This document discusses eWASM, which is the Ethereum Virtual Machine implemented using WebAssembly (WASM). Some key points: - eWASM mirrors the EVM stack-based design in WASM but uses locals instead of a deep stack and has a more RISC instruction set. - High-level EVM instructions are removed and replaced by importing standard interface functions defined in the Ethereum Environment Interface (EEI). - A system contract called Sentinel is used to insert metering statements and reject invalid eWASM bytecode before deployment. - eWASM has potential performance benefits over EVM but some challenges remain around storage model, metering approaches,

1. EWASM VM - 次世代的
Ethereum Virtual Machine
@hydai
2019/08/17

2. hydai
Blog: hyd.ai
Mail: hydai@hyd.ai
GitHub: @hydai
Work: @SecondState
Focus on Compiler and Virtual
Machine technology.

3. – Eth1x/Istanbul meetup Berlin
Save Ethereum,
Scale Ethereum.

4. EVM recap
• Stack-based virtual machine (or interpreter…)
• 256 bit stack items
• Too many high level instructions
• Storage(SSTORE, SLOAD)
• SHA3(keccak-256)
• Call, Create Contract…
• Too far away from actual machine architecture
• Less language support (Vyper, Solidity)

5. How about wasm?
• Also, a stack-based machine but…
• has locals ( ~= register or memory)
• only access top 3 items from stack v.s EVM’s 16
• Support 32/64 bit operations
• No high level instructions
• RISC Instruction Set, can map to a common CPU ISA
• Large community power
• Supported in all major browser
• Lots of implementations
• Lots of language support (C++, Rust, …)

6. wasm engine
• Tool
• binaryen (a toolkit contains an interpreter in C++)
• wabt (a toolkit contains an interpreter in C++)
• wavm (LLVM-based JIT)
• wagon (interpreter in Golang)
• parity-wasm (interpreter in Rust)
• Browser (hyper interpreter/JIT)
• Chrome (V8)
• Edge (chakra)
• Firefox (spidermonkey)

7. What is ewasm?
• ewasm ⊂ wasm
• NOT support floating point number
• LIMITED imports and exports (wasm section)
• Will inject bytecode metering and has runtime
metering

8. Where did the high level
instructions go?

9. Ethereum Environment Interface
• EEI defines a set of ewasm imported functions
• With standard interface, clients can implement
easier
• Because EEI is not native instructions in bytecode
• Quick prototyping and doing specific upgrades
ewasm module EEI blockchain

10. Definition
Use

11. How about
Invalid instructions issues?

12. System Contract
• Compiled into wasm bytecode
• Deployed on chain (like normal contract)
• Or be part of client (like precompiles)
• Examples:
• Byzantium precompiles
• sha256, ripemd160, ecrecover, modexp, …
• Use upper-bound metering
• Sentinel (verification and metering)

13. Sentinel Contract?
• Before contract deployment
• Reject non-ewasm bytecode (e.g. floating point)
• Insert metering statements
• basic-block-based metering (call useGas in the beginning
of block)
ewasm
bytecode
Sentinel
deployed
on chain

14. ewasm stack

15. Client
with EVM-C support
EVM-C
Heru
Wasm Engine in C++
EEI
Runtime
ewasm
bytecode
Sentinel

16. EVM-C
• Connect client and VM implementation
• Ethereum Virtual Machine includes EVM1 and eWASM
• With EVM-C, VM can be linked statically or loaded
as plugin (.dll, .so)
• C means C language API

17. wasm sections
src: https://rsms.me/wasm-intro

18. wasm engine
ewasm
bytecode
Parse
ewasm
module
Validate
validated
ewasm module
Instantiate
ewasm
module
instance
Execute

19. Is ewasm a panacea for
ethereum?

20. Calm Down

21. Issue 1 - Storage Model
• eWASM = EVM 1.0 mirrored in wasm
• Storage model is not compatible with rent
• Here comes eWASM 1.X!!!
• New storage model designed for rent!!!

22. Issue 2 - Performance
Is eWASM always better than EVM1?

26. What happens?!!!!!
• General wasm engine supports 32/64 bit operations
• 128/256 bit operations will be simulated by 32/64
bit operations
• EVM has the precompiles……

27. Issue 3 - Metering
• Basic block metering
• Super block metering
• Upper bound metering

28. Basic Block Metering

29. Super Block Metering

31. Q & A

32. Reference
• ewasm for sharding
• https://drive.google.com/file/d/19t4qCqEK2RPt0p1XYx-
a2FdZSAlCq7H0/view
• ewasm updates
• https://drive.google.com/file/d/
1CRc0qBQTebNKw7NRZXzxbHovrigW0bqf/view
• ewasm design
• https://github.com/ewasm/design
• EEI
• https://github.com/ewasm/design/blob/master/eth_interface.md
• wasm-intro
• https://rsms.me/wasm-intro