import Apr 7, 2019 Use wasm32-wasi May 18, 2019


LLVM 8 can compile to WebAssembly out of the box.

If you are using macOS with Homebrew, or another 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 system.

WASI is the de facto standard, and can be compiled using a stock clang/LLVM 8 installation.

Its source code can be found here: WASI sysroot, and compiles fine even on non-Linux system.

Now you should be all set:

clang --target=wasm32-wasi --sysroot=/opt/wasi-sysroot -O2 test.c


Building an object file or library will work, but building a module will not, due to the libclang_rt.builtins-wasm32.a file missing.

You can either recompile clang_rt from the wasi-sdk repository to get it.

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.

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