GRASS Debugging

The following hints assume to work on a working-copy of the GRASS CVS dierctory.

Additionally it is good to have set the debbugging symbols during compile-time. Do not strip the libraries or use optimization in the compile. see INSTALL and doc/debugging.txt in the source code for more information.

Setting Environment-variables (numbers: 1-5)

• g.gisenv set="DEBUG=1"
• A higher debug level means you see more messages.
• These messages are always present regardless of compiler settings.

Using GDB

• running a programm inside GDB works (installation of GDB required :-), (on debian: apt-get install gdb)
• gdb `which v.in.ogr`
• run "out=bla dsn="PG:dbname=postgis user=me" olayer=postgislayer"
• when it crashes, just type bt full for a backtrace
• type "l" to list where in the source code it got to
• type frame 2 to switch to the second level function (see the backtrace), there you can again type "l" to see where it got up to.

Using strace

• running the command through strace could give you another hint what is going wrong somewhere.
• for example: strace v.in.ogr out=bla dsn="PG:dbname=postgis user=me" olayer=postgislayer

Skimming ChangLog for changes

• use the tool cvs2cl.pl for generating a local changelog-file

Using DDD (gdb graphical frontend)

• running a programm inside ddd works (installation of ddd and gdb required :-), (on debian: apt-get install gdb ddd)
• ddd `which v.in.ogr`

http://mpa.itc.it/markus/grass61/debugging/crash_1_small.jpg

• Run (from main menu PROGRAM): "out=bla dsn="PG:dbname=postgis user=me" olayer=postgislayer"

http://mpa.itc.it/markus/grass61/debugging/ddd_1_small.jpg

• run with parameters
• when it crashes, use the UP menu item to trace back

http://mpa.itc.it/markus/grass61/debugging/ddd_2_going_up_small.jpg

• reach the line where it crashed
• set a breakpoint, then run again to stop before the crash

http://mpa.itc.it/markus/grass61/debugging/ddd_3_breakpoint_small.jpg

• right mouse button on variables permits to display them etc.

http://mpa.itc.it/markus/grass61/debugging/ddd_4_displ_vars_small.jpg

• figure out why it crashed there. This requires PATIENCE. But you will nearly save the world if you identify the problem :-)

Using kdbg (gdb graphical frontend)

• kdbg is not unlike DDD, but it's a KDE application.
• Use is similar to ddd.
• Start with (within GRASS):
  

kdbg `which g.module`

• Fill in command line arguments with menu item Execution->Arguments.
• Open the View->Locals window.
• Click the Run icon (or Execution->Run) and see where it breaks.
• Set pause-points by clicking a red stop-sign to the left of the "+" on a line of the source code. From there you can step through instructions.
• Explore the values of variables in the locals window.