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tech 14 August 2026

Towards a Safe Rust FFI with Fil-C

Explore how Fil-C can revolutionize interoperability between Rust and C, offering enhanced memory safety without sacrificing performance.

Article inspired by the original source
I want extern "fil-c" ↗ domenkozar.com

Introduction

Rust is renowned for its compile-time memory safety, providing developers with a reliable environment to build secure software. However, when Rust needs to interact with C libraries via the FFI (Foreign Function Interface), this guarantee can be compromised. This is where Fil-C comes into play, redefining the rules of this interoperability.

The Current Interoperability Issue

Currently, Rust's FFI with C relies on implicit trust in C libraries to uphold safety contracts, which can be risky. Security vulnerabilities in C are well-documented, and a simple mistake can lead to severe exploits. Rewriting these libraries in Rust is often costly and unrealistic in terms of resources.

Fil-C: A New Approach

Fil-C offers an innovative solution by recompiling C and C++ code to include capability checks and a concurrent garbage collector. Instead of allowing memory safety violations, these lead to panics, thereby making the code safer without requiring major source code changes.

Integrating Fil-C with Rust

The idea is to create a Rust FFI that directly speaks the Fil-C ABI (Application Binary Interface). This integration would allow Rust to continue using its memory safety guarantees while interacting with C code via Fil-C. The first step would be to handle scalar values, copied strings, and opaque handles, while generating safe Rust wrappers.

Current State of the Technology

Filnix, a project making Fil-C compatible with Nix, paves the way by providing a robust cross-compilation platform. With over 100 nixpkgs packages ported, filnix offers a testable and reproducible environment for developing a Rust-Fil-C bridge.

Comparison with Zig

Zig, another programming language, proposes a similar approach with an ABI inspired by Fil-C, proving that the idea has real potential. By adding runtime memory safety to the entire C and C++ dependency tree, Zig aims to offer a secure alternative that could well align with the goals of the Rust-Fil-C bridge.

Impact on Software Development

Adopting Fil-C in the Rust ecosystem could transform how developers approach interoperability. Legacy libraries could be used without fear of security flaws, while offering the possibility to rewrite critical parts in Rust to eliminate runtime checks.

Conclusion

Fil-C offers a promising path to secure interoperability between Rust and C, without sacrificing performance. As the technology continues to develop, it could well become a standard in software development.

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Rust Fil-C FFI interopérabilité sécurité mémoire
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