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Quick Start

Download SDK packages here.

About this repository

This repository contains no compiler or library code itself; it uses git submodules to pull in the upstream Clang and LLVM tree, as well as the wasi-libc tree.

The libc portion of this SDK is maintained in wasi-libc.

Upstream Clang and LLVM (from 9.0 onwards) can compile for WASI out of the box, and WebAssembly support is included in them by default. So, all that's done here is to provide builds configured to set the default target and sysroot for convenience.

One could also use a standard Clang installation, build a sysroot from the sources mentioned above, and compile with --target=wasm32-wasi --sysroot=/path/to/sysroot. In this scenario, one would also need the libclang_rt.builtins-wasm32.a objects available separately in the release downloads which must be extracted into $CLANG_INSTALL_DIR/$CLANG_VERSION/lib/wasi/.


This repository uses git submodule, to clone it you need use the command below :

git clone --recursive


The Wasm-sdk's build process needs some packages :

  • cmake
  • clang
  • ninja
  • python3

Please refer to your OS documentation to install those packages.


To build the full package:

cd wasi-sdk
NINJA_FLAGS=-v make package

The built package can be found into dist directory. For releasing a new version of the package on GitHub, see


A typical installation from the release binaries might look like the following:

export WASI_VERSION=20
tar xvf wasi-sdk-${WASI_VERSION_FULL}-linux.tar.gz


Use the clang installed in the wasi-sdk directory:

export WASI_SDK_PATH=`pwd`/wasi-sdk-${WASI_VERSION_FULL}
CC="${WASI_SDK_PATH}/bin/clang --sysroot=${WASI_SDK_PATH}/share/wasi-sysroot"
$CC foo.c -o foo.wasm

Note: ${WASI_SDK_PATH}/share/wasi-sysroot contains the WASI-specific includes/libraries/etc. The --sysroot=... option is not necessary if WASI_SDK_PATH is /opt/wasi-sdk. For troubleshooting, one can replace the --sysroot path with a manual build of wasi-libc.

Integrating with a CMake build system

Use a toolchain file to setup the wasi-sdk platform.

$ cmake -DCMAKE_TOOLCHAIN_FILE=${WASI_SDK_PATH}/share/cmake/wasi-sdk.cmake ...

or the wasi-sdk-thread platform

$ cmake -DCMAKE_TOOLCHAIN_FILE=${WASI_SDK_PATH}/share/cmake/wasi-sdk-pthread.cmake ...

Notes for Autoconf

Autoconf 2.70 now recognizes WASI.

For convenience when building packages that aren't yet updated, updated config.sub and config.guess files are installed at share/misc/config.* in the install directory.

Docker Image

We provide a docker image including WASI SDK that can be used for building projects without a separate installation of the SDK. Autotools, CMake, and Ninja are included in this image, and standard environment variables are set to use WASI SDK for building.

For example, this command can build a make-based project with the Docker image.

docker run -v `pwd`:/src -w /src make

Take note of the notable limitations below when building projects, for example many projects will need threads support disabled in a configure step before building with WASI SDK.

Notable Limitations

This repository does not yet support C++ exceptions. C++ code is supported only with -fno-exceptions for now. Similarly, there is not yet support for setjmp/longjmp. Work on support for exception handling is underway at the language level which will support both of these features.

This repository experimentally supports threads with --target=wasm32-wasi-threads. It uses WebAssembly's threads primitives (atomics, wait/notify, shared memory) and wasi-threads for spawning threads. Note: this is experimental — do not expect long-term stability!

This repository does not yet support dynamic libraries. While there are some efforts to design a system for dynamic libraries in wasm, it is still in development and not yet generally usable.

There is no support for networking. It is a goal of WASI to support networking in the future though.