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c++emacsgdbbazel

C++ debugging with gdb & bazel (& emacs)

I want to debug an executable generated with Bazel. The gdb debugger is lost with the links generated by Bazel and is not able to show me the C++ source code. How to fix that?

The project root directory is /home/.../Cpp/

./Cpp/
├── bazel-bin -> /home/picaud/.cache/bazel/_bazel_picaud...
├── bazel-Cpp -> /home/picaud/.cache/bazel/_bazel_picaud...
├── bazel-genfiles -> /home/picaud/.cache/bazel/_bazel_picaud...  
├── bazel-out -> /home/picaud/.cache/bazel/_bazel_picaud...   
├── bin
│   ├── BUILD
│   └── main.cpp
├── MyLib
│   ├── BUILD
│   ├── ....hpp
│   ├──  ...cpp
└── WORKSPACE
Solution

  • The first step is to generate executables using the debug mode:

    bazel build ... --compilation_mode=dbg --subcommands

    (the --subcommands option is not mandatory it only shows the executed commands, you can remove it if you want)

    gdb debugging from the command line:

    You can start gdb with this command (from your project root directory):

    gdbtui bazel-bin/bin/main

    -> everything is okay, you should see your C++ source code.

    The error would be to do:

    cd bazel-bin/bin/
gdbtui main

    In that case, because of the links, gdb is not able to retrieve the source code.

    gdb debugging from Emacs:

    Do as usual

    M-x gdb

    In the emacs prompt define the complete absolute path to the executable:

    gdb -i=mi /home/picaud/.../Cpp/bazel-bin/bin/main

    Now in the gdb buffer you must tell gdb where to find source by defining your absolute path to the project root directory (where your WORKSPACE file is):

    set directories /home/picaud/.../Cpp

    Now the emacs gdb command should work properly and you can debug as usual.

    (well this was an easy fix, just a note that maybe can help...)