Swat Introduction

GEOS SDK TechDocs

1 DOS Command Line Options

Most programmers are familiar with the process of debugging code. Many, however, will not be familiar with the issues of debugging programs in an entirely object-oriented, multithreaded system in which memory is often sharable by multiple programs. Because this type of system presents not only incredible power but also a new class of potential bugs, the GEOS tool kit provides a new class of symbolic debugger.

Swat is more than just a debugging program; it is an extensible debugging environment which you can tailor to your needs. Because all Swat commands are programmed in a special language called Tool Command Language (Tcl), you can write your own commands or extend existing commands. Tcl was originally developed by Professor John Ousterhout at the University of California in Berkeley, California. Swat itself was developed during a project headed by professor Ousterhout for a distributed multiprocessing operating system; Geoworks gained permission from the university to use and modify Swat. Since then, we have tailored it for use with GEOS; thus, it is the most appropriate debugger for any GEOS programmer.

Swat is essentially a system debugger, as opposed to an application debugger. This is an important distinction, due to the multithreaded nature of individual GEOS applications--each application may have more than one thread, and a system debugger greatly eases the debugging process for such applications. Swat also has many other features that make it preferable to other debuggers:

• Ideal for multithreaded environment
  Because Swat was initially designed for debugging multithreaded system software, it is ideal for use on multithreaded applications in the GEOS environment.
• Extremely flexible
  Nearly every part of Swat you will use is written in Tcl. Swat allows you to create your own commands or extend existing commands by using the Tcl language; you can examine, print, and modify just about any data structure using various Tcl commands. For large applications and projects, the customization this offers can be a tremendous asset.
• Extensive access to data structures
  You can examine any byte in the test PC's memory while Swat is attached. You can examine any basic or complex data structure. For example, the "pobject" command ("print object") prints the entire instance data of the specified object. You can specify memory locations with symbols, registers, addresses, pointers, or a number of other ways.
• Easy modification of code and data
  Using Tcl commands, you can change the contents of a register or memory location. You can also create patches to be executed at certain points in your program; this speeds up debugging by reducing the fix-compile-download-attach-debug cycle to a simple fix-debug cycle.
• Interactive single-step facility
  By using Swat's single-step command, you can execute a single instruction at a time. Swat shows you all the inputs going in to the instruction so you can more easily keep track of what's going on.
• Facilities for watching messages and objects
  Swat has several "watch" facilities. For example, you can let GEOS continue executing while watching a particular object; Swat will display all messages sent to the object, along with the data passed. You can also watch a particular message; Swat will display the destination and passed data each time the message is sent.
• On-line help system
  Swat commands are documented on-line. The help facility is available from the basic Swat command prompt, and you can use it either as an interactive help shell or to get help on one particular topic.

Swat also offers many other features that both novices and experts will use. As you gain familiarity with Swat while using Swat with the sample applications and with your own programs, you will discover your own preferred methods of debugging.

  1 DOS Command Line Options
  2 Notation
  3 Address Expressions
  4 On-line Help
  5 Essential Commands
    5.1 Cycle of Development
    5.2 Attaching and Detaching
    5.3 Breakpoints and Code Stepping
    5.4 Examining and Modifying Memory
    5.5 Other Important Commands
  6 Additional Features

GEOS SDK TechDocs

1 DOS Command Line Options