This repo contains a version of clang that is being modified to support Checked C. Checked C is an extension to C that adds checking to detect or prevent common programming errors such as out-of-bounds memory accesses. The Checked C specification is available at the Checked C repo.

The code for the Checked C version of LLVM/clang lives in two repos: the Checked C clang repo and the Checked C LLVM repo. Each repo is licensed under the University of Illinois/NCSA license. The tests for Checked C live in the Checked C repo. These are language conformance tests, so they are placed with the specification, not the compiler. The test code is licensed under the MIT license. See the file LICENSE.TXT in each repo for complete details of licensing.

We are close to having a complete implementation of the new _Ptr types and the language features for using them. We also have support for parsing and typechecking bounds expressions and bounds declarations. We are working on interoperation support now. To able to use the Checked C extension in existing code bases, we need the interoperation support, so we are implementing it before other features.

We have:

• Extended LLVM/clang with a feature flag -fcheckedc-extension. This flag is valid only for C programs. It cannot be used with C++, Objective C, or OpenCL.
• Implemented parsing and typechecking for the new _Ptr, _Array_ptr, and _Checked array types, including implicit conversions described in the Checked C specification. The _Array_ptr and _Checked array types do not have any runtime bounds checking yet.
• Implemented parsing and typechecking for bounds expression and in-line bounds declarations.
• Implemented parsing and typechecking for bounds-safe interfaces, including the implicit conversions done at bounds-safe interfaces.

We are now:

• Implementing function types with bounds information.
• Implementing type checking of redeclarations of variables and functions with bounds information. When this is finished, interoperation support will be mostly done. Programmers will be able to redeclare existing variables and functions with additional bounds information.

After that, we will begin implementing static semantics checking for programs that use _Ptr pointers and _Array_ptr pointers to constant-sized data. This includes

• Checking the correctness of bounds declarations for constant-sized data.
• Checking that casts to _Ptr types from _Array_ptr types are bounds-safe.

Programmers are welcome to ``kick the tires'' on Checked C as it is being implemented. You will have to build your own copy of the compiler for now:

• Setup and Build describes the organization of the code, how to set up a development machine to build clang, and how to build clang.
• Testing describes how to test the compiler once you have built it.
• The Implementation Notes describe the implementation of Checked C in LLVM\clang.

We welcome contributions to the Checked C project. To get involved in the project, see Contributing to Checked C. We have a wish list of possible projects there.

For code contributions, we follow the standard Github workflow. See Contributing to Checked C for more detail. You will need to sign a contributor license agreement before contributing code.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.