fsanitizeaddress

fsanitizeaddress is the compiler option -fsanitize=address used to enable AddressSanitizer, a runtime memory error detector included in the Clang/LLVM toolchain and supported by GCC in compatible versions. It instruments C and C++ programs to find a range of memory corruption bugs, including heap- and stack-based buffer overflows, use-after-free, use-after-return, and double-free, by reporting errors when a forbidden memory access occurs.

AddressSanitizer works by instrumenting code and using a separate shadow memory to track the state of application memory. Each region of user memory has a corresponding shadow byte that encodes whether the area is addressable, red zones, or freed. The instrumented code checks every memory access against this shadow memory and raises an error if an access is invalid. A runtime library (libasan) handles reporting, aborting on errors, and producing diagnostics such as stack traces, the faulty access, and allocation/deallocation points. The approach typically incurs noticeable performance and memory overhead during execution.

Usage and limitations: The flag is usually combined with -g for debugging information and with -O1 or higher, sometimes with -fno-omit-frame-pointer. It is most effective when the program is built with debugging symbols and run under representative workloads. It may not be fully compatible with all platforms, third-party libraries, or code loaded dynamically, and can produce false positives in rare environments. It is intended for development and testing rather than production deployment.

Output and interpretation: When a bug is detected, AddressSanitizer prints a diagnostic message indicating the error type (for example, heap-buffer-overflow or use-after-free), a stack trace, and details about the allocation and deallocation sites. This information helps locate the bug and reproduce it with failing input.