waf: make --asan work with gcc

[shine-mild]

Summary

./waf configure --board sitl --debug --asan currently only works with clang. With gcc the build fails in two places; this PR makes the gcc path work.

1. Link flags (Tools/ardupilotwaf/boards.py): -fsanitize=address was added to LINKFLAGS only when clang++ was the compiler, so with gcc every object is instrumented and the final link fails with hundreds of undefined reference to '__asan_report_load8' etc. Add the flag whenever --asan is given.
2. RCProtocolTest frame-size check: ASan redzones inflate stack frames, so the example's -Wframe-larger-than=2000 pragma fails (-Werror, frame becomes ~3040 bytes). Skip the check when __SANITIZE_ADDRESS__ is defined. (The equivalent EKF check is already limited to ChibiOS on master, so no change is needed there.)

The --asan help text already says clang is required; with these changes gcc 15 builds and runs arducopter, examples/RCProtocolTest and tests/test_gsof with ASan instrumentation.

Note

Example/test binaries (APM_BUILD_UNKNOWN) still trip UBSan's null check at startup via AP_Vehicle& vehicle = *AP_Vehicle::get_singleton(); (AP_Vehicle.cpp:305) when --ubsan-abort is also enabled. That is unrelated to ASan and left for a separate change; -fno-sanitize=null is a local workaround.

Testing

CC=gcc CXX=g++ ./waf configure --board sitl --debug --asan --ubsan-abort && ./waf copter --target examples/RCProtocolTest,tests/test_gsof on Ubuntu 26.04 / gcc 15.2: links and runs; a deliberate stack overflow test program confirms the ASan runtime is active.

🤖 Generated with Claude Code

[khancyr]

Looks good.
Test change don't impact flight code so no worries on this.

if asan is now working with gcc we need to remove the comment on g.add_option('--asan') that state that is for clang.

I was able to build copter with gcc 15 and gcc 13 and asan but not running it :

╰─$ /home/pierre/Workspace/ardupilot/ardupilot/build/sitl/bin/arducopter --model + --speedup 1 --slave 0 --sim-address=127.0.0.1 -I0
Setting SIM_SPEEDUP=1.000000
../../libraries/AP_Param/AP_Param.cpp:1508:32: runtime error: 65535 is outside the range of representable values of type 'short int'

So I would say to just remove the config comment and we should be able to use this ! Thanks

[khancyr]

collide with #33976

[shine-mild]

Thanks for the review. Updated the --asan help text to say gcc or clang both work (force-pushed).

The runtime error you hit (AP_Param.cpp: 65535 is outside the range of representable values of type 'short int') is the SITL relay-mask default going through a float into an AP_Int16; the fix for that is in #34778 together with a SoftSerial shift UB. With both applied, SITL starts and runs under --asan --ubsan-abort with gcc 15 here.

On the overlap with #33976: that PR carries the same link-flag change plus the C-side instrumentation and lsan symbol handling, which is more complete. I'm happy to drop the boards.py hunk here and keep only the RCProtocolTest frame-size guard if #33976 is going to land first, or close this one entirely if you'd prefer to take it all through #33976.

[github-actions]

Global Size Summary (Total Flash delta in bytes)

Built from 4d6589e rebased onto b032bcb

Board	Periph	tracker	blimp	bootloader	copter	heli	iofw	plane	rover	sub
DrotekP3Pro	_	_	_	*	_	_	_	_	_	_
Durandal	_	*	*	_	*	*	_	*	*	*
Hitec-Airspeed	*	_	_	_	_	_	_	_	_	_
KakuteF7	_	*	*	_	*	*	_	*	*	*
MambaH743v4	_	*	*	_	*	*	_	*	*	*
MatekF405-CAN	_	_	_	*	_	_	_	_	_	_
MatekF405	_	*	*	_	*	*	_	*	*	*
MatekH743-bdshot	_	*	*	_	*	*	_	*	*	*
Pixhawk1-1M	_	*	*	_	*	*	_	*	*	*
disco	_	*	*	_	*	*	_	*	*	*
f103-GPS	*	_	_	_	_	_	_	_	_	_

[shine-mild]

Closing: #33976 has been merged and master now carries all of this (the gcc link flag, the __SANITIZE_ADDRESS__ guard in RCProtocolTest and the updated --asan help text). Thanks for the review, @khancyr.