This blog post series is written to help you understand how EVM works at a slightly lower level (assuming you have some solidity experience).
In this post, we’re going to use Remix IDE to write, compile, deploy and run smart contracts. We’ll be working with the 1_Storage.sol contract found by default in Remix IDE.
pragma solidity 0.8.0;
contract Storage {
uint256 number;
function store(uint256 num) public {
number = num;
}
function retrieve() public view returns (uint256){
return number;
}
}
Compiling
Compile a contract in Remix IDE select Solidity Compiler tab on left side of window and click on compile 1_storage.sol button. Once the compilation is completed, select the Compilation Details Button.
You should see a popup containing everything the Solidity compiler generates on clicking Compilation Details button. The Solidity compiler generates various things on compilation, few of which are Bytecode, Runtime Bytecode and ABI.
On clicking on BYTECODE you should see a JSON object.
{
"generatedSources": [],
"linkReferences": {},
"object": "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",
"opcodes": "PUSH1 0x80 PUSH1 0x40 MSTORE CALLVALUE DUP1 ISZERO PUSH2 0x10 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST POP PUSH2 0x12F DUP1 PUSH2 0x20 PUSH1 0x0 CODECOPY PUSH1 0x0 RETURN INVALID PUSH1 0x80 PUSH1 0x40 MSTORE CALLVALUE DUP1 ISZERO PUSH1 0xF JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST POP PUSH1 0x4 CALLDATASIZE LT PUSH1 0x32 JUMPI PUSH1 0x0 CALLDATALOAD PUSH1 0xE0 SHR DUP1 PUSH4 0x2E64CEC1 EQ PUSH1 0x37 JUMPI DUP1 PUSH4 0x6057361D EQ PUSH1 0x51 JUMPI JUMPDEST PUSH1 0x0 DUP1 REVERT JUMPDEST PUSH1 0x3D PUSH1 0x69 JUMP JUMPDEST PUSH1 0x40 MLOAD PUSH1 0x48 SWAP2 SWAP1 PUSH1 0xC2 JUMP JUMPDEST PUSH1 0x40 MLOAD DUP1 SWAP2 SUB SWAP1 RETURN JUMPDEST PUSH1 0x67 PUSH1 0x4 DUP1 CALLDATASIZE SUB DUP2 ADD SWAP1 PUSH1 0x63 SWAP2 SWAP1 PUSH1 0x8F JUMP JUMPDEST PUSH1 0x72 JUMP JUMPDEST STOP JUMPDEST PUSH1 0x0 DUP1 SLOAD SWAP1 POP SWAP1 JUMP JUMPDEST DUP1 PUSH1 0x0 DUP2 SWAP1 SSTORE POP POP JUMP JUMPDEST PUSH1 0x0 DUP2 CALLDATALOAD SWAP1 POP PUSH1 0x89 DUP2 PUSH1 0xE5 JUMP JUMPDEST SWAP3 SWAP2 POP POP JUMP JUMPDEST PUSH1 0x0 PUSH1 0x20 DUP3 DUP5 SUB SLT ISZERO PUSH1 0xA0 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST PUSH1 0x0 PUSH1 0xAC DUP5 DUP3 DUP6 ADD PUSH1 0x7C JUMP JUMPDEST SWAP2 POP POP SWAP3 SWAP2 POP POP JUMP JUMPDEST PUSH1 0xBC DUP2 PUSH1 0xDB JUMP JUMPDEST DUP3 MSTORE POP POP JUMP JUMPDEST PUSH1 0x0 PUSH1 0x20 DUP3 ADD SWAP1 POP PUSH1 0xD5 PUSH1 0x0 DUP4 ADD DUP5 PUSH1 0xB5 JUMP JUMPDEST SWAP3 SWAP2 POP POP JUMP JUMPDEST PUSH1 0x0 DUP2 SWAP1 POP SWAP2 SWAP1 POP JUMP JUMPDEST PUSH1 0xEC DUP2 PUSH1 0xDB JUMP JUMPDEST DUP2 EQ PUSH1 0xF6 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST POP JUMP INVALID LOG2 PUSH5 0x6970667358 0x22 SLT KECCAK256 SWAP4 PUSH23 0x6D3EF49A9B971F198DD8517D2BDC41BBC80DD5B1F64394 STATICCALL DELEGATECALL AND RETURNDATASIZE 0xFC 0xB6 0xC8 PUSH5 0x736F6C6343 STOP ADDMOD STOP STOP CALLER ",
"sourceMap": "62:199:0:-:0;;;;;;;;;;;;;;;;;;;"
}
We’re interested in the "object" property of this JSON object.
BYTECODE Object will look like:
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
and similarly, you will be able to get RUNTIME BYTECODE Object from compilation details.
{ ...,
"immutableReferences": {},
"linkReferences": {},
"object": "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",
"opcodes": "PUSH1 0x80 PUSH1 0x40 MSTORE CALLVALUE DUP1 ISZERO PUSH1 0xF JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST POP PUSH1 0x4 CALLDATASIZE LT PUSH1 0x32 JUMPI PUSH1 0x0 CALLDATALOAD PUSH1 0xE0 SHR DUP1 PUSH4 0x2E64CEC1 EQ PUSH1 0x37 JUMPI DUP1 PUSH4 0x6057361D EQ PUSH1 0x51 JUMPI JUMPDEST PUSH1 0x0 DUP1 REVERT JUMPDEST PUSH1 0x3D PUSH1 0x69 JUMP JUMPDEST PUSH1 0x40 MLOAD PUSH1 0x48 SWAP2 SWAP1 PUSH1 0xC2 JUMP JUMPDEST PUSH1 0x40 MLOAD DUP1 SWAP2 SUB SWAP1 RETURN JUMPDEST PUSH1 0x67 PUSH1 0x4 DUP1 CALLDATASIZE SUB DUP2 ADD SWAP1 PUSH1 0x63 SWAP2 SWAP1 PUSH1 0x8F JUMP JUMPDEST PUSH1 0x72 JUMP JUMPDEST STOP JUMPDEST PUSH1 0x0 DUP1 SLOAD SWAP1 POP SWAP1 JUMP JUMPDEST DUP1 PUSH1 0x0 DUP2 SWAP1 SSTORE POP POP JUMP JUMPDEST PUSH1 0x0 DUP2 CALLDATALOAD SWAP1 POP PUSH1 0x89 DUP2 PUSH1 0xE5 JUMP JUMPDEST SWAP3 SWAP2 POP POP JUMP JUMPDEST PUSH1 0x0 PUSH1 0x20 DUP3 DUP5 SUB SLT ISZERO PUSH1 0xA0 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST PUSH1 0x0 PUSH1 0xAC DUP5 DUP3 DUP6 ADD PUSH1 0x7C JUMP JUMPDEST SWAP2 POP POP SWAP3 SWAP2 POP POP JUMP JUMPDEST PUSH1 0xBC DUP2 PUSH1 0xDB JUMP JUMPDEST DUP3 MSTORE POP POP JUMP JUMPDEST PUSH1 0x0 PUSH1 0x20 DUP3 ADD SWAP1 POP PUSH1 0xD5 PUSH1 0x0 DUP4 ADD DUP5 PUSH1 0xB5 JUMP JUMPDEST SWAP3 SWAP2 POP POP JUMP JUMPDEST PUSH1 0x0 DUP2 SWAP1 POP SWAP2 SWAP1 POP JUMP JUMPDEST PUSH1 0xEC DUP2 PUSH1 0xDB JUMP JUMPDEST DUP2 EQ PUSH1 0xF6 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST POP JUMP INVALID LOG2 PUSH5 0x6970667358 0x22 SLT KECCAK256 SWAP4 PUSH23 0x6D3EF49A9B971F198DD8517D2BDC41BBC80DD5B1F64394 STATICCALL DELEGATECALL AND RETURNDATASIZE 0xFC 0xB6 0xC8 PUSH5 0x736F6C6343 STOP ADDMOD STOP STOP CALLER ",
"sourceMap": "62:199:0:-:0;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;180:79;;;:::i;:::-;;;;;;;:::i;:::-;;;;;;;;110:64;;;;;;;;;;;;;:::i;:::-;;:::i;:::-;;180:79;221:7;246:6;;239:13;;180:79;:::o;110:64::-;164:3;155:6;:12;;;;110:64;:::o;7:139:1:-;;91:6;78:20;69:29;;107:33;134:5;107:33;:::i;:::-;59:87;;;;:::o;152:262::-;;260:2;248:9;239:7;235:23;231:32;228:2;;;276:1;273;266:12;228:2;319:1;344:53;389:7;380:6;369:9;365:22;344:53;:::i;:::-;334:63;;290:117;218:196;;;;:::o;420:118::-;507:24;525:5;507:24;:::i;:::-;502:3;495:37;485:53;;:::o;544:222::-;;675:2;664:9;660:18;652:26;;688:71;756:1;745:9;741:17;732:6;688:71;:::i;:::-;642:124;;;;:::o;772:77::-;;838:5;827:16;;817:32;;;:::o;855:122::-;928:24;946:5;928:24;:::i;:::-;921:5;918:35;908:2;;967:1;964;957:12;908:2;898:79;:::o"
}
Yeah. Those aren’t the most readable things you’ve ever seen.
Deployment
Now we need to deploy the contract. It’s fairly simple to deploy this contract via Remix on inbuilt Javascript EVM. To deploy a contract you simply need to set various params like Gas Limit, Gas Price, Value and then click on Deploy button in Deploy and Run transactions tab. It would deploy an instance of the Storage contract to its javascript EVM.
You can interact with the various public and external functions in the smart contract at the bottom in the Deploy and Run transactionscolumn under Deployed Contracts section.
But, What the heck is a Bytecode?
Bytecode is an executable code on EVM. Smart contract code is usually written in a high level programming language such as Solidity or Vyper. The high level code is compiled into bytecode and deployed to Ethereum. Later in the series we’ll look at how exactly the bytecode execution happens and what does the bytecode resemble.
Runtime vs Creation Bytecode
Creation code is the code that creates the contract. It includes constructor logic and constructor parameters of a smart contract along with all the other logic of a contract.
Runtime Bytecode is the code that is stored on-chain that describes a smart contract. This code does not include the constructor logic or constructor parameters of a contract, as they are not relevant to the code that was actually used to create the contract.
Runtime Bytecode is generated from creation code.
From our 1_storage.sol contract the Runtime and Creation code we got are:
Creation:
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
Runtime:
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
You can ctrl/cmd + f on the Runtime code to verify that it is in the Creation Code.
Next in the series we’ll try to decode bytecode and understand how function calls happen at a lower level.