MSan

MemorySanitizer (MSan) is a dynamic analysis tool in the LLVM project designed to detect reads of uninitialized memory in C and C++ programs. It works by instrumenting the program at compile time and maintaining a parallel shadow memory that encodes the initialization state of each byte of usable memory. Before every memory read, MSan checks the corresponding shadow value and reports an error if the memory being read has not been properly initialized, typically providing a stack trace to help locate the source of the issue.

Origin tracking is an optional feature of MSan. When enabled with flags such as -fsanitize-memory-track-origins, MSan records the origin of uninitialized values, helping developers identify where the uninitialized memory was first written or originated.

Build and usage: programs are compiled with clang using -fsanitize=memory and linked with the MemorySanitizer runtime. Running the instrumented binary will trigger diagnostics at the point of uninitialized reads. For deeper debugging, developers can enable origin tracking to obtain more detailed reports about where the memory was last initialized.

Limitations and scope: MSan is primarily focused on detecting reads of uninitialized memory and does not by itself address other classes of memory-safety bugs such as use-after-free or leaks. It can have substantial performance and memory overhead due to instrumentation and shadow memory. It is commonly used during development and testing rather than in production builds. MSan is part of the LLVM Sanitizers family and is supported on platforms where LLVM tooling is available, with broader support typically on Linux and macOS; Windows support is more experimental.