引介｜EVM 深入探讨 Part 2

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;
/** * @title Storage * @dev Store & retrieve value in a variable */contract Storage {
    uint256 number;
    /**     * @dev Store value in variable     * @param num value to store     */    function store(uint256 num) public {        number = num;    }
    /**     * @dev Return value     * @return value of 'number'     */    function retrieve() public view returns (uint256){        return number;    }}

// SPDX-License-Identifier: MITpragma solidity ^0.8.3;
contract MemoryLane {
    function memoryLane() public pure {        bytes32[5] memory a;        bytes32[2] memory b;        b[0] = bytes32(uint256(1));    }}

////////////////////////////////////////// Free Memory Pointer Initialisation //////////////////////////////////////////
// value to store for free memory pointer 0x80 = 128 in decimalPUSH1 0x80// location for free memory pointer 0x40 = 64 in decimalPUSH1 0x40MSTORE
// jump location (required to prevent stack underflow) PUSH2 0xffff

//////////////////////////////////////////////////////////////////// Memory Allocation Varibale "a" & Free Memory Pointer Update /////////////////////////////////////////////////////////////////////
// load free memory pointerPUSH1 0x40MLOAD
// duplicate free memory pointerDUP1// 0xa0 = 160 in decimal, 32 * 5 = 160 first array is length 5PUSH1 0xa0// free memory pointer (0x80) + space for array (0xa0) = new free memory pointerADD// Save this new value 0x120 to the free memory locationPUSH1 0x40MSTORE

/////////////////////////////////////////// Memory Initialisation Varaible "a" ////////////////////////////////////////////// duplicate 0x80DUP1// push 0x05 = 5 in decimal (array length)PUSH1 0x05// Swap the top 2 items on the stack in this case 0x05 and 0x80SWAP1// push 0x20 = 32 in decimal (array item size)PUSH1 0x20// Duplicate the 3rd item on the stack in this case 0x05 to the top of the stackDUP3// 0x05 * 0x20 = 5 * 32 in decmial = 160 on top of the stack (size of array in bytes)MUL// Duplicate 0xa0 = 160 in decimalDUP1// Returns size of calldata in bytes currently just function signature = 0x04 or 4 in decmialCALLDATASIZE// duplicate 4th item on stack (0x80)DUP4// 0x80 (byte offset in the memory where the result will be copied.), 0x04 (byte offset in the calldata to copy.), 0xa0 (byte size to copy.) this offsets the 4 bytes in our call data with a size of 0xa0 which yeild a 160 bit set of 0's to be stored at the free memory pointer location// this effectively initialises our array in memory CALLDATACOPY// The remaining lines in this section manipulate the stack to ensure we have the memory location of variable "a" and removes any items that are no longer needed// duplicate 0xa0DUP1// duplicate 0x80DUP3// new free memory pointer as beforeADD// swap 1st (0x120) item on the stack and 3rd (0x80)SWAP2// pop top item off stack (0x80)POP// pop top item off stack (0xa0)POP// Swap top 2 items 0x120 & 0x05SWAP1// pop top item off stack (0x05)POP// pop top item off stack (0x120)POP// swap top 2 items 0x80 & 0xb6 (jump location)SWAP1// simulating a JUMP remove the top item off stack with POPPOP// Simulated jump locationPUSH2 0xffff// Simulated jump locationPUSH2 0xffff// simulating a JUMP, remove the top item off stack with POPPOP

/////////////////////////////////////////////////////////////////// Memory Allocation Varibale "b" & Free Memory Pointer Update ///////////////////////////////////////////////////////////////////
// free memory pointer load in PUSH1 0x40MLOAD// duplicate free memory pointer (0x120)DUP1// 0x40 = 64 in decimal, 32 * 2 = 64 second array is length 2PUSH1 0x40// free memory pointer (0x120) + space for array (0x40) = new free memory pointerADD// save new free memory pointer value at free memory location 0x40PUSH1 0x40MSTORE

////////////////////////////////////////// Memory Initialisation Variable "b" //////////////////////////////////////////// duplicate 0x120 (memory start location for variable "b")DUP1// 0x02 = 2 in decimal = array lengthPUSH1 0x02// swap top 2 items 0x02 & 0x120SWAP1// 0x20 = 32 in decimal (array item size in bytes)PUSH1 0x20// duplicate 3rd item on the stack 0x02DUP3// 0x02 * 0x20 = 0x40 = 64 (amount of bytes in memory to initialise)MUL// duplicate 0x40 (free memory pointer location)DUP1// same as before 4 bytes for function signature 0x04CALLDATASIZE// duplicate 4th item on the stack = 0x120DUP4// 0x120 (byte offset in the memory where the result will be copied.), 0x04 (byte offset in the calldata to copy.), 0x40 (byte size to copy.)CALLDATACOPY// The remaining lines in this section manipulate the stack to ensure we have the memory location of variable "a" and removes any items that are no longer needed//duplicate the top of the stack 0x40DUP1// duplicate 3rd item on the stack 0x120DUP3// add together yields free memory pointer valueADD// swap 0x160 & 0x120SWAP2// pop top item off stack (0x120)POP// pop top item off stack (0x40)POP// swap 0x160 & 0x02SWAP1// pop top item off stack (0x02)POP// pop top item off stack (0x160)POP// jump location to top of the stack 0xbeSWAP1// simulate jump pop jump location off stackPOP

//////////////////////////// Assign Value to b[0] ////////////////////////////// push 0x01, value to add b[0]PUSH1 0x01// push 0x00PUSH1 0x00// left shift operation no shift, first input is 0 SHL// duplicate 2nd item on stack (0x120)DUP2// push 0x00 = [0] where in the array should this item goPUSH1 0x00// push 0x20 = 64 bytes the length of the array PUSH1 0x02// duplicate 2nd item on stack (0x00)DUP2// 0x00 < 0x20 =  true = 0x01 (check the user is not trying to store a value at a location that doesn't exist in the array)LT// jump locationPUSH2 0x00d7// 2 POPs since this is a JUMPI (checking if LT returned true or false)// simulate JUMPI POP// simulate JUMPI POP// push 0x20 (32 bytes aray item size)PUSH1 0x20// 0x20 * 0x00 = 0x00 = 0 in decimal (array item size * index to determine byte offset)MUL// 0x00 + 0x120ADD// duplicate 2nd on stack 0x01 (value for b[0])DUP2// duplicate 2nd on stack 0x120 (memory location for b[])DUP2// store 0x01 at memory location 0x120MSTORE// clean up stackPOPPOPPOPPOP