{Solidity:​log}

Posted by Solidity Team on December 5, 2022

More than two years have passed since we introduced Solidity core team members on the blog and we realized it is high time for some updates: Meet new team members, find out who moved on to other adventures and learn about recent changes in the team structure! Before we dive in, a reminder that the Solidity programming language and compiler are open-source community projects. This post dives into the core team that leads the development. Nevertheless, we cannot stress enough how...

Posted by Solidity Team on September 8, 2022

On September 5, 2022, a bug in Solidity's Yul optimizer was found by differential fuzzing. The bug was introduced in version 0.8.13 and Solidity version 0.8.17, released on September 08, 2022, provides a fix. The bug is significantly easier to trigger with optimized via-IR code generation, but can theoretically also occur in optimized legacy code generation. We assigned the bug a severity of "medium/high". Who Should Be Concerned If you're using optimized legacy code generation, you only need to be concerned, if you use...

Posted by Solidity Team on September 8, 2022

Solidity v0.8.17 fixes an important bug, makes overflow checks on multiplication more efficient and adds an LSP feature to always analyze all files in a project. Important Bugs Storage Write Removal Bug On Conditional Early Termination The bug may result in storage writes being incorrectly considered redundant and removed by the optimizer. The problem manifests in presence of assembly functions that may conditionally terminate the external EVM call using the return() or stop() opcode. See the security alert post on Storage Write Removal Bug On Conditional Early Termination for...

Posted by Solidity Team on August 8, 2022

Solidity v0.8.16 fixes an important bug. The bug may result in small parts of dynamic tuple components being inadvertently zeroed during ABI re-encoding when the last component is a statically-sized uint or bytes32 calldata array. See Head Overflow Bug in Calldata Tuple ABI-Reencoding for more information. Apart from that, there are several minor bug fixes and improvements like more gas-efficient overflow checks for addition and subtraction. Full Changelog Important Bugfixes: Code Generation: Fix data corruption that affected ABI-encoding of calldata values represented by tuples: structs at any nesting level; argument...

Posted by Solidity Team on August 8, 2022

On July 5, 2022, Chance Hudson (@vimwitch) from the Ethereum Foundation discovered a bug in the Solidity code generator. The earliest affected version of the compiler is 0.5.8, which introduced ABI-reencoding of calldata arrays and structs. Solidity version 0.8.16, released on August 08, 2022, provides a fix. We assigned the bug a severity of "medium". Which Contracts are Affected? The effects of the bug manifest when a contract performs ABI-encoding of a tuple that meets all of the following conditions: The last component of the tuple...

Posted by Solidity Team on June 15, 2022

Solidity v0.8.15 fixes two important bugs, improves inlining heuristics and adds a .selector member for errors and events. Important Bugs The first one is an optimizer bug that can lead to memory write operations in inline assembly being removed if the result of such an operation is not read back from within the same assembly block. The bug can be triggered only when using the default legacy compiler pipeline (the new compilation pipeline via IR is not affected) and happens only in assembly blocks that never...

Posted by Solidity Team on June 15, 2022

On June 5, 2022, John Toman of the Certora development team reported an optimizer bug that can cause memory writes in inline assembly blocks to be incorrectly removed under certain conditions. The bug was introduced in Solidity 0.8.13 with a new Yul optimizer step meant to remove unused writes to memory and storage. We assigned the bug a severity of "medium". Which Contracts are Affected? The Yul optimizer considers all memory writes in the outermost Yul block that are never read from as unused and removes them. This...

Posted by Solidity Team on June 15, 2022

On July 1, 2021, a bug in the Solidity code generator was found by differential fuzzing. The bug causes the legacy code generation pipeline to generate code that may write dirty values to storage when copying bytes arrays from calldata or memory. Initially, it was assumed that the dirty values in storage are only observable using inline assembly. However, resizing a bytes array using an empty .push() without actually writing values to it, can expose the dirty bytes without any use of inline assembly. The bug...

Posted by Solidity Team on May 18, 2022

Solidity v0.8.14 fixes two important bugs. The first one is related to ABI-encoding nested arrays directly from calldata. You can find more information in the blog post. The second bug is triggered in certain inheritance structures and can cause a memory pointer to be interpreted as a calldata pointer or vice-versa. We also have a dedicated blog post about this bug. Apart from these, there are several minor bug fixes and improvements. Please note: Unfortunately, the npm wrapper package of this version is corrupted. Using the new soljson.js...

Posted by Solidity Team on May 17, 2022

On February 5th 2021, Nicolas Venturo reported a bug that allows overriding functions to change the data location of parameters from memory to calldata. The bug was introduced in Solidity 0.6.9 together with the ability to use calldata data location for all variables (and not just parameters of external functions). We assigned the bug a severity of "very low". Which Contracts are Affected? The effect of the bug is that a memory pointer is interpreted as a calldata pointer or vice-versa. It can only happen if you change...