获取带有程序集的delegatecall的返回值

Question

我有一份合同a和一份合同B。

合同A声明此功能：

function getIntValue() constant returns (uint);

delegatecall合同A与B的getIntValue函数的适当汇编代码是什么？我对组装还不是很有经验，所以到目前为止我只有这个不起作用：

function getContractAIntValue() constant returns (uint c) {
address addr = address(contractA); // contract A is stored in B.
bytes4 sig = bytes4(sha3("getIntValue()")); // function signature
assembly {
let x := mload(0x40) // find empty storage location using "free memory pointer"
mstore(x,sig) // attach function signature
let status := delegatecall(sub(gas, 10000), addr, add(x, 0x04), 0, x, 0x20)
jumpi(invalidJumpLabel, iszero(status)) // error out if unsuccessful delegatecall
c := mload(x)
}
}

Answer 1

也许你已经解决了它，因为一年多前就有人问过了，但万一有人还在找…

address addr = address(contractA); // contract A is stored in B.
bytes memory sig = abi.encodeWithSignature("getIntValue()"); // function signature
// solium-disable-next-line security/no-inline-assembly
assembly {
let result := delegatecall(sub(gas, 10000), addr, add(sig, 0x20), mload(sig), 0, 0)
let size := returndatasize
let ptr := mload(0x40)
returndatacopy(ptr, 0, size)
// revert instead of invalid() bc if the underlying call failed with invalid() it already wasted gas.
// if the call returned error data, forward it
switch result case 0 { revert(ptr, size) }
default { return(ptr, size) }
}