OpenZeppelin’s Blog post

https://blog.openzeppelin.com/deconstructing-a-solidity-contract-part-ii-creation-vs-runtime-6b9d60ecb44c

Opcodes

• PUSH

  88 PUSH1 0x04
  |  |     |
  |  |     Hex value for push.
  |  Opcode.
  Instruction number.
  

• PUSH1 vs PUSH2

• ADD
• SWAP
• DUP
• JUMP
• JUMPI
• JUMPDEST
• RETURN
• STOP
• MLOAD(ptr)
  • Loads a 32‑byte word from memory at a given address and pushes it onto the stack.
  • [mem_address] → returns value stored at memory[mem_address ... mem_address+31]
• MSTORE (ptr,value)
  • Opcode: 0x55
  • Writes a 32‑byte word from the stack into memory at a specified memory address
  • MSTORE(ptr, value )
• SWAP2
  • swaps the top-of-stack element (stack[-1]) with the third-from-top element (stack[-3])
• SSTORE
  • SSTORE (opcode 0x55) writes a value into the contract’s persistent storage.
  • It pops two values off the stack:
    1. Key: the 32-byte storage slot identifier
    2. Value: the 32-byte data to store
• ISSZERO
  • Opcode: 0x15 (decimal 21)
  • It takes one input from the stack, checks if it equals zero, and pushes a boolean result:
    • Pushes 1 (true) if the input is zero
    • Pushes 0 (false) otherwiseEthereum Stack Exchange+5
• CALLDATASIZE

  • Pushes a single value onto the EVM stack: the length of calldata in bytes.

  • Calldata consists of a “function id”, which is generated by hashing the function’s signature (truncated to the first leading four bytes) followed by the packed arguments data. That is ,

  • Calldata is the read-only byte array that includes:

    1. Function selector (first 4 bytes)
    2. Encoded arguments (rest of the bytes)
    3. example,

    function transfer(address to, uint amount) external;

    a9059cbb // function selector (transfer), got by applying keccak256(totalSupply()) 000000000000000000000000deadbeef... // address to 000000000000000000000000000000000000000000000000000000000000003e // amount

    // This calldata would be 4 (selector) + 32 + 32 = 68 bytes, or 0x44