core: assign default difficulty to zero for chain without ethash #31067
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I hit this case while trying something with the simulated backend. The EVM only enables instruction set forks after the merge when 'Random' is set. In the simulated backend, the random value will be set via the engine API for all blocks after genesis. But for the genesis block itself, the random value will not be assigned in the vm.BlockContext because the genesis has a non-zero difficulty. For my case, this meant that estimateGas did not work for the first transaction sent on the simulated chain, since the contract contained a PUSH0 instruction. This could also be fixed by explicitly configuring a zero difficulty in the simulated backend. However, I think that zero difficulty is a better default these days.
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CI is failing |
| @@ -459,8 +459,12 @@ func (g *Genesis) toBlockWithRoot(root common.Hash) *types.Block { | |||
| if g.GasLimit == 0 { | |||
| head.GasLimit = params.GenesisGasLimit | |||
| } | |||
| if g.Difficulty == nil && g.Mixhash == (common.Hash{}) { | |||
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QQ, Why the g.MixHash == (common.Hash{}) is a condition for setting the genesis difficulty?
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I don't get it either. This code is very old.
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It was added in the PR that also added the RANDOM opcode. https://github.com/ethereum/go-ethereum/pull/24141/files#diff-1272116434e5549f278a940767af52ed2d1abc91c44fa04ec48d8835a3774036
@MariusVanDerWijden might know more.
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I think it might be related with the idea of how the header MixDigest is used. After the merge, this field was repurposed for the random value. What @MariusVanDerWijden may have been thinking is: "if Mixhash is set in genesis, it means the genesis block is supposed to have a random value (signaling the merge), and thus difficulty will be set to zero."
I hit this case while trying something with the simulated backend. The EVM only enables instruction set forks after the merge when 'Random' is set. In the simulated backend, the random value will be set via the engine API for all blocks after genesis. But for the genesis block itself, the random value will not be assigned in the vm.BlockContext because the genesis has a non-zero difficulty. For my case, this meant that estimateGas did not work for the first transaction sent on the simulated chain, since the contract contained a PUSH0 instruction.
This could also be fixed by explicitly configuring a zero difficulty in the simulated backend. However, I think that zero difficulty is a better default these days.