Debugging Cloe

Debugging is part of development, and unless you’re the perfect developer, you will probably want to do this from time to time. This section contains a few tips for debugging Cloe components and Cloe as a system.

Note

It is recommended you understand how cloe-launch works before reading this section. The document on testing cloe is also useful in the context.

Conan Profiles

You can manage multiple Conan profiles in the ~/.conan/profiles/ directory. The default profile that is used can be configured in ~/.conan/conan.conf.

A profile looks like this:

[settings]
os=Linux
os_build=Linux
arch=x86_64
arch_build=x86_64
compiler=gcc
compiler.version=10
compiler.libcxx=libstdc++11
build_type=RelWithDebInfo
[options]
[build_requires]
[env]
CC=/usr/bin/gcc-10
CXX=/usr/bin/g++-10

You can set the build_type setting to something that CMake understands, such as Release, Debug, or RelWithDebInfo. It is generally recommended to use the RelWithDebInfo, as this mode strikes a balance between optimization and debugging information.

If you set this to Debug, you’ll find that Conan suddenly starts to rebuild all dependencies the next time you build your project. You can avoid this by using a little trick:

build_type=RelWithDebInfo
*@cloe/develop:build_type=Debug

Logging

Start the Cloe runtime with the -l <logging-level> parameter to specify the logging level that should be used. For example:

# cloe-engine -l debug run tests/config_vtd_smoketest

The following log levels are understood: trace, debug, info, warn, error, and critical.

Using GDB

First of all, make sure you have an up-to-date version of GDB. This is especially relevant when using a more recent version of GCC than the Ubuntu version you are using is shipped with:

# sudo apt-get remove gdb
# sudo add-apt-repository ppa:ubuntu-toolchain-r/test
# sudo apt-get update
# sudo apt-get install --install-suggests gcc-9 g++-9 gdb

Then for compiling the project you should compile with the latest version of GCC so that it plays well with GDB. You need to set this in your Conan profile, as seen in the previous section on Conan profiles.

Using GDB with cloe-launch

When directly starting a simulation with cloe-launch exec, you can provide the --debug argument to start GDB with the arguments automatically set to the ones passed through cloe-launch:

# cloe-launch exec -d -P tests/conanfile_default.py -- run tests/config_nop_smoketest.json

You will be dropped in a GDB shell, where you can set your breakpoints as usual, and then to start debugging the program, just type run.

Scripting with GDB

GDB is great, but it can be a bit arcane at times. One solution that often works is to use a competent IDE like Visual Studio Code, but this doesn’t always work, for example when you are debugging within a container. GDB can be automated however, and this brings it to a complete new level: now your debugging sessions can be fully programmed.

For example, given the following contents in a file debug.gdb:

# vim: set ft=gdb:

# Skip asking for confirmation.
set breakpoint pending on

# Ensure that we are actually passing the configurations into the factory.
break vtd::VtdFactory::apply_config
commands 1
   printf "VtdFactory\n"
   printf "-- c.root: %s\n", c.root_.c_str()
   continue
end

# Check what the VtdConfiguration is when we initialize a Vtd.
# We expect that: setup = "Cloe.noGUInoIG"
break vtd::VtdBinding::VtdBinding
commands 2
   p config
end

# Run the program
run -l debug run optional/vtd/tests/test_vtd_smoketest.json

We can then run this script inside a Cloe shell (cloe-launch shell -P optional/vtd/tests/default_profile.py) with:

# gdb --command=debug.gdb cloe-engine

And presto! We’re back in business!