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WASI libc implementation for WebAssembly
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Latest commit 8df0d4c Jul 12, 2019


This is a work in progress. It's usable for many purposes, though the APIs aren't stable yet.

What is this?

It's several things.

First, it's a usable libc. It builds a "sysroot" which can be pointed to by compilers, such as Clang 8.0, using the wasm32-wasi target. It's a work in progress, but it is already sufficient to run basic programs.

Second, it's a "reference" implementation, which means the interfaces defined here can be used by other tools and libraries, even if they don't use all the actual implementations here. For example, we don't expect everyone will want to use the exact malloc implementation provided here, but tools and libraries using an ABI-compatible malloc interface will be able to interoperate regardless of which actual implementation is used.

Third, it's an example showing the use of the WASI API. The libc functionality is implemented using calls to WASI functions.


The easiest way to get started with this is to use one of the prepackaged releases.

Building from source

To build a WASI sysroot from source, obtain a WebAssembly-supporting C compiler (currently this is only clang 8+, though we'd like to support other compilers as well), and then run:

make WASM_CC=/path/to/clang/with/wasm/support \
     WASM_AR=/path/to/llvm-ar \

This makes a directory called "sysroot", by default. See the top of the Makefile for customization options.

To use the sysroot, use the --sysroot= option:

/path/to/wasm/supporting/c/compiler --sysroot=/path/to/the/newly/built/sysroot ...

to run the compiler using the newly built sysroot.

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