# Simulation Debugging

As the simulation is running on the host machine, all the desktop development tools are available.

# CLANG Address Sanitizer (Mac OS, Linux)

The Clang address sanitizer can help to find alignment (bus) errors and other memory faults like segmentation faults. The command below sets the right compile options.

make clean # only required on first address sanitizer run after a normal build
PX4_ASAN=1 make px4_sitl jmavsim

# Valgrind

brew install valgrind

or

sudo apt-get install valgrind

To use valgrind during the SITL simulation:

make px4_sitl_default jmavsim___valgrind

# Launch Gazebo Classic SITL Without Debugger

By default SITL is launched without a debugger attached when using any simulator backend:

make px4_sitl_default gz
make px4_sitl_default gazebo-classic
make px4_sitl_default jmavsim

For Gazebo Classic (only) you can also start the simulator with a debugger attached. Note however, that you must provide the vehicle type in the simulator target, as shown below:

make px4_sitl_default gazebo-classic_iris_gdb
make px4_sitl_default gazebo-classic_iris_lldb

This will start the debugger and launch the SITL application with Gazebo and the Iris simulator. In order to break into the debugger shell and halt the execution, hit CTRL-C:

Process 16529 stopped
* thread #1: tid = 0x114e6d, 0x00007fff90f4430a libsystem_kernel.dylib`__read_nocancel + 10, name = 'px4', queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
    frame #0: 0x00007fff90f4430a libsystem_kernel.dylib`__read_nocancel + 10
libsystem_kernel.dylib`__read_nocancel:
->  0x7fff90f4430a <+10>: jae    0x7fff90f44314            ; <+20>
    0x7fff90f4430c <+12>: movq   %rax, %rdi
    0x7fff90f4430f <+15>: jmp    0x7fff90f3fc53            ; cerror_nocancel
    0x7fff90f44314 <+20>: retq
(lldb)

In order to not have the DriverFrameworks scheduling interfere with the debugging session SIGCONT should be masked in LLDB and GDB:

(lldb) process handle SIGCONT -n false -p false -s false

Or in the case of GDB:

(gdb) handle SIGCONT noprint nostop

After that the lldb or gdb shells behave like normal sessions, please refer to the LLDB / GDB documentation.

The last parameter, the <viewer_model_debugger> triplet, is actually passed to make in the build directory, so

make px4_sitl_default gazebo-classic_iris_gdb

is equivalent with

make px4_sitl_default	# Configure with cmake
make -C build/px4_sitl_default classic_iris_gdb

A full list of the available make targets in the build directory can be obtained with:

make help

# Attaching GDB to running SITL

You can also start your simulation, and then attach gdb:

  1. In one terminal screen enter the command to start your simulation:

    make px4_sitl_default gazebo-classic
    

    As the script runs, note the SITL COMMAND: output text located right above the large "PX4" text. It will list the location of your px4 bin file for later use.

    SITL COMMAND: "<px4 bin file>" "<build dir>"/etc
    
    ______  __   __    ___
    | ___ \ \ \ / /   /   |
    | |_/ /  \ V /   / /| |
    |  __/   /   \  / /_| |
    | |     / /^\ \ \___  |
    \_|     \/   \/     |_/
    
    px4 starting.
    
    INFO  [px4] startup script: /bin/sh etc/init.d-posix/rcS 0
    INFO  [init] found model autostart file as SYS_AUTOSTART=10015
    
  2. Open another terminal and type:

    ps -a
    

    You will want to note the PID of the process named "PX4"

    (In this example it is 14149)

    atlas:~/px4/main/PX4-Autopilot$ ps -a
        PID TTY          TIME CMD
    1796 tty2     00:01:59 Xorg
    1836 tty2     00:00:00 gnome-session-b
    14027 pts/1    00:00:00 make
    14077 pts/1    00:00:00 sh
    14078 pts/1    00:00:00 cmake
    14079 pts/1    00:00:00 ninja
    14090 pts/1    00:00:00 sh
    14091 pts/1    00:00:00 bash
    14095 pts/1    00:01:23 gzserver
    14149 pts/1    00:02:48 px4
    14808 pts/2    00:00:00 ps
    
  3. Then type in the same window

    sudo gdb [px4 bin file path (from step 1) here]
    

    For example,

    sudo gdb /home/atlas/px4/base/PX4-Autopilot/build/px4_sitl_default/bin/px4
    

    Now, you can attach to the PX4 instance by entering the PID noted in step 2.

    attach [PID on px4]
    

    You should now have a GDB interface to debug with.

# Compiler optimization

It is possible to suppress compiler optimization for given executables and/or modules (as added by cmake with add_executable or add_library) when configuring for posix_sitl_*. This can be handy when it is necessary to step through code with a debugger or print variables that would otherwise be optimized out.

To do so, set the environment variable PX4_NO_OPTIMIZATION to be a semi-colon separated list of regular expressions that match the targets that need to be compiled without optimization. This environment variable is ignored when the configuration isn't posix_sitl_*.

For example,

export PX4_NO_OPTIMIZATION='px4;^modules__uORB;^modules__systemlib$'

would suppress optimization of the targets: platforms__posix__px4_layer, modules__systemlib, modules__uORB, examples__px4_simple_app, modules__uORB__uORB_tests and px4.

The targets that can be matched with these regular expressions can be printed with the command:

make -C build/posix_sitl_* list_cmake_targets