Sanitizers

Sanitizers are compiler-instrumentation tools that detect whole classes of bugs at runtime. PX4 can build SITL with them to catch problems that are otherwise hard to reproduce:

• AddressSanitizer (ASan) — out-of-bounds accesses, use-after-free, memory leaks.
• ThreadSanitizer (TSan) — data races and lock-order inversions.
• MemorySanitizer (MSan) — reads of uninitialized memory (Clang only).
• UndefinedBehaviorSanitizer (UBSan) — undefined behaviour (signed overflow, misaligned access, …).

INFO

Sanitizers are only available for POSIX/SITL builds, where the host compiler instruments the code. They are not used on the NuttX flight-controller targets.

Building and running

Set the matching environment variable when building SITL. It selects the corresponding CMAKE_BUILD_TYPE:

Variable	Sanitizer
PX4_ASAN	AddressSanitizer
PX4_TSAN	ThreadSanitizer
PX4_MSAN	MemorySanitizer
PX4_UBSAN	UndefinedBehaviorSanitizer

For example, to build and run SITL under ThreadSanitizer:

PX4_TSAN=1 make px4_sitl_default

To build and run the unit and integration test suite under a sanitizer:

PX4_TSAN=1 make tests

WARNING

A sanitizer is a distinct CMAKE_BUILD_TYPE, so switching to or from one rebuilds from scratch. Sanitized binaries are larger and run several times slower (ASan/TSan roughly 2–5×), and lockstep timing changes, so expect tests to take longer.

Linux: ASLR fix

On recent Linux kernels the default address-space-layout randomization entropy is too high for the sanitizer runtimes' shadow-memory mapping, and the process aborts at startup with e.g.:

FATAL: ThreadSanitizer: unexpected memory mapping 0x... - 0x...

Lower the mmap randomization (needed for both ASan and TSan), once per boot:

sudo sysctl vm.mmap_rnd_bits=28

To make it persistent across reboots:

echo 'vm.mmap_rnd_bits=28' | sudo tee /etc/sysctl.d/99-sanitizers.conf

If 28 still fails on your kernel, try 26.

ThreadSanitizer suppressions

Running SITL with the Gazebo bridge under TSan reports many data races inside the third-party simulation transport (ZeroMQ and gz-transport) and the PX4↔Gazebo bridge glue. None of this is in the flight code path or the SIH-based CI, and it can't be fixed here, so it is filtered with a suppressions file at test/sitl_tsan.supp:

TSAN_OPTIONS="suppressions=$PWD/test/sitl_tsan.supp" PX4_TSAN=1 make px4_sitl_default gz_x500

WARNING

Only add third-party / simulation symbols to the suppressions file — never flight-code symbols. A race detector is only useful at zero reports; suppressing your own code blinds it to real bugs.