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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
Picaud Vincent
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1 Answers1

28

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

bazel build ... --compilation_mode=dbg -s

(the -s 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...)

Picaud Vincent
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    I've tried something pretty similar to this but gdb couldn't find files whose paths started with `external/...`. I ended up starting in `bazel-` (In this case, it'd be `bazel-Cpp`). It seemed that all source paths were correct when starting in that dir. – Mark Jan 16 '19 at 18:27
  • That comment is real answer to the question! – Dmitry Apr 03 '19 at 18:06
  • hi Picaud Vincent, you have any configs for setting up debugging a Bazel project on CLion IDE (version 2020.1.3, ubuntu) with the Bazel plugin? ...Thanks in advance! – drstoop Jan 30 '21 at 20:04
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    @drstoop no sorry, I cannot help there: I have never used CLion IDE nor have access to it. – Picaud Vincent Jan 30 '21 at 20:10
  • @PicaudVincent you are the wind beneath my wings. Many thanks! – netskink Jun 10 '22 at 20:02