UBSANOPTIONS

UBSANOPTIONS refers to the configuration string used to control the Undefined Behavior Sanitizer (UBSan) in the LLVM/Clang toolchain. UBSan is a runtime instrumenter that detects various kinds of undefined behavior in program execution. The options can be supplied to the sanitizer via an environment variable—commonly named UBSAN_OPTIONS—and, in some contexts, users refer to the option string as UBSANOPTIONS.

The configuration is expressed as a list of key=value pairs that modify how UBSan reports and handles errors. Pairs are separated by commas (or, on some platforms, colons), and the overall effect is to tune runtime behavior without changing the instrumented code. Typical purposes include enabling or disabling reporting details, controlling whether a program aborts on detection, and selecting the level of output.

Common practical use cases include enabling stack traces on errors to aid debugging and deciding whether the sanitizer should terminate the program immediately or continue running after an error. The exact set of available keys depends on the version of UBSan and the platform, but examples often involve toggling stack traces, error handling, and the verbosity of the emitted messages.

UBSan_OPTIONS is most commonly used when building or running code compiled with -fsanitize=undefined. It provides a flexible runtime knob for developers to tailor diagnostics to their debugging and testing needs. If the variable is not set, UBSan applies its default behavior.

See also: Undefined Behavior Sanitizer (UBSan), Clang/LLVM sanitizers, -fsanitize=undefined, runtime diagnostics.