GAS opcode should be included in purity checker about casper

[ralexstokes]

@gitcoinbot i do not have a WIP PR yet but i will soon.

[djrtwo]

Purity of contracts defined by this purity checker need to give a deterministic output only on the parameters pass in, not on the state of the blockchain at the time. An example could be something like the following:

def true_if_even_gas():
    return GAS % 2 == 0

This function is not deterministic on its inputs but rather on the state of the context of its execution. If a validator's signature had such a triviality, they could sign a message that would validate as True in one context but not in another. Thus opening up the potential of being able to sign nefarious messages and not get slashed for it.

[ralexstokes]

@gitcoinbot refer #169

[ralexstokes]

@gitcoinbot checking in

[djrtwo]

@gitcoinbot This is completed

[ralexstokes]

@gitcoinbot we are working to close out this bounty

[paulhauner]

When playing around with tests today, I noticed the following items are not currently blacklisted:

• 0xfb CREATE2
• A bunch of unused opcodes (I mention this because some of the unused opcodes are blacklisted in the current implementation)

I assume these will get fixed when it migrates to LLL. I just wanted to put them somewhere for reference.

[ChihChengLiang]

maybe try pytest xfail feature? so we can get that test work when GAS opcode implemented.

A xfail means that you expect a test to fail for some reason. A common example is a test for a feature not yet implemented, or a bug not yet fixed.
https://docs.pytest.org/en/documentation-restructure/how-to/skipping.html

[gitcoinbot]

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Work has been started.

These users each claimed they can complete the work by 4 months, 1 week from now. Please review their questions below:

1. ralexstokes has started work.

• Q: I will incorporate the changes detailed in this PR description and some of the comments on this issue. The changes all seem pretty straightforward.

[gitcoinbot]

@ralexstokes Hello from Gitcoin Core - are you still working on this issue? Please submit a WIP PR or comment back within the next 3 days or you will be removed from this ticket and it will be returned to an ‘Open’ status. Please let us know if you have questions!

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[gitcoinbot]

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[gitcoinbot]

@ralexstokes Hello from Gitcoin Core - are you still working on this issue? Please submit a WIP PR or comment back within the next 3 days or you will be removed from this ticket and it will be returned to an ‘Open’ status. Please let us know if you have questions!

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[ralexstokes]

@paulhauner nice catch on these opcodes! my take is this:

we should leave CREATE2 alone for now as it is still reserved.

and the other reserved opcodes i can find are 0x46-0x4f which are all in the "block information" family of opcodes. I'm guessing those were included in the original purity checker as they will always be impure no matter what.

the rest of the opcodes in the original purity checker are included in the Metropolis yellow paper opcode table.

[ralexstokes]

@djrtwo trying to come up with a good rationale why we need to add this opcode.

if we want to take the view that the purity checker is looking for purity with respect to the incoming transaction, i would say that GAS is pure. the reasoning is that the mutable data here gaslimit will be just another parameter to the valcode execution so we get referential transparency.

does anyone see this differently? do i misunderstand the semantics of purity checker?

it is straightforward to add an additional opcode here and i can do so if it makes sense

i would also point out the meta-issue (possibly a convo to have in another thread) about how and why the purity checker could change -- this touches on some of the stuff @paulhauner was getting at in his comment as well

[gitcoinbot]

@ralexstokes Hello from Gitcoin Core - are you still working on this issue? Please submit a WIP PR or comment back within the next 3 days or you will be removed from this ticket and it will be returned to an ‘Open’ status. Please let us know if you have questions!

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[vs77bb]

@djrtwo @ralexstokes Awesome!

[gitcoinbot]

@ralexstokes Hello from Gitcoin Core - are you still working on this issue? Please submit a WIP PR or comment back within the next 3 days or you will be removed from this ticket and it will be returned to an ‘Open’ status. Please let us know if you have questions!

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[vs77bb]

Hi @ralexstokes if you can 'Submit Work' for this one too, that'd be great.

[gitcoinbot]

Issue Status: 1. Open 2. Started 3. Submitted 4. Done

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Work for 80.0 DAI (80.0 USD @ $1.0/DAI) has been submitted by:

1. @ralexstokes

@gdipri01 please take a look at the submitted work:

• PR by @ralexstokes

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Issue Status: 1. Open 2. Started 3. Submitted 4. Done

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