Skip to content

Compilation Overview

zksolc is the compiler ZKsync uses to convert solidity code to zkEVM-compatible bytecode. It uses the same input format as solc but the output bytecodes and their respective hashes. Internally, it uses a custom-compiled solc

Dual Compilation

To allow switching back and forth between EVM and zkEVM as defined in the Execution Overview, we compile the same contract with solc and zksolc. This dual-compiled contract can then be freely translated between both environments as needed. As such, every contract in Foundry ZKsync always has two bytecodes attached - EVM bytecode and zkEVM bytecode, which are not equivalent.

Limitations

See Compilation Limitations.

Compiler Support Policy

To provide clarity and a consistent user experience, Foundry-ZKsync follows a formal zksolc version support policy. This policy ensures compatibility, minimizes user confusion, and addresses issues related to deprecated or unsupported compiler versions.

Supported Versions

  • Foundry officially supports zksolc starting from v1.5.6:
    • v1.5.6: Serves as a baseline with structural compatibility.
    • v1.5.7 and later: Includes support for post-compile-time linkage and subsequent improvements.
    • Note: v1.5.9 is not supported due to a breaking change where AssemblyCreate was introduced as an ErrorType rather than a WarningType. Users should upgrade to v1.5.10 or later to resolve this issue.

Deprecation Policy

  • Backward compatibility will be maintained for supported versions (v1.5.6 and later) unless deprecated due to critical issues (e.g., security vulnerabilities or obsolete functionality).
  • Versions earlier than v1.5.6 and v1.5.9 will not be supported. Compilation with these versions will fail.

Behavior for Unsupported Versions

  • Explicitly Specified Versions: If an unsupported version (e.g., zksolc = 1.5.5) is specified, compilation will fail with a clear error message.
  • Hardcoded Paths: If an unsupported version is used via a hardcoded path (e.g., zksolc = "path/to/zksolc-v1.5.5"), Foundry will emit a warning to inform users without halting compilation.