EBC Exercise 14 gdb Debugging

As the code becomes more complex, more powerful debugging tools are needed. The GNU Project debugger (gdb) is the granddaddy of all debuggers. In this exercise you will learn how to install and use it on the Beagle. In a later exercise you will learn how to install it on your host and debug the Beagle remotely.

gdb
gdb, the GNU Project debugger, allows you to see what is going on inside another program while it executes -- or what another program was doing at the moment it crashed.

gdb can do four main kinds of things to help you catch bugs in the act:


 * Start your program, specifying anything that might affect its behavior.
 * Make your program stop on specified conditions.
 * Examine what has happened, when your program has stopped.
 * Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.

The program being debugged can be written in Ada, C, C++, Objective-C, Pascal (and many other languages). Those programs might be executing on the same machine as GDB (native) or on another machine (remote). GDB can run on most popular UNIX and Microsoft Windows variants.

For our lab we'll be using a C program and do local execution on the Beagle.

Installing gdb
On your Beagle run:

beagle$ opkg update beagle$ opkg install gdb

A gdb Tutorial
There are a number of gdb tutorials out there. I like Using GNU's GDB Debugger By Peter Jay Salzman.

beagle$ bunzip2 file.tar.bz2 beagle$ tar xvf file.tar
 * Read Chapter 1, the Intro
 * Do the examples in Chapters 2 (skip the spinning cube example in 2.8 unless you are interested in openGL) Hint: the commands to uncompress a .tar.bz2 file are:
 * Do Chapter 3 examples
 * Look over Breakpoints in Chapter 4

(RMS's gdb Debugger Tutorial may be another good reference.)

Chapter 3 has you download a Makefile that will fail because it can't find ctags. Either comment out that line, or follow the directions below to install ctags.

Remote debugging with gdb
You can run a gdb server on the bone and control it from a gdb session on your host. EBC Exercise 28 Remote gdb and more has details on how this is done.

ctags on the host
Here's what I did to get ctags running in gedit on the host.

host$ sudo apt-get install exuberant-ctags

gedit has a ctags plugin. Details are here. Download from here. Installation details are here.

You also need to load libgnomeprintui. Go to System:Administration:Synaptic Package Manager and search for libgnomeprintui and select it. Click Apply.

NOTE FOR Newest Ubuntu Releases! Synaptic Package Manager is not natively installed, do the following commands:

host$ sudo apt-get install synaptic

Then you can install the above file.

Now you can use ctags. Go a directory with some .c and .h files and run:

host$ ctags *.c *.h host$ gedit *.c *.h

This will create a file called tags that tells where each symbol is defined. Enable the ctags plugin by going to Edit:Preferences. Click the Plugins tag and scroll down to Symbol Browser and check it. You can click the Configure Plugin button to apply some options.

To make the symbols visible, select  View:Side Pane in gedit. Click the symbol at the bottom of the side pane. You will now see all the symbols. Click on one to go to its definition.