Propose an ewasm subset for precompiles on the main chain

[axic]

The only features ewasm would need to expose are:

• useGas
• calldata access (calldatacopy/calldatasize)
• return / revert

This could be a way to get wasm VMs implemented and experimented with in a more controlled environment on the main chain.

It is not clear whether the precompiles would have "magic gas calculation rules" or just use "a metering process" on them.

[chfast]

BTW, can you pass reference to calldata buffer directly to the contract main function?

[axic]

Sample precompile in Rust: https://github.com/ewasm/ewasm-precompile-sha256/blob/master/src/lib.rs

[poemm]

Great idea. More generally, we can discuss how to constrain Wasm and EEI to get nice properties, such as allowing "magic gas calculation".

[axic]

Proposal to expose these functions from the EEI:

• useGas
• getCallDataSize
• callDataCopy
• getCaller (good for contracts like blockhash - or should be getTxOrigin?!)
• getCallValue (not necessary, but could be useful to reject calls with value)
• return
• revert