WebAssembly kickstart guide

README.md

WebAssembly kickstart guide

Rolling your own compiler

One of the premises of WebAssembly is to support compiling multiple languages to WebAssembly.

C/C++

Building

Clang has a WebAssembly target, though it is not easy to use currently. First, a custom build must be made.

To build clang:

git clone http://llvm.org/git/llvm.git
cd llvm/tools
git clone http://llvm.org/git/clang.git
cd ../projects
git clone http://llvm.org/git/compiler-rt.git
mkdir ../build
cd ../build
cmake -G Ninja -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=WebAssembly -DLLVM_TARGETS_TO_BUILD= ..
ninja
cd ../..

Also possible to build using POSIX make:

cmake -G "Unix Makefiles" -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=WebAssembly -DLLVM_TARGETS_TO_BUILD= ..
make -j 4

This will take anything from 1 to 5 hours.

To build binaryen:

git clone https://github.com/WebAssembly/binaryen.git
cd binaryen
mkdir build
cd build
cmake -G Ninja ..
ninja
cd ../..

Using

Now everything is set to finally compile Hello World!

The compilation process has four steps:

• compiling (clang)
• linking to LLVM IR (llc)
• compiling to WebAssembly S-expressions (s2wasm)
• compiling to WebAssembly binary (wasm-as)

Note: the last step can also be accomplished with wabt (previously called sexpr-wasm-prototype).

Cheat sheet:

clang -emit-llvm --target=wasm32 -nostdlib -S hello.c
llc -march=wasm32 -o hello.s hello.ll
s2wasm -o hello.wast hello.s
wasm-as -o hello.wasm hello.wast

There you go, you have your very first WebAssembly binary.

note: need to install lib32-glibc from multilib on arch

--target=wasm32 must be replaced with --target=wasm32-unknown-unknown-elf as the former will cause LLVM to generate __get_global statements, etc that s2wasm does not understand.