core/vm: set tracer-observable value of a delegatecall to match parent value

[ziogaschr]

This PR has been created after request at #26377 (comment)

Backwards compatibility

This is a breaking change in the tracing hooks API as well as semantics of the callTracer:

• CaptureEnter hook provided a nil value argument in case of DELEGATECALL. However to stay consistent with how delegate calls behave in EVM this hook is changed to pass in the value of the parent call.
• callTracer will return parent call's value for DELEGATECALL frames.

[s1na]

I'm considering setting the value directly to the hook in EVM. I.e. changing this:

go-ethereum/core/vm/evm.go

Line 318 in 2f73f4f

evm.Config.Tracer.CaptureEnter(DELEGATECALL, caller.Address(), addr, input, gas, nil)

To:

evm.Config.Tracer.CaptureEnter(DELEGATECALL, caller.Address(), addr, input, gas, caller.(*Contract).value)

Then all tracers would inherit this value. IMO this is right behavior, but this potentially affects people's scripts

[s1na]

I think we should make this change, since the whole CaptureEnter hook is a relatively new API.

[ziogaschr]

It's indeed fairly new, and it will return what's true.
Lucky shot is that nobody will have a check like value == nil, as it doesn't make sense in this context.

Give me the green light and I will change this, or feel free to commit the change :)

[holiman]

Start: from 000000000000000000000000000073656e646572 to 000000000000000000000000000000000000ff0a, value: 0x1337
  pc 0, op PUSH1, stack []
  pc 2, op PUSH1, stack [0x0]
  pc 4, op PUSH1, stack [0x0,0x0]
  pc 6, op PUSH1, stack [0x0,0x0,0x0]
  pc 8, op PUSH2, stack [0x0,0x0,0x0,0x0]
  pc 11, op GAS, stack [0x0,0x0,0x0,0x0,0xff0b]
  pc 12, op DELEGATECALL, stack [0x0,0x0,0x0,0x0,0xff0b,0x98966f]
   pc 0, op CALLVALUE, stack []
   pc 1, op ISZERO, stack [0x1337]
   pc 2, op STOP, stack [0x0]
  pc 13, op STOP, stack [0x1]

I wanted to verify that indeed, that's how the EVM works, it uses the parent callvalue for the `CALLVALUE1 op.

[holiman]

I agree with @s1na to change it on evm.go:L318. But, also add the comment from AsDelegate before doig the cast

	// NOTE: caller must, at all times be a contract. It should never happen
	// that caller is something other than a Contract.
	parent := c.caller.(*Contract)

[s1na]

From goerli tx:

{
    calls: [{
        from: "0x5b9ae6234cf1e447680c245200e066091e631bf3",
        gas: "0x649",
        gasUsed: "0x30b",
        input: "0x",
        to: "0x54ded98a6720eceaa54eb0f858c81737cde9ff9e",
        type: "DELEGATECALL",
        value: "0x650e1ca0690e"
    }],
    from: "0x26b17999f109b3ee24ef26a60495d5c583f3ee6f",
    gas: "0x8fc",
    gasUsed: "0x5cb",
    input: "0x",
    to: "0x5b9ae6234cf1e447680c245200e066091e631bf3",
    type: "CALL",
    value: "0x650e1ca0690e"
}

Except the callTracer no other built-in tracers uses value from CaptureEnter.

[holiman]

LGTM

[s1na]

LGTM! tests passed, only an unrelated flaky one failed. I restarted CI and will merge on green. Then merge this into #26377 and that will be ready to go too.