Negative signed integers as indexed event inputs are not decoded correctly

[shoenseiwaso]

System information

Geth version:

$ geth version
Geth
Version: 1.9.6-stable
Git Commit: bd05968077f27f7eb083404dd8448157996a8788
Architecture: amd64
Protocol Versions: [63]
Network Id: 1
Go Version: go1.13.1
Operating System: darwin

OS & Version: macOS 10.14.6

Expected behaviour

Events which emit negative signed integers with size >64 bits are decoded correctly.

Actual behaviour

They are treated as unsigned integers and not decoded correctly.

Steps to reproduce the behaviour

The problem is here:

go-ethereum/accounts/abi/bind/topics.go

Lines 214 to 215 in de2259d

	case abi.IntTy, abi.UintTy:
	num := new(big.Int).SetBytes(topics[0][:])

For integers with size >64 bits, negative values will be encoded by the EVM with a size larger than max(int256). For example, -1 for an int256 (or int192, etc.) is 2^256-1, -2 is 2^256-2, etc.

Non-indexed inputs are decoded correctly via readInteger() in accounts/abi/unpack.go:

go-ethereum/accounts/abi/unpack.go

Lines 56 to 71 in de2259d

	default:
	// the only case lefts for integer is int256/uint256.
	// big.SetBytes can't tell if a number is negative, positive on itself.
	// On EVM, if the returned number > max int256, it is negative.
	ret := new(big.Int).SetBytes(b)
	if typ == UintTy {
	return ret
	}
	if ret.Cmp(maxInt256) > 0 {
	ret.Add(maxUint256, big.NewInt(0).Neg(ret))
	ret.Add(ret, big.NewInt(1))
	ret.Neg(ret)
	}
	return ret
	}

To reproduce:

1. Deploy the following smart contract:

pragma solidity >=0.0.0;

contract TestIntEvents {
    event Int192Event(int192 x);
    event Int192EventIndexed(int192 indexed x);


    function send192(int192 x) public {
        emit Int192Event(x);
    }

    function send192Indexed(int192 x) public {
        emit Int192EventIndexed(x);
    }
}

2. Try calling send192(-1) and send192Indexed(-1).
3. Observe the values returned from both events via go-ethereum:

Int192Event(-1)
// Ok

Int192EventIndexed(115792089237316195423570985008687907853269984665640564039457584007913129639935)
// Not Ok! Expected -1