WebAssembly in Blockchains

[sinahab]

WebAssembly is finding a home within blockchains.

As a non-web platform, blockchains have distinct requirements. We have compiled notes from projects across the space (Ethereum, Parity, Dfinity, and Truebit), and will use this session to give an overview of approaches and challenges to the wider community. Referenced in CG-04.

We will discuss the following points:

• An overview of the blockchain VM:

  • A coordination layer between the WebAssembly VM and blockchain state.

• The blockchain VM needs to be deterministic (for nodes to reach consensus within the distributed network):

  • Resource limits: stack depth & memory.
  • Floating point.
  • Other sources of indeterminism: instantiation of a module

• Blockchains meter resource utilization:

  • The mechanics of metering: insert metering instructions per branch after verification.
  • Time: metering for instructions
  • Space: metering for memory

• Typed traps

  • To enable symbolic execution and static analysis tools.

• Imports

  • Accessing the memory: a spec for non-browser-based VMs.
  • Async / promises.
  • Having a WebAssembly standard library which defines operating system syscall.

• Instrumentation:

  • Two parts: 1) what to collect, 2) how to collect it.
  • Introducing ways to inspect the stack.

• Backward compatibility

  • Good: WASM binaries starts with a distinct flag.
  • Existing projects: JULIA, evm2wasm.

• New WASM developments which will be helpful:

  • Multi-values
  • References types
  • Annotations
  • Capabilities

• New WASM developments which might not be helpful (due to non-determinism):

  • Threads (with shared memory).
  • GC
  • SIMD.

[aj07]

@sinahab did you had meeting on it? When will be the next meeting. I want to be part of it.

[lrettig]

@sinahab any interest in planning one of these for 2019?

[sinahab]

@lrettig – happy to help, though will probably not have the capacity to be the primary driver. What are you thinking?

[lrettig]

Did this happen last year? If so, are there any notes or recordings?

[binji]

Here are the meeting notes and slides from the April 2018 meeting: https://github.com/WebAssembly/meetings/blob/master/2018/CG-04.md#webassembly-in-blockchain

[lrettig]

Thanks @binji, this is awesome and very helpful.

Several of us are hoping/planning to attend CG-06 including @recmo, @axic, maybe @sinahab? I wonder if we don't have some interesting findings from the past year of work on Ethereum and related projects to share.

[binji]

@lrettig Sounds good! Feel free to send a PR to that document w/ with an agenda item, and who wants to lead the discussion. We haven't really started planning that meeting yet, so things may end up moving around a bit.