cmd/utils: require TTD and difficulty to be zero at genesis for dev mode

[fselmo]

Related to #29469 as that doesn't seem resolved if the user sets their own genesis config. I also discovered TTD can be negative and I could trick the correct state by setting TTD = -1 and difficulty = 0 since 0 difficulty is what triggers the correct EVM rules. This PR also validates that negative values are not accepted.

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If genesis config is set by the user, difficulty must be > TTD. However, if TTD is 0 and we are post-merge, setting difficulty > 0 will use the wrong EVM fork rules and raise issues like:

WARN [04-18|09:34:02.022] Served eth_estimateGas                   reqid=3 duration="419.912µs" err="invalid opcode: PUSH0"

I'm not sure if this is the best way to resolve it but if the user can set both to 0 at genesis, that makes sense that we'd be in a state where the difficulty is 0 and we are at TTD - which seems to be required for correct EVM rules. Perhaps a better message is needed for when TTD is set to 0 and difficulty is >0. As of right now, that would just end up using incorrect EVM rules which might be confusing to the user.

I can confirm this works as expected for me. Setting TTD = 0 and difficulty = 0, I get correct EVM rules. I can also no longer set TTD = -1 and difficulty = 0 to trick the EVM rules to trigger.

Thoughts?

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edit: I think a better UX may be to only allow TTD = 0 and difficulty = 0 for dev mode (see my comment below). If that's the case I can force push the change here.

Note: I've updated the code to be this latter option instead of validating any other values for TTD and difficulty.

[fselmo]

Alternatively, to get rid of any ambiguity, since it is already the case that terminalTotalDifficultyPassed must be true in developer mode:

if genesis.Config.TerminalTotalDifficulty.Cmp(big.NewInt(0)) != 0 {
	Fatalf("Bad developer-mode genesis configuration: terminalTotalDifficulty must be 0 in developer mode")
}
if genesis.Difficulty.Cmp(big.NewInt(0)) != 0 {
	Fatalf("Bad developer-mode genesis configuration: difficulty must be 0 in developer mode")
}

This seems to be reasonable and probably the best UX out of the two options. Unless there's a good reason to allow arbitrary TTD and difficulty in dev mode. It seems like the difficulty will have to be reset to 0 anyhow to trigger the correct EVM rules as it stands. Perhaps TTD can be validated that it is any arbitrary number above 0, but difficulty should always be 0 if we are post-merge.

[jwasinger]

Alternatively, to get rid of any ambiguity, since it is already the case that terminalTotalDifficultyPassed must be true in developer mode:

if genesis.Config.TerminalTotalDifficulty.Cmp(big.NewInt(0)) != 0 {
	Fatalf("Bad developer-mode genesis configuration: terminalTotalDifficulty must be 0 in developer mode")
}
if genesis.Difficulty.Cmp(big.NewInt(0)) != 0 {
	Fatalf("Bad developer-mode genesis configuration: difficulty must be 0 in developer mode")
}

This seems to be reasonable and probably the best UX out of the two options. Unless there's a good reason to allow arbitrary TTD and difficulty in dev mode. It seems like the difficulty will have to be reset to 0 anyhow to trigger the correct EVM rules as it stands.

I added the same validation in #29566 but opted to close it. My thinking is that there is no valid reason for a user to change these. If we go the route of trying to catch every possible misconfiguration that a user could make, we will end up with bloated validation logic that hurts readability.

[fselmo]

Ah, well. It's fairly difficult to discern what's going on currently if those values are set since even though shanghaiTime and cancunTime are turned on, PUSH0 is not available. I think perhaps some sort of validation that the user can't set them might be helpful? But obviously I'll leave that decision for y'all to decide. I can only speak to the user experience definitely being better with these stricter guidelines in place. Thanks for the quick response 👍🏼

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edit: With a custom genesis, I don't believe it's possible to leave these values alone also

[jwasinger]

I would retain the genesis.Config.TerminalTotalDifficulty == nil check above where we check that it is 0. but otherwise, LGTM.

[fselmo]

I would retain the genesis.Config.TerminalTotalDifficulty == nil check above where we check that it is 0. but otherwise, LGTM.

Changed to keep null pointer check 👍🏼