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Currently, I do some experiments with Geth-EVM and opcode execution. During the experiments, I observed that the DIFFICULTY opcode always pushs 0x0 to the EVM stack regardless of how I set the difficulty value in the genesis config.file. How can I interpret this and how can I define the difficulty value?

I execute the EVM with the following command: 

/home/user/ethereum/evms/geth-evm-1.8.0-stable 
--code 5a5b5b325932443a4332364333348942594458453441344130349944585b600960d360513900 
--prestate /home/user/ethereum/geth_genesis.json 
--gas 1048575 --sender 0x054fcf7870c50924ecbddd38c26e159d2cc78232 
--receiver 0xa31741b8972eea1991a9093284ad16bab63b9c18 --nomemory --json run

This is my genesis config file: 

{"alloc": {
"0x123456789a123456789a123456789a123456789a": {
  "balance": "0x2bcb2dca0cded",
  "code": "0x1337",
  "nonce": "0x0"
},
"0x123456789a123456789a123456789a123456789c": {
  "balance": "0x9a815cb917edb",
  "code": "0x1337",
  "nonce": "0x0"
},
"0x123456789a123456789a123456789a123456789e": {
  "balance": "0x1c63ab403d7514",
  "code": "0x1337",
  "nonce": "0x0"
},
"0x123456789a321232189a123456789a123456789f": {
  "balance": "0xd3f6cdb0ae123",
  "code": "0x1337",
  "nonce": "0x0"
},
"0x333456789a123456789a123453289a1234512893": {
  "balance": "0x26b012410311d",
  "code": "0x1337",
  "nonce": "0x0"
}
},
    "coinbase": "0x0000000000000000000000000000000000000000",
    "config": {
        "byzantiumBlock": 0,
        "daoForkBlock": 0,
        "eip150Block": 0,
        "eip155Block": 0,
        "eip158Block": 0,
        "homesteadBlock": 0
},
    "difficulty": "0x01",
    "extraData": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "gasLimit": "0x3D0900",
    "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "nonce": "0x0000000000000000",
    "number": "0x00",
    "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "timestamp": "0x00"
}
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1 Answer 1

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You can't use difficulty lower than 2048 because the function that calculates the difficulty divides it by 2048 and if you use 1, you will end up with 0 since it is an integer division ( 1 / 2048 = 0). This parameter is configurable in 

config/protocol_params.go

DifficultyBoundDivisor

Try to set it to 1, maybe it will work. But if you don't want to have these problems, just set your difficulty to 2100 or above

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  • I understand that, but regardless of the value it always pushes 0x0 to the stack. During the last execution I set the value to "0x9999999" and i got 0x0.
    – kedenk
    Jul 18, 2018 at 13:51
  • try to "push" GasLimit, if it is not 0, then it is the divisor.
    – Nulik
    Jul 18, 2018 at 14:31
  • I will try that. However, I tested the same bytecode sequence with with the Parity implementation of EVM. This implementation takes exactly the difficult value from the genesis file. Is there a reason why Geth uses the divisor?
    – kedenk
    Jul 18, 2018 at 18:20
  • the divisor is part of the difficulty function, everybody has it implemented the same way otherwise you will not reach consensus. To run bytecode you have to have a preinitialized environment , in other words , a types.Header, a state.StateDb and vm.Context objects. In your case Difficulty is 0 , this means types.Header is not initialized, Alter the function vm.NewEVM() and dump all the parameters passed to this function to console, this way you will have a better understanding of what part of the enviroment is not configured properly.
    – Nulik
    Jul 18, 2018 at 20:47
  • I will try this. But actually I use the standalone EVM executable. So types.Header should be initialized?!
    – kedenk
    Jul 19, 2018 at 18:06

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