Inter-contract calls

https://github.com/RareSkills/Udemy-Yul-Code/blob/main/Video-12-13-External-Calls.sol

The hex data field in a transaction is tx.data, or msg.data

when sending to a wallet, you don't have to put any data, unless you are trying to send that person a message (try hackers and taunts1)
you can send a transaction with no value, just a message in the hex field

solidity expects the bytes after the function selector to always be a multiple of 32 in length, but this is convention.
if you send more bytes, solidity will ignore them
But a Yul contract can be programmed to respond to arbitrary length tx.data in an arbitrary manner

Example of txn data:

1st four bytes are fn selector,
concatenated to it is the first argument
addresses have 20 bytes, but abi encoded data is always a multiple of 32 bytes, the address is left padded with zeros

first 4 bytes is fn selector
next 32 bytes is the first argument: left padded with zeros, since address takes 20 bytes
next 32 bytes is the 2nd argument: left padded with zeros, with inte

It doesn't matter if the fn argument was a uint256 or uint128, etc, the abi encoded data will always be 32 bytes

Staticcall

Parameters for staticcall:

how much gas to send -> gas()
- means we are passing all remaining gas to it.
- can hardcode for a specific smaller amount. useful if you worry about DoS
address of contract we are calling: _a
intended txn.data: region in memory -> 28, 32
region in memory to copy results into: 0x00 to 0x20
- when the fn returns, it will overwrite the area containing the address param, but that's fine, since we don't need it anymore

If we pass, a = 7, b = [1,2,3], c = 9, this is what the calldata will look like:

Last updated 2 years ago