Ethereum flavored WebAssembly (ewasm)

Specification Revision 4

This repository contains documents describing the design and high-level overview of ewasm. Expect the contents of this repository to be in flux: everything is still under discussion.

This repository is also available through ReadTheDocs.

What is WebAssembly?

WebAssembly (or Wasm as a contraction) is a new, portable, size- and load-time-efficient format. WebAssembly aims to execute at native speed by taking advantage of common hardware capabilities available on a wide range of platforms. WebAssembly is currently being designed as an open standard by a W3C Community Group.

Please review the WebAssembly design and instruction set first. (You can also make a pull request or raise an issue at the Wasm Github repo.)

A few key points:

WebAssembly defines an instruction set, intermediate source format (wast) and a binary encoded format (wasm).
WebAssembly has a few higher level features, such as the ability to import and execute outside methods defined via an interface.
LLVM includes a WebAssembly backend to generate Wasm output.
Major browser JavaScript engines will notably have native support for

WebAssembly, including but not limited to: Google's V8 engine (Node.js and Chromium-based browsers), Microsoft's Chakra engine (Microsoft Edge), Mozilla's Spidermonkey engine (Firefox and Thunderbird).

Other non-browser implementations exist too:

wasm-jit-prototype (a standalone VM using an LLVM backend), wabt (a stack-based interpreter), ml-proto (the OCaml reference interpreter), etc.

What is Ethereum flavored WebAssembly (ewasm)?

ewasm is a restricted subset of Wasm to be used for contracts in Ethereum.

ewasm:

specifies the VM semantics

specifies the semantics for an ewasm contract* specifies an Ethereum environment interface to facilitate interaction with the Ethereum environment from an ewasm contract*

specifies system contracts
specifies metering for instructions
and aims to restrict non-deterministic behavior
specifies a backwards compatible upgrade path to EVM1

Goals of the ewasm project

To provide a specification of ewasm contract semantics and the Ethereum interface* To provide an EVM transcompiler*, preferably as an ewasm contract To provide a metering injector*, preferably as an ewasm contract

To provide a VM implementation for executing ewasm contracts
To implement an ewasm backend in the Solidity compiler
To provide a library and instructions for writing contracts in Rust
To provide a library and instructions for writing contracts in C

Glossary

Ewasm contract*: a contract adhering to the ewasm specification Ethereum environment interface (EEI)*: a set of methods available to ewasm contracts metering*: the act of measuring execution cost in a deterministic way metering injector*: a transformation tool inserting metering code to an ewasm contract EVM transcompiler*: an EVM bytecode (the current Ethereum VM) to ewasm transcompiler. See this chapter.