Low level call is a call to an address directly.
address.call()
while a higher level/contract call, which is a call through solidity, being a higher level language
contract.functionName()
So as it suggests, the higher level call goes through a lot of validation mechanism due to solidity, both post and pre call.
Contract: Since the EVM is a stack based machine, the call is picked at the top and the response inserted at the bottom, Solidity picks up the response from the EVM, and reads the response and reverts if the result is false, and reverts with the intended message.
LowLevel: The call opcode does not throw an exceptions, it just returns a response, which the developer has to handle. https://github.com/ethereum/go-ethereum/blob/a840e9b59f28427d3c65de9f028853e075438201/core/vm/evm.go#L172.
func (evm *EVM) Call(...) (ret []byte, leftOverGas uint64, err error) {
It just returns data “ret”, leftOverGas from execution and err, which indicates a success or fail.
Everything else being equal, the actual call to a contract code happens here
code := evm.resolveCode(addr)
if len(code) == 0 {
ret, err = nil, nil // gas is unchanged
} else {
addrCopy := addr
// If the account has no code, we can abort here
// The depth-check is already done, and precompiles handled above
contract := NewContract(caller, AccountRef(addrCopy), value, gas)
contract.SetCallCode(&addrCopy, evm.resolveCodeHash(addrCopy), code)
ret, err = evm.interpreter.Run(contract, input, false)
gas = contract.Gas
}
The return data from the returned execution is stored in ret, and err contains the success response, with nil indicating no error and a custom error response indicating error type.