TierOps Manual Review Findings

TOP-01M: Insufficient Documentation of Stack Layout

Type	Severity	Location
Standard Conformity		TierOps.sol:L36, L91-L94

Description:

The stack layout expected by the various operators in the TierOps contract are insufficiently documented and potentially incorrectly so in the first linked instance which specifies the stack contains the address and ITier contract whereas the opposite layout is expected (ITier and address).

Example:

Copy
35// Stack the report returned by an `ITier` contract.
36// Top two stack vals are used as the address and `ITier` contract
37// to check against.
38if (opcode_ == REPORT) {
39    state_.stackIndex -= 2;
40    baseIndex_ = state_.stackIndex;
41    state_.stack[baseIndex_] = ITier(
42        address(uint160(state_.stack[baseIndex_]))
43    ).report(address(uint160(state_.stack[baseIndex_ + 1])));
44    state_.stackIndex++;
45}

Recommendation:

We advise the expected layout to be properly documented to aid in integrators of the contract whereby the first linked instance is corrected and the second contains a layout of reports as well as the block number to evaluate with at the end of the stack.

Alleviation:

The layout of each instruction is now properly documented in each instruction present in the contract thereby alleviating this exhibit.