Pgdbg

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This is not a complete article: This is a draft, a work in progress that is intended to be published into an article, which may or may not be ready for inclusion in the main wiki. It should not necessarily be considered factual or authoritative.

PGDBG is a powerful and simple tool for debugging both MPI-parallel and OpenMP thread-parallel Linux applications. It is included in the PGI compiler package and configured for OpenMP thread-parallel debugging.

For the most of the C, C++, or Fortran 77 codes one can use a regular GNU debugger such as GDB. However, the Fortran 90/95 programs are not handled very well by the GDB. The Portland Group has developed a debugger called pgdbg which is more suited for such codes. Pgdbg is provided in two modes: a graphical mode with the enabled X11 forwarding or a text mode.

Quickstart guide

Using PGDBG usually consists of two steps:

1. Compilation: Compile the code with the debugging enabled
2. Execution and analysis: Execute the code and analyze the results

Both steps can be accomplished in either command-line mode or graphical mode.

Environment modules

Before you start profiling with PGDBG, the appropriate module needs to be loaded. PGDBG is part of the PGI compiler package, so run module avail pgi to see what versions are currently available with the compiler, MPI, and CUDA modules you have loaded. For a comprehensive list of PGI modules, run module -r spider '.*pgi.*'.
As of December 2018, these were:

• pgi/13.10
• pgi/17.3

Use module load pgi/version to select a version; for example, to load the PGI compiler version 17.3, use

[name@server ~]$ module load pgi/17.3

Compiling your code

To be able to debug with pgdbg you first need to compile your code with debugging information enabled. With the pgdbg you do so by adding a debugging flag "-g":

[name@server ~]$ pgcc -g program.c -o program

Command-line mode

Analysis: Once your code is compiled with the proper options, you can run the PGDBG for the analysis. The debugger's default user interface is a graphical user interface or GUI. However, if for some reasons you don't want to run in GUI or don't have X11 forwarding, you can run pgdbg in a text mode by adding an extra option "-text" :

[name@server ~]$ pgdbg -text program arg1 arg2

Graphical mode

The debugger's default user interface is a graphical user interface or GUI. If you have set the X11 forwarding then the pgdbg will start in the graphical mode in a pop-up window. If you don't have X11 forwarding, you can run pgdbg in a text mode by adding an extra option "-text" :

[name@server ~]$ pgdbg -text program arg1 arg2

PGDGB in graphical mode(click for a larger image)

As the illustration shows, the GUI is divided into several areas:

• the menu bar
  • The source window, illustrated in Figure 2, displays the source code for the current location
• main
• toolbar
• source window
• program I/O window
• and debug information tabs.

Message Passing Interface