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.

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.

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

• 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

• 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.

• FAQ
• Rationale
• VM semantics
• Ethereum environment interface
• Ewasm Contract Interface
• System contracts
• Backwards compatibility instructions
• Original Proposal (EIP#48)
• WebAssembly Specification
• WebAssembly design documents

• ewasm-tests
• wasm-metering
• ewasm-kernel
• evm2wasm
• ewasm-libc
• assemblyscript-ewasm-api
• ewasm-rust-api

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.

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