Open code423n4 opened 1 year ago
It can be as high quality report!
2k
2k
100
22 instances, saves roughly 16 gas (jump) + 8 (handle return value 528
80
200 gas (cannot figure out from benchmark so am using guesstimate)
700 because it showed all instances (vs 100 / 200 for less specific reports)
50 each 200
Rest I think is negligible
5808
Great progress!
Have correctly ignored the solidity version finding as the config sets it to .8.17 and the readme clarifies that
GalloDaSballo marked the issue as grade-a
FINDINGS
NB: Some functions have been truncated where neccessary to just show affected parts of the code Throught the report some places might be denoted with audit tags to show the actual place affected.
Pack structs by putting data types that can be packed together next to each other.
As the solidity EVM works with 32 bytes, variables less than 32 bytes should be packed inside a struct so that they can be stored in the same slot, this saves gas when writing to storage ~20000 gas
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/Storage.sol#L69-L105 Save 1 SLOT
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/interfaces/IExecutor.sol#L15-L24
IExecutor.sol.StoredBlockInfo{}: From 7 slots to 6 slots
Cache storage values in memory to minimize SLOADs
The code can be optimized by minimizing the number of SLOADs.
SLOADs are expensive (100 gas after the 1st one) compared to MLOADs/MSTOREs (3 gas each). Storage values read multiple times should instead be cached in memory the first time (costing 1 SLOAD) and then read from this cache to avoid multiple SLOADs.
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Governance.sol#L28-L40
Governance.sol.acceptGovernor(): s.governor should be cached
Internal/Private functions only called once can be inlined to save gas
Not inlining costs 20 to 40 gas because of two extra JUMP instructions and additional stack operations needed for function calls.
Affected code:
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L23-L27
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L89-L90
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L177
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L190
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L274-L279
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L296
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L349
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L354
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L362
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L372
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Executor.sol#L376
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Mailbox.sol#L75
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Mailbox.sol#L116-L123
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Mailbox.sol#L144-L153
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Mailbox.sol#L216-L220
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1ERC20Bridge.sol#L136-L140
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1EthBridge.sol#L113-L122
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/zksync/contracts/bridge/L2ERC20Bridge.sol#L73
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/zksync/contracts/bridge/L2ETHBridge.sol#L74
Multiple accesses of a mapping/array should use a local variable cache
Caching a mapping's value in a local storage or calldata variable when the value is accessed multiple times saves ~42 gas per access due to not having to perform the same offset calculation every time. Help the Optimizer by saving a storage variable's reference instead of repeatedly fetching it
To help the optimizer,declare a storage type variable and use it instead of repeatedly fetching the reference in a map or an array. As an example, instead of repeatedly calling
someMap[someIndex]
, save its reference like this:SomeStruct storage someStruct = someMap[someIndex]
and use it.https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Governance.sol#L45-L50
Governance.sol.setValidator(): s.validators[_validator] should be cached in local storage
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1ERC20Bridge.sol#L225-L257
L1ERC20Bridge.sol.finalizeWithdrawal(): isWithdrawalFinalized[_l2BlockNumber][_l2MessageIndex] should be cached
Use calldata instead of memory for function parameters
If a reference type function parameter is read-only, it is cheaper in gas to use calldata instead of memory. Calldata is a non-modifiable, non-persistent area where function arguments are stored, and behaves mostly like memory.
Note that I've also flagged instances where the function is public but can be marked as external since it's not called by the contract, and cases where a constructor is involved
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/facets/Mailbox.sol#L40-L47
Avoid contract existence checks by using solidity version 0.8.10 or later
Prior to 0.8.10 the compiler inserted extra code, including EXTCODESIZE (100 gas), to check for contract existence for external calls. In more recent solidity versions, the compiler will not insert these checks if the external call has a return value
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1ERC20Bridge.sol#L141
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1EthBridge.sol#L98-L104
Usage of uints/ints smaller than 32 bytes (256 bits) incurs overhead
When using elements that are smaller than 32 bytes, your contract’s gas usage may be higher. This is because the EVM operates on 32 bytes at a time. Therefore, if the element is smaller than that, the EVM must use more operations in order to reduce the size of the element from 32 bytes to the desired size.
https://docs.soliditylang.org/en/v0.8.11/internals/layout_in_storage.html Use a larger size then downcast where needed
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1ERC20Bridge.sol#L179-L187
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1EthBridge.sol#L132-L140
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/common/AllowList.sol#L46-L50
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/DiamondInit.sol#L25-L37
Using unchecked blocks to save gas - Increments in for loop can be unchecked ( save 30-40 gas per loop iteration)
The majority of Solidity for loops increment a uint256 variable that starts at 0. These increment operations never need to be checked for over/underflow because the variable will never reach the max number of uint256 (will run out of gas long before that happens). The default over/underflow check wastes gas in every iteration of virtually every for loop . eg.
e.g Let's work with a sample loop below.
can be written as shown below.
We can also write it as an inlined function like below.
Affected code
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/libraries/Diamond.sol#L94
Other Instances to modify https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/libraries/Diamond.sol#L132
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/libraries/Diamond.sol#L153
https://github.com/code-423n4/2022-10-zksync/blob/4db6c596931a291b17a4e0e2929adf810a4a0eed/ethereum/contracts/zksync/libraries/Diamond.sol#L173
see resource
Splitting require() statements that use && saves gas - (saves 8 gas per &&)
Instead of using the && operator in a single require statement to check multiple conditions,using multiple require statements with 1 condition per require statement will save 8 GAS per && The gas difference would only be realized if the revert condition is realized(met).
Proof The following tests were carried out in remix with both optimization turned on and off
Execution cost 21617 with optimization and using && 21976 without optimization and using &&
After splitting the require statement
Execution cost 21609 with optimization and split require 21968 without optimization and using split require
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/common/AllowList.sol#L96-L101
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/common/L2ContractHelper.sol#L65
Use a more recent version of solidity
Use a solidity version of at least 0.8.2 to get simple compiler automatic inlining Use a solidity version of at least 0.8.3 to get better struct packing and cheaper multiple storage reads Use a solidity version of at least 0.8.4 to get custom errors, which are cheaper at deployment than revert()/require() strings Use a solidity version of at least 0.8.10 to have external calls skip contract existence checks if the external call has a return value
https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/DiamondProxy.sol#L3
All the contracts in scope seems to be using the above version