The input data for a function call is assumed to be in the format defined by the ABI
specification <ABI>. Among others, the ABI specification requires arguments to be padded to multiples of 32 bytes. The internal function calls use a different convention.
Arguments for the constructor of a contract are directly appended at the end of the contract's code, also in ABI encoding. The constructor will access them through a hard-coded offset, and not by using the codesize opcode, since this of course changes when appending data to the code.