LLVMFuzzerTestOneInput

LLVMFuzzerTestOneInput is a function that serves as the primary entry point for libFuzzer, a coverage-guided fuzzing engine developed by the LLVM Project. When libFuzzer is used to fuzz a target program, it repeatedly calls this function, providing it with synthesized input data. The purpose of LLVMFuzzerTestOneInput is to consume this input and execute the code being fuzzed.

The signature of the LLVMFuzzerTestOneInput function is typically void LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size). The first argument, Data, is a pointer to the generated input, and Size specifies the length of that input in bytes. The fuzzer framework automatically manages the generation and provision of this data.

Developers are responsible for implementing LLVMFuzzerTestOneInput within their fuzzing target. Inside this function, they should parse the provided Data and then call the specific API, function, or code path they wish to test. The goal is to trigger unexpected behavior, crashes, or assertion failures within the target code, which can indicate security vulnerabilities or bugs.

libFuzzer then monitors the execution of LLVMFuzzerTestOneInput for various outcomes. If a crash occurs, it saves the input that caused it. If the input leads to new code coverage, libFuzzer will prioritize that input for future fuzzing iterations, effectively guiding the fuzzing process towards more interesting and potentially buggy parts of the code. The simplicity of the LLVMFuzzerTestOneInput interface makes it straightforward for developers to integrate fuzzing into their projects.