Import clang kickstart guide

README.md

@@ -89,7 +89,8 @@ One of the [design goals](https://github.com/ewasm/design/blob/master/rationale.
 
 At present, we've developed support for the following languages and toolchains:
 
-- LLVM: C, C++, and Rust: documentation pending
+- [C/C++ (LLVM) WebAssembly tutorial](./clang.md)
+- Rust: documentation pending
 - [AssemblyScript](https://github.com/AssemblyScript/assemblyscript), a subset of TypeScript, which uses the JavaScript toolchain: see the [etherts org](https://github.com/etherts/docs) for more information on writing contracts in AssemblyScript.
 
 If you're interested in adding support for another language, framework, or toolset, see the Contributing section above and reach out.

clang.md

@@ -0,0 +1,54 @@
+# Compiling C/C++ to WebAssembly
+
+## Rolling your own compiler
+
+Clang has a WebAssembly target, though it is not easy to use currently. First, a custom build must be made.
+
+To build `clang`:
+```sh
+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 -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=WebAssembly -DLLVM_TARGETS_TO_BUILD= ..
+cmake --build .
+cd ../..
+```
+
+This will take anything from 1 to 5 hours.
+
+To build `binaryen`:
+```sh
+git clone https://github.com/WebAssembly/binaryen.git
+cd binaryen
+mkdir build
+cd build
+cmake ..
+cmake --build .
+cd ../..
+```
+
+## Using this compiler
+
+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](https://github.com/webassembly/wabt) (previously called *sexpr-wasm-prototype*).
+
+Cheat sheet:
+```sh
+clang -emit-llvm --target=wasm32-unknown-unknown-elf -nostdlib -S hello.c
+llc -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.