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Checker Developer Manual

The static analyzer engine performs symbolic execution of the program and relies on a set of checkers to implement the logic for detecting and constructing bug reports. This page provides hints and guidelines for anyone who is interested in implementing their own checker. The static analyzer is a part of the Clang project, so consult Hacking on Clang and LLVM Programmer's Manual for general developer guidelines and information.

Getting Started

Static Analyzer Overview

The analyzer core performs symbolic execution of the given program. All the input values are represented with symbolic values; further, the engine deduces the values of all the expressions in the program based on the input symbols and the path. The execution is path sensitive and every possible path through the program is explored. The explored execution traces are represented with ExplidedGraph object. Each node of the graph is ExplodedNode, which consists of a ProgramPoint and a ProgramState.

ProgramPoint represents the corresponding location in the program (or the CFG graph). ProgramPoint is also used to record additional information on when/how the state was added. For example, PostPurgeDeadSymbolsKind kind means that the state is the result of purging dead symbols - the analyzer's equivalent of garbage collection.

ProgramState represents abstract state of the program. It consists of:

Checkers are not merely passive receivers of the analyzer core changes - they actively participate in the ProgramState construction through the GenericDataMap which can be used to store the checker-defined part of the state. Each time the analyzer engine explores a new statement, it notifies each checker registered to listen for that statement, giving it an opportunity to either report a bug or modify the state. (As a rule of thumb, the checker itself should be stateless.) The checkers are called one after another in the predefined order; thus, calling all the checkers adds a chain to the ExplodedGraph.

Idea for a Checker

Here are several questions which you should consider when evaluating your checker idea:

Checker Registration

All checker implementation files are located in clang/lib/StaticAnalyzer/Checkers folder. Follow the steps below to register a new checker with the analyzer.
  1. Create a new checker implementation file, for example ./lib/StaticAnalyzer/Checkers/NewChecker.cpp 
    using namespace clang;
using namespace ento;

namespace {
class NewChecker: public Checker< check::PreStmt > {
public:
  void checkPreStmt(const CallExpr *CE, CheckerContext &Ctx) const {}
}
}
void ento::registerNewChecker(CheckerManager &mgr) {
  mgr.registerChecker();
}
  2. Pick the package name for your checker and add the registration code to ./lib/StaticAnalyzer/Checkers/Checkers.td. Note, all checkers should first be developed as experimental. Suppose our new checker performs security related checks, then we should add the following lines under SecurityExperimental package: 
    let ParentPackage = SecurityExperimental in {
...
def NewChecker : Checker<"NewChecker">,
  HelpText<"This text should give a short description of the checks performed.">,
  DescFile<"NewChecker.cpp">;
...
} // end "security.experimental"
  3. Make the source code file visible to CMake by adding it to ./lib/StaticAnalyzer/Checkers/CMakeLists.txt.
  4. Compile and see your checker in the list of available checkers by running:
    $clang -cc1 -analyzer-checker-help

Checker Skeleton

There are two main decisions you need to make:

Bug Reports

AST Visitors

Some checks might not require path-sensitivity to be effective. Simple AST walk might be sufficient. If that is the case, consider implementing a Clang compiler warning. On the other hand, a check might not be acceptable as a compiler warning; for example, because of a relatively high false positive rate. In this situation, AST callbacks checkASTDecl and checkASTCodeBody are your best friends.

Testing

Every patch should be well tested with Clang regression tests. The checker tests live in clang/test/Analysis folder. To run all of the analyzer tests, execute the following from the clang build directory: 
    $ TESTDIRS=Analysis make test

Useful Commands/Debugging Hints