Based on my previous talk - Introduction to Ewasm 1.0 in COSCUP 2019 and lots of sessions in Ethereum devcon V, I remake this presentation to give an introduction to Ewasm 1.0 and 2.0.

1. Introduction to
Ewasm
Tai, Hung-Ying (hydai) @ Crosslink 2019
GitHub: @hydai
VP of Engineering, Second State
Slide: http://url.hyd.ai/LRFVT

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Agenda
EVM bytecode recap
WebAssembly (Wasm)
Ewasm 1.0
Ewasm 2.0

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EVM bytecode 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, ...)

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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 language support (C++, Rust, …)

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Wasm Section

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Wasm tooling
● 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)
○ wasmi (interpreter in Rust)
● Browser (hyper interpreter/JIT)
○ Chrome (V8)
○ Edge (chakra)
○ Firefox (spidermonkey)

7. Ewasm 1.0

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What is Ewasm 1.0
● Ewasm ⊂ wasm
● NOT support floating point number
● LIMITED imports and exports (wasm section)
● Will inject bytecode metering and has runtime metering

9. Where did the high
level instructions
go? (e.g. SHA)

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Ethereum Environment Interface (EEI)
● 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

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Definition

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Usage

13. How about
Invalid instructions
issues?

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System Contracts
● 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)

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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)

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Basic Block Metering (Injection)

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Ewasm Stack

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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

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Performance - Sha1
parity-evm 79.3ms
geth-evm 70.7ms
life 14.9ms
evmone 6.3ms
wasmi 5.6ms
wabt 3.1ms

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Performance - BN128mul
life 470ms
wasmi 390ms
wabt 106ms
parity-evm 18.0ms
geth-evm 2.3ms
evmone 553.0us

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What happens?!!!!!
● General wasm engine supports 32/64 bit operations
● 256 bit operations will be simulated by 32/64 bit
operations
○ ONE 256 bit operations may be replaced by 25 64 bit
operations
● As EVM provides precompiles, Wasm engine can support
`bignum` library to speed up.

22. Ewasm 2.0

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Questions about ETH 2.0
State Rent?
Cross-shard call?
Phase 2?
DevEx???

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Questions about ETH 2.0
State Rent?
Cross-shard call?
Phase 2?
DevEx???

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Questions about ETH 2.0
State Rent?
Cross-shard call?
Phase 2?
DevEx???

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Questions about ETH 2.0
State Rent?
Cross-shard call?
Phase 2?
DevEx???

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Execution Environments (EEs)
● “Contracts” are now called EEs
● EEs are Wasm bytecode
● EEs are executed on shards
● Shards only store a short (32-byte) state root for an EE
● On-shard execution goal is to verify the current state
root and calculate the new state root based on a
submitted proof and transactions

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Two Ewasms
● Ewasm 1.0 - Stateful, EVM-like design, with all the
legacy EVM brings
● Ewasm 2.0 - Stateless and pure execution oriented
design
● Can launch Ewasm 1.0 on Eth 1.0 if optimising EVM in
clients fails
● Can use Ewasm 1.0 contracts within EEs on Eth 2.0

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Stateful V.S. Stateless
https://github.com/gballet/presentations/blob/master/devcon/devconv/wasm_precompiles/compare_erc20.dot

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Phase One and Done - Very First Step
● Start simple - minimal execution
● Add EEs (Now we have code fields)
● Execute the EEs in shard blocks
● Here comes a testing tool - Scout!!!

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Open Questions
● How will cross-shard calls work?
○ Nobody knows
● How will the Eth1 switchover work?
○ Nobody is exactly sure.
● When Serenity?
○ January 3rd, MAYBE

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A MAYBE Roadmap
Phase one execution
Experiments with different EE
ETH1-esque environment with EVM/Ewasm
ETH1 -> ETH2 switchover

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What is Scout?
● An Eth 2.0 execution prototyping framework
● Based on “ETH 2.0 Phase 2 Proposal 2”
● Defines an API for the EEs (the EEI)
● Defines a test format (YAML format)
● Provides a tool which can execute on that format
● Provides example EEs

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EE(I)
● eth2::loadPreStateRoot(memoryOffset: u32ptr)
● eth2::blockDataSize() -> u32
● eth2::blockDataCopy(memoryOffset: u32ptr, offset:
u32, length: u32)
● eth2::savePostStateRoot(memoryOffset: u32ptr)
● eth2::pushNewDeposit(memoryOffset: u32ptr,
length: u32)

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EE: Hello World (in Rust)

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Playground
● SOLL - Compile your Solidity Smart Contract into
Ewasm via LLVM
○ Can deploy Ewasm bytecode on Ethereum Ewasm testnet
○ https://github.com/second-state/soll
○ Demo Video: https://youtu.be/X-A6sP_HTy0
● Scout - Ethereum 2.0 Phase 2 execution prototyping
engine
○ https://github.com/ewasm/scout

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Reference
● Ewasm overview and the precompile problem: Alex Beregszaszi and
Casey Detrio @ Ethereum Part 1 - YouTube
● Ewasm overview and the precompile problem: Alex Beregszaszi and
Casey Detrio @ Ethereum Part 2 - YouTube
● Wasm for blockchain&Eth2 execution: Paul Dworzanski,Alex
Beregszaszi,Casey Detrio@Ethereum Part 2 - YouTube
● Ewasm for sharding
● Ewasm updates
● Ewasm design
● wasm-intro

38. Thanks！