GDB Scripts

Audience

This section is written for those with entry level understanding of GDB.

Introduction

This repo contains gdb scripts to peruse memory of restraintd. It is especially useful to derive data from memory as a result of a crash.

Steps if restraintd crashed

If restraintd crashes, you gather the core file and prepare an environment similar to that which restraint crashed. So if the crash occured in RHEL7, then you install a machine with RHEL7 and same version of restraintd. You also need the following installed:

   ```
   yum install gdb
   ```

Then do

```
gdb restraintd the-core-file-found-from-crash
```

When you execute this the first time it will fail as you are missing the symbols. It will report to you what you need to run to install the symbols. The command given I found to change depending on your OS version. I only worked with RHEL 7&8 and saw different results on both. It would be something similar to the folllowing in RHEL OS.

  ```
  yum debuginfo-install restraint-0.1.39-1.el8bkr.x86_64
  ```

The above command installs the restraint symbols as well as symbols for its dependency libraries.

Restart gdb once the debuginfo is installed.

Setup and Use of gdb scripts

Clone this repo containing the gdb scripts. Scripts can be found in directory scripts. Sample output can be found in sample_out. In gdb, do the following to pull the scripts into your environment.

  ```
  source ${your-root-dir}/gdb/scripts/gdb_set_env
  source ${your-root-dir}/gdb/scripts/gdb_peruse_recipe_task
  source ${your-root-dir}/gdb/scripts/gdb_peruse_glib
  ```

The first script should always be sourced since the other scripts may depend on it. The environment scripts contains functions which allow you to enable debugging to external file.

You'll likely have to move up/down the stack to get to the restraint function where the data structures needed are visible to the 'C' function. So you run gdb bt to see the backtrace, then run up 10 for example to move to the function with visibility.

From there, you can run the scripts like the following.

  ```
  print_all_app_data app_data
  ```

Each function has a description of use so you should refer to the individual files for details.