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.

Resources

Projects

Design Process & Contributing

For now, high-level design discussions should continue to be held in the design repository, via issues and pull requests. Feel free to file issues.

Chat

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ewasm/design

ewasm

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