Document revision date: 30 March 2001

## OpenVMS Debugger Manual

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This command causes the debugger to execute the program to the next instruction when a STEP command is entered, and not to display lines of source code with each STEP command.

#2
    DBG> SET STEP LINE,INTO,NOSYSTEM,NOSHARE

> This command causes the debugger to execute the program to the next line when a STEP command is entered, and to step into called routines in user space only. The debugger steps over routines in system space and in shareable images.

## SET TASK|THREAD

> Changes characteristics of one or more tasks of a tasking program (also called a multithread program).

### Format

> SET TASK [task-spec[,...]]

### Parameters

> #### task-spec

> Specifies a task value. Use any of the following forms:
> - When the event facility is THREADS:
>   - A task (thread) ID number as declared in the program, or a language expression that yields a task ID number.
>   - A task ID number (for example, 2), as indicated in a SHOW TASK display.
> - When the event facility is ADA:
>   - A task (thread) name as declared in the program, or a language expression that yields a task value. You can use a path name.
>   - A task ID (for example, %TASK 2), as indicated in a SHOW TASK display.
> - One of the following task built-in symbols:

>   %ACTIVE_TASK | The task that runs when a GO, STEP, CALL, or EXIT command executes.
>   %CALLER_TASK | (Applies only to Ada programs.) When an accept statement executes, the task that called the entry associated with the accept statement.
>   %NEXT_TASK | The task after the visible task in the debugger's task list. The ordering of tasks is arbitrary but consistent within a single run of a program.
>   %PREVIOUS_TASK | The task previous to the visible task in the debugger's task list.
>   %VISIBLE_TASK | The task whose call stack and register set are the current context for looking up symbols, register values, routine calls, breakpoints, and so on.

> Do not use the asterisk (*) wildcard character. Instead, use the /ALL qualifier. Do not specify a task with /ALL or /TIME_SLICE. If you do not specify a task or /ALL with /ABORT, /[NO]HOLD, /PRIORITY, or /RESTORE, the visible task is selected.

### Qualifiers

> #### /ABORT

> Marks the specified tasks for termination. Termination occurs at the next allowable point after a specified task resumes execution.

> For Compaq Ada tasks, the effect is identical to executing an Ada abort statement for the tasks specified and causes these tasks to be marked as abnormal. Any dependent tasks are also marked for termination.

> For POSIX Threads threads, use the following command:

>     PTHREAD tset -c thread-number

> #### /ACTIVE

> Makes the specified task the active task, which is the task that runs when a STEP, GO, CALL, or EXIT command executes. This causes a task switch to the new active task and makes that task the visible task. The specified task must be in either the RUNNING or READY state. When using /ACTIVE, you must specify one task.

> The SET TASK/ACTIVE command is supported for Compaq Ada on VAX only. For POSIX Threads programs or Compaq Ada on Alpha programs, use one of the following alternatives:

> - For query-type actions, use the SET TASK/VISIBLE command.
> - To gain control of execution, use a strategic placement of breakpoints.
> - Use the PTHREAD tset -a thread-number command.

> #### /ALL

> Applies the SET TASK command to all tasks.

> #### /HOLD

> #### /NOHOLD (default)

> When the event facility is THREADS, use the PTHREAD tset -h thread-number or the PTHREAD tset -n thread-number command.

> Controls whether a specified task is put on hold. The /HOLD qualifier puts a specified task on hold.

> Putting a task on hold prevents a task from entering the RUNNING state. A task put on hold is allowed to make other state transitions; in particular, it can change from the SUSPENDED to the READY state.

> A task already in the RUNNING state (the active task) can continue to execute as long as it remains in the RUNNING state, even though it is put on hold. If the task leaves the RUNNING state for any reason (including expiration of a time slice, if time slicing is enabled), it will not return to the RUNNING state until released from the hold condition.

> You can override the hold condition and force a task into the RUNNING state with the SET TASK/ACTIVE command even if the task is on hold.

> The /NOHOLD qualifier releases a specified task from hold.

> #### /PRIORITY=n

> When the event facility is THREADS, use the PTHREAD tset -s thread-number command.

> Sets the priority of a specified task to n, where n is a decimal integer from 0 to 15. This does not prevent the priority from later changing in the course of execution, for example, while executing an Ada rendezvous or POSIX Threads synchronization event. This qualifier does not affect a task's scheduling policy.

> #### /RESTORE

> (Compaq Ada on VAX only) Restores the priority of a specified task to the priority it had when it was created. Does not affect the scheduling priority of the task.

> #### /TIME_SLICE=t

> Supported for Compaq Ada on VAX only. Sets the time-slice duration to the value t, where t is a decimal integer or real value representing seconds. The set value overrides the time-slice value specified in the program, if any. To disable time slicing, use /TIME_SLICE=0.0. /TIME_SLICE is valid only when the event facility is ADA.

> #### /VISIBLE

> Makes the specified task the visible task, which is the task whose call stack and register set are the current context for looking up symbols, register values, routine calls, breakpoints, and so on. Commands such as EXAMINE are directed at the visible task. The /VISIBLE qualifier does not affect the active task. When using /VISIBLE, you must specify one task.

### Description

> Note SET TASK and SET THREAD are synonymous commands. They perform identically.

> The SET TASK command enables you to establish the visible task and the active task, control the execution of tasks, and cause task state transitions, directly or indirectly.

> To determine the current state of a task, use the SHOW TASK command. The possible states are RUNNING, READY, SUSPENDED, and TERMINATED.

> Related commands:

> > DEPOSIT/TASK
> > EXAMINE/TASK
> > SET BREAK/EVENT
> > SET TRACE/EVENT
> > (SET, SHOW) EVENT_FACILITY
> > SHOW TASK|THREAD

### Examples

#1
    DBG> SET TASK/ACTIVE %TASK 3

> (Event facility = ADA) This command makes task 3 (task ID = 3) the active task.

#2
    DBG> PTHREAD tset -a 3

> (Event facility = THREADS) This command makes task 3 (task ID = 3) the active task.

#3
    DBG> SET TASK %NEXT_TASK

> This command makes the next task in the debugger's task list the visible task. (The /VISIBLE qualifier is a default for the SET TASK command.)

#4
    DBG> SET TASK/HOLD/ALL
    DBG> SET TASK/ACTIVE %TASK 1
    DBG> GO
        ...
    DBG> SET TASK/ACTIVE %TASK 3
    DBG> STEP
        ...

> In this example, the SET TASK/HOLD/ALL command freezes the state of all tasks except the active task. Then, SET TASK/ACTIVE is used selectively (along with the GO and STEP commands) to observe the behavior of one or more specified tasks in isolation.

## SET TERMINAL

> Sets the terminal-screen height or width that the debugger uses when it formats screen and other output.

> Note This command is not available in the Compaq DECwindows Motif for OpenVMS user interface to the debugger.

### Format

> SET TERMINAL

### Qualifiers

> #### /PAGE:n

> Specifies that the terminal screen height should be set to n lines. You can use any value from 18 to 100.

> #### /WIDTH:n

> Specifies that the terminal screen width should be set to n columns. You can use any value from 20 to 255. For a VT100-, VT200-, or VT300 series terminal, n is typically either 80 or 132.

> #### /WRAP

> Tells the debugger to wrap output text in predefined display OUT at the column specified by the /WIDTH qualifier. If you do not specify /WIDTH in the current command, /WRAP defaults to the %WIDTH setting.

### Description

> The SET TERMINAL command enables you to define the portion of the screen that the debugger has available for formatting screen output.

> This command is useful with VT100-, VT200-, or VT300-series terminals, where you can set the screen width to typically 80 or 132 columns. It is also useful with workstations, where you can modify the size of the terminal-emulator window that the debugger uses.

> You must specify at least one qualifier. You can specify all. The /PAGE and /WIDTH qualifiers each require a value.

> When you enter the SET TERMINAL command, all display window definitions are automatically adjusted to reflect the new screen dimensions. For example, RH1 changes dimensions proportionally to remain in the top right half of the screen.

> Similarly, all "dynamic" display windows are automatically adjusted to maintain their relative proportions. Note that all display windows are dynamic unless referenced with the DISPLAY/NODYNAMIC command. In that case, the display window retains its current dimensions after subsequent SET TERMINAL commands. However, you can use the DISPLAY command to reconfigure the display window (you can also use keypad-key combinations, such as BLUE-MINUS, to enter predefined DISPLAY commands).

> Related commands:

> > DISPLAY/[NO]DYNAMIC
> > EXPAND
> > (SET,SHOW,CANCEL) WINDOW
> > SHOW TERMINAL

### Example

    DBG> SET TERMINAL/WIDTH:132

> This command specifies that the terminal screen width be set to 132 columns.

## SET TRACE

> Establishes a tracepoint at the location denoted by an address expression, at instructions of a particular class, or at the occurrence of specified events.

### Format

> SET TRACE [address-expression[,...]]
> [WHEN(conditional-expression)]
> [DO(command[;...])]

### Parameters

> #### address-expression

> Specifies an address expression (a program location) at which a tracepoint is to be set. With high-level languages, this is typically a line number, a routine name, or a label, and can include a path name to specify the entity uniquely. More generally, an address expression can also be a memory address or a register and can be composed of numbers (offsets) and symbols, as well as one or more operators, operands, or delimiters. For information about the operators that you can use in address expressions, type Help Address_Expressions.

> Do not specify the asterisk (*) wildcard character. Do not specify an address expression with the following qualifiers:

> > /ACTIVATING
> > /BRANCH
> > /CALL
> > /EXCEPTION
> > /INSTRUCTION
> > /INSTRUCTION=(opcode[,...]) (VAX only)
> > /INTO
> > /[NO]JSB (VAX only)
> > /LINE
> > /OVER
> > /[NO]SHARE
> > /[NO]SYSTEM
> > /TERMINATING
> > /VECTOR_INSTRUCTION (VAX only)

> The /MODIFY and /RETURN qualifiers are used with specific kinds of address expressions.

> If you specify a memory address or an address expression whose value is not a symbolic location, check (with the EXAMINE command) that an instruction actually begins at the byte of memory so indicated. If an instruction does not begin at this byte, a run-time error can occur when an instruction including that byte is executed. When you set a tracepoint by specifying an address expression whose value is not a symbolic location, the debugger does not verify that the location specified marks the beginning of an instruction.

> On VAX processors, CALLS and CALLG routines start with an entry mask.

> #### conditional-expression

> Specifies a conditional expression in the currently set language that is to be evaluated whenever execution reaches the tracepoint. (The debugger checks the syntax of the expressions in the WHEN clause when execution reaches the tracepoint, not when the tracepoint is set.) If the expression is true, the debugger reports that a tracepoint has been triggered. If an action (DO clause) is associated with the tracepoint, it will occur at this time. If the expression is false, a report is not issued, the commands specified by the DO clause (if one was specified) are not executed, and program execution is continued.

> #### command

> Specifies a debugger command to be executed as part of the DO clause when trace action is taken. The debugger checks the syntax of the commands in a DO clause when it executes the DO clause, not when the tracepoint is set.

### Qualifiers

> #### /ACTIVATING

> Causes the debugger to trace when a new process comes under debugger control. See also the /TERMINATING qualifier.

> #### /AFTER:n

> Specifies that trace action not be taken until the nth time the designated tracepoint is encountered (n is a decimal integer). Thereafter, the tracepoint occurs every time it is encountered provided that conditions in the WHEN clause (if specified) are true. The SET TRACE/AFTER:1 command has the same effect as SET TRACE.

> #### /BRANCH

> Causes the debugger to trace every branch instruction encountered during program execution. See also the /INTO and /OVER qualifiers.

> #### /CALL

> Causes the debugger to trace every call instruction encountered during program execution, including the return instruction. See also the /INTO and /OVER qualifiers.

> #### /EVENT=event-name

> Causes the debugger to trace the specified event (if that event is defined and detected by the current event facility). If you specify an address expression with /EVENT, causes the debugger to trace whenever the specified event occurs for that address expression. You cannot specify an address expression with certain event names.

> Event facilities are available for programs that call Ada or SCAN routines or that use POSIX Threads services. To identify the current event facility and the associated event names, use the SHOW EVENT_FACILITY command.

> #### /EXCEPTION

> Causes the debugger to trace every exception that is signaled. The trace action occurs before any application-declared exception handlers are invoked.

> As a result of a SET TRACE/EXCEPTION command, whenever your program generates an exception, the debugger reports the exception and resignals the exception, thus allowing any application-declared exception handler to execute.

> #### /INSTRUCTION

> #### /INSTRUCTION[=(opcode[,...])] (VAX only)

> When you do not specify an opcode, causes the debugger to trace every instruction encountered during program execution.

> (VAX only) If you specify one or more opcodes, causes the debugger to trace every instruction whose opcode is in the list.

> If you specify a vector instruction, do not include an instruction qualifier (/UNALIGNED_DATA, /VECTOR_INSTRUCTION, /MODIFY, /0, or /1) with the instruction mnemonic.

> See also the /INTO and /OVER qualifiers.

> #### /INTO

> (Default) Applies only to tracepoints set with the following qualifiers (that is, when an address expression is not explicitly specified):

> > /BRANCH
> > /CALL
> > /INSTRUCTION
> > /INSTRUCTION=(opcode[,...]) (VAX only)
> > /LINE
> > /VECTOR_INSTRUCTION (VAX only)

> When used with those qualifiers, /INTO causes the debugger to trace the specified points within called routines (as well as within the routine in which execution is currently suspended). The /INTO qualifier is the default and is the opposite of /OVER.

> When using /INTO, you can further qualify the trace action with the /[NO]JSB, /[NO]SHARE, and /[NO]SYSTEM qualifiers.

> #### /JSB

> #### /NOJSB

> (VAX only) Qualifies /INTO. Use with /INTO and one of the following qualifiers:

> > /BRANCH
> > /CALL
> > /INSTRUCTION
> > /INSTRUCTION=(opcode[,...])
> > /LINE
> > /VECTOR_INSTRUCTION

> The /JSB qualifier is the default for all languages except DIBOL. It lets the debugger set tracepoints within routines that are called by the JSB or CALL instruction. The /NOJSB qualifier (the DIBOL default) specifies that tracepoints not be set within routines called by JSB instructions. In DIBOL, application-declared routines are called by the CALL instruction and DIBOL Run-Time Library routines are called by the JSB instruction.

> #### /LINE

> Causes the debugger to trace the beginning of each source line encountered during program execution. See also the /INTO and /OVER qualifiers.

> #### /MODIFY

> Causes the debugger to trace when an instruction writes to and changes the value of a location indicated by a specified address expression. The address expression is typically a variable name.

> The SET TRACE/MODIFY X command is equivalent to SET WATCH X DO(GO). The SET TRACE/MODIFY command operates under the same restrictions as SET WATCH.

> If you specify an absolute address for the address expression, the debugger might not be able to associate the address with a particular data object. In this case, the debugger uses a default length of 4 bytes. You can change this length, however, by setting the type to either WORD (SET TYPE WORD, which changes the default length to 2 bytes) or BYTE (SET TYPE BYTE, which changes the default length to 1 byte). The SET TYPE LONGWORD command restores the default length of 4 bytes.

> #### /OVER

> Applies only to tracepoints set with the following qualifiers (that is, when an address expression is not explicitly specified):

> > /BRANCH
> > /CALL
> > /INSTRUCTION
> > /INSTRUCTION=(opcode[,...]) (VAX only)
> > /LINE
> > /VECTOR_INSTRUCTION (VAX only)

> When used with those qualifiers, /OVER causes the debugger to trace the specified points only within the routine in which execution is currently suspended (not within called routines). The /OVER qualifier is the opposite of /INTO (which is the default).

> #### /RETURN

> Causes the debugger to break on the return instruction of the routine associated with the specified address expression (which can be a routine name, line number, and so on). Breaking on the return instruction enables you to inspect the local environment (for example, obtain the values of local variables) while the routine is still active. Note that the view of a local environment may differ depending on your architecture. On VAX processors, this qualifier can only be applied to routines called with a CALLS or CALLG instruction; it cannot be used with JSB routines. On Alpha processors, this qualifier can be applied to any routine.

> The address-expression parameter is an instruction address within a routine. It can simply be a routine name, in which case it specifies the routine start address. However, you can also specify another location in a routine, so you can see only those returns that are taken after a certain code path is followed.

> A SET TRACE/RETURN command cancels a previous SET TRACE if you specify the same address expression.

> #### /SHARE (default)

> #### /NOSHARE

> Qualifies /INTO. Use with /INTO and one of the following qualifiers:

> > /BRANCH
> > /CALL
> > /INSTRUCTION
> > /INSTRUCTION=(opcode[,...]) (VAX only)
> > /LINE
> > /VECTOR_INSTRUCTION (VAX only)

> The /SHARE qualifier permits the debugger to set tracepoints within shareable image routines as well as other routines. The /NOSHARE qualifier specifies that tracepoints not be set within shareable images.

> #### /SILENT

> #### /NOSILENT (default)

> Controls whether the "trace..." message and the source line for the current location are displayed at the tracepoint. The /NOSILENT qualifier specifies that the message is displayed. The /SILENT qualifier specifies that the message and source line are not displayed. The /SILENT qualifier overrides /SOURCE.

> #### /SOURCE

> #### /NOSOURCE (default)

> Controls whether the source line for the current location is displayed at the tracepoint. The /SOURCE qualifier specifies that the source line is displayed. The /NOSOURCE qualifier specifies that the source line is not displayed. The /SILENT qualifier overrides /SOURCE. See also the SET STEP [NO]SOURCE command.

> #### /SYSTEM (default)

> #### /NOSYSTEM

> Qualifies /INTO. Use with /INTO and one of the following qualifiers:

> > /BRANCH
> > /CALL
> > /INSTRUCTION
> > /INSTRUCTION=(opcode[,...]) (VAX only)
> > /LINE
> > /VECTOR_INSTRUCTION (VAX only)

> The /SYSTEM qualifier permits the debugger to set tracepoints within system routines (P1 space) as well as other routines. The /NOSYSTEM qualifier specifies that tracepoints not be set within system routines.

> #### /TEMPORARY

> Causes the tracepoint to disappear after it is triggered (the tracepoint does not remain permanently set).

> #### /TERMINATING

> (Default) Causes the debugger to trace when a process does an image exit. The debugger gains control and displays its prompt when the last image of a one-process or multiprocess program exits. See also the /ACTIVATING qualifier.

> #### /VECTOR_INSTRUCTION

> (VAX only) Causes the debugger to trace every vector instruction encountered during execution. See also the /INTO and /OVER qualifiers.

### Description

> When a tracepoint is triggered, the debugger takes the following actions:
> 1. Suspends program execution at the tracepoint location.
> 2. If you specified /AFTER when you set the tracepoint, checks the AFTER count. If the specified number of counts has not been reached, execution is resumed and the debugger does not perform the remaining steps.
> 3. Evaluates the expression in a WHEN clause, if you specified one when you set the tracepoint. If the value of the expression is false, execution is resumed and the debugger does not perform the remaining steps.
> 4. Reports that execution has reached the tracepoint location by issuing a "trace..." message, unless you specified /SILENT.
> 5. Displays the line of source code corresponding to the tracepoint, unless you specified /NOSOURCE or /SILENT when you set the tracepoint or entered a previous SET STEP NOSOURCE command.
> 6. Executes the commands in a DO clause, if you specified one when you set the tracepoint.
> 7. Resumes execution.

> You set a tracepoint at a particular location in your program by specifying an address expression with the SET TRACE command. You set a tracepoint on consecutive source lines, classes of instructions, or events by specifying a qualifier with the SET TRACE command. Generally, you must specify either an address expression or a qualifier, but not both. Exceptions are /EVENT and /RETURN.

> The /LINE qualifier sets a tracepoint on each line of source code.

> The following qualifiers set tracepoints on classes of instructions. Using these qualifiers and /LINE causes the debugger to trace every instruction of your program as it executes and thus significantly slows down execution.

> > /BRANCH
> > /CALL
> > /INSTRUCTION
> > /INSTRUCTION=(opcode[,...]) (VAX only)
> > /RETURN
> > /SYSEMULATE (Alpha only)
> > /VECTOR_INSTRUCTION (VAX only)

> The following qualifiers set tracepoints on classes of events:

> > /ACTIVATING
> > /EVENT=event-name
> > /EXCEPTION
> > /TERMINATING

> The following qualifiers affect what happens at a routine call:

> > /INTO
> > /[NO]JSB (VAX only)
> > /OVER
> > /[NO]SHARE
> > /[NO]SYSTEM

> The following qualifiers affect what output is displayed when a tracepoint is reached:

> > /[NO]SILENT
> > /[NO]SOURCE

> The following qualifiers affect the timing and duration of tracepoints:

> > /AFTER:n
> > /TEMPORARY

> Use the /MODIFY qualifier to monitor changes at program locations (typically changes in the values of variables).

> If you set a tracepoint at a location currently used as a breakpoint, the breakpoint is canceled in favor of the tracepoint, and conversely.

> Tracepoints can be user defined or predefined. User-defined tracepoints are set explicitly with the SET TRACE command. Predefined tracepoints, which depend on the type of program you are debugging (for example, Ada or multiprocess), are established automatically when you start the debugger. Use the SHOW TRACE command to identify all tracepoints that are currently set. Any predefined tracepoints are identified as such.

> User-defined and predefined tracepoints are set and canceled independently. For example, a location or event can have both a user-defined and a predefined tracepoint. Canceling the user-defined tracepoint does not affect the predefined tracepoint, and conversely.

> Related commands:

> > (ACTIVATE,DEACTIVATE,SHOW,CANCEL) TRACE
> > CANCEL ALL
> > GO
> > SET BREAK
> > (SET,SHOW) EVENT_FACILITY
> > SET STEP [NO]SOURCE
> > SET WATCH

### Examples

#1
    DBG> SET TRACE SUB3

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