Displaying and Modifying Storage

You can display the contents of storage using the dump and dis commands. The dump command displays an area of storage in dump format whereas the dis command attempts to disassemble the storage area into 390 instructions.

You can modify storage using the set char, set half, set word and set dword commands. The set dword command alters doublewords (8 bytes) of storage. The set word command alters fullwords (4 bytes) of storage. The set half command alters halfwords (2 bytes) of storage. The set char command alters bytes of storage. All of these commands can be used to alter multiple storage locations.

Displaying and Modifying Registers and the PSW

You can use the show regs, show aregs, show fregs and show cregs commands to display the contents of the general, access, floating point and control registers and you can use the show command to display the contents of an individual floating point register in the desired format. You can also use the set command to modify any of these registers. You can display and alter the Program Status Word (PSW) through the show psw and set psw commands. The general registers, the PSW and the next instruction to be executed can also be displayed just before each instruction is to be executed when tracing is on.

Setting Break Points, Watch Points and Event Traps

Break points are locations which can be set to halt the run command when an instruction is fetched from that location. You can set break points using the set break command and you can list or delete them using the show break and drop break commands. If you want to know how the program branches to a certain instruction, set a break point at the instruction, issue the run command and then issue the show itrace command to see the instructions recently executed.

Watch points are locations which can be set to halt the run command when an instruction alters storage at the location. You can set watch points using the set watch command and you can list or delete them using the show watch and drop watch commands. If you want to know why an area of storage is being modified, set a watch point over the area.

Event traps can be set to halt the run command or execute one or more commands when an event occurs. You can set event traps using the set event command and you can list or delete them using the show event and drop event commands. Event traps are useful for setting break points in a module once it is loaded into storage.

Tracing, Stepping and Running

You can use the step command to execute the instruction pointed to by the PSW. You can also use the run command to start running the program from the instruction pointed to be the PSW until the next break or watch point or until the program ends. You can use the set trace command to obtain an execution trace of the general registers, PSW and instructions as your program runs.

With the show itrace command you can display the history of recently executed instructions. You can also disable and enable the instruction history or alter the size of the history buffer using the set itrace command. In addition, you can use the set stgtrace command to have the debugger print a message each time storage is allocated or freed from a user subpool.

Finally, you use the quit command to exit the debugger. If this is done before the program ends, the Tachyon Operating System interprets this action as an operator cancellation of the job.

Using Command and Log Files

You can create files containing lists of commands and you can execute the commands in these files using the call command. The call command may also be used within command files. You can add comments to command files using the rem command and you can display messages using the show command. Parameters on the call statement can be used in the statements in the command files.

You can also create a file containing a log of your debugging session set log command. The log will contain the commands that you entered or that were read from command files as well as the output of the commands. The log file name defaults to tie.log unless overridden by the set log file command.

Using Command Aliases and Function Keys

You can create you own debugger commands by assigning an alias name to a list of one or more commands using the set alias command. Once an alias is defined, you can use it just as if it was a built-in command. When an alias command is used, parameters following the alias name can be substituted into the alias command list. Help strings and files can be associated with command aliases when they are defined. You can display and delete command aliases using the show alias and drop alias commands.

On Windows, you can assign a list of one or more commands to a keyboard function key using the set key command. Once defined, if the function key is the first key pressed after the debugger prompt is displayed, the assigned list of commands will be entered as if they were typed instead of the function key. You can display and delete function key definitions using the show key and drop key commands.

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© Copyright 1998-2005, Tachyon Software® LLC.
Last modified on November 30, 2005