4 Debugging

This chapter describes different HP Fortran features for debugging programs. These features include compile-line options, compiler directives, and programming tools that are useful for locating errors in your program. More specifically, this chapter discusses the following topics:

•Using the HP WDB debugger

•Stripping debugging information

•Handling runtime exceptions

•Using debugging lines

Using the HP WDB debugger

The HP WDB debuggeris the primary tool for debugging HP Fortran programs. The debugger provides such basic debugging functions as program control, process control, program and data monitoring, and expression evaluation. The debugger has both a graphical interface and a line-mode interface.

The debugger software includes different managers that enable it to handle different source languages, target machines, object file formats, and user formats. The Fortran language manager allows you to use Fortran syntax when entering expressions on the debugger command line.

Before beginning a debugging session, you must compile the program with the -gcompile-line option. If you compile and link separately, you must use the -goption on both command lines. The option causes the compiler to generate additional information needed by the debugger and to insert it into the output code.

After compiling your program with the -goption, invoke the debugger with the wdbcommand, supplying the name of the executable as an argument. For example, the following command compiles prog.f90for debugging:

$ f90 -g prog.f90 -o db_prog

Here is the command to start debugging the executable program:

$ wdb db_prog

You can use the debugger to debug code that has been optimized at levels 0, 1, and 2. To debug optimized code, compile the program with both the -gand +Oopt-leveloptions, where opt-level is 0, 1, or 2. The following command line prog.f90at optimization level 2 and prepares for debugging:

$ f90 +O2 -g prog.f90 -o db_prog

Compiling with the -goption increases the size of both the object file and the executable file. After you have debugged your program and are ready to build the production version, you may want to recompile without the -goption.

For complete information about HP WDB debugger, see http://www.hp.com/go/wdb. Printed and online documentation are available at this site.

Stripping debugging information

Programs compiled with HP Fortran include minimal debugging information in the executable program. This information consists of a symbol table—a list of all the symbols in your program and their offset addresses. The symbol table provides the information needed to produce a procedure traceback. It is also used by the debugger and by the CXperf performance analysis tool.

However, the symbol table is not the same as the debugging information that is added to your program when you compile with the -goption. The symbol table is added to an executable even if the program is not compiled with the -goption.

76 Debugging