Can someone tell me you to pass an array argument to external function in assembly/yul?

Question

So far I have tried this:

    function swapEthForToken(
        address router,
        uint256 minAmount,
        address _tokenIn,
        address _tokenOut
    ) public payable {
        assembly {
            let path := mload(0x40)
            let deadline := add(timestamp(), 300)

            mstore(0x7c, SWAP_ETH_FOR_TOKEN)
            mstore(0x80, minAmount)
            // mstore(0xA0, path)
            mstore(path, 2)
            mstore(add(path, 0x20), _tokenIn)
            mstore(add(path, 0x40), _tokenOut)
            mstore(0xE0, address())
            mstore(0x100, deadline)

            let s1 := call(gas(), router, callvalue(), 0x7c, 0x100, 0x00, 0x40)

            if iszero(s1) {
                revert(0x00, 0x40)
            }
        }
    }

function I am trying to call is this:

    function swapExactETHForTokens(uint amountOutMin, address[] calldata path, address to, uint deadline)
        external
        payable
        returns (uint[] memory amounts);

Answer 1

You have to encode it following the solidity ABI specification https://docs.soliditylang.org/en/v0.8.21/abi-spec.html.

path is array of variable length, you have to encode an offset within the calldata, and at that offset encode the array. The call has 4 parameters so you will have to encode something like this:

offset data
0x00   amountOutMin
0x20   path_offset (0x80)
0x40   to
0x60   deadline
0x80   path size <--- offset of path
0xA0   path[0]
...