Sun Studio 12: Debugging a Program With dbx

Using Predefined Variables

Certain read-only ksh predefined variables are provided. The following variables are always valid:

Variable	Definition
`$ins`	Disassembly of the current instruction.
`$lineno`	Current line number in decimal.
`$vlineno`	Current “visiting” line number in decimal.
`$line`	Contents of the current line.
`$func`	Name of the current function.
`$vfunc`	Name of the current “visiting” function.
`$class`	Name of the class to which `$func` belongs.
`$vclass`	Name of the class to which `$vfunc` belongs.
`$file`	Name of the current file.
`$vfile`	Name of the current file being visited.
`$loadobj`	Name of the current loadable object.
`$vloadobj`	Name of the current loadable object being visited.
`$scope`	Scope of the current PC in back-quote notation.
`$vscope`	Scope of the visited PC in back-quote notation.
`$funcaddr`	Address of `$func` in hex.
`$caller`	Name of the function calling `$func.`
`$dllist`	After a `dlopen` or `dlclose` event, contains the list of load objects just loaded or unloaded. The first word of `dllist` is a “+” or a “-” depending on whether a `dlopen` or a `dlclose` has occurred.
`$newhandlerid`	ID of the most recently created handler. This variable has an undefined value after any command that deletes handlers. Use the variable immediately after creating a handler. `dbx` cannot capture all of the handler IDs for a command that creates multiple handlers.
`$firedhandlers`	List of handler ids that caused the most recent stoppage. The handlers on the list are marked with “*” in the output of the `status` command.
`$proc`	Process ID of the current process being debugged.
`$lwp`	Lwp ID of the current LWP.
`$thread`	Thread ID of the current thread.
`$newlwp`	lwp ID of a newly created LWP.
`$newthread`	Thread ID of a newly created thread.
`$prog`	Full path name of the program being debugged.
`$oprog`	Previous value of `$prog`, which is used to get back to what you were debugging following an `exec()`, when `$prog` reverts to “-”. While `$prog` is expanded to a full path name, `$oprog` contains the program path as specified on the command line or to the `debug` command. If `exec()` is called more than once, there is no way to return to the original program.
`$exec32`	True if the `dbx` binary is 32–bit.
`$exitcode`	Exit status from the last run of the program. The value is an empty string if the process has not exited.

As an example, consider that whereami can be implemented as:

function whereami {
  echo Stopped in $func at line $lineno in file $(basename $file)
  echo "$lineno\t$line"
}

Variables Valid for `when` Command

The following variables are valid only within the body of a when command.

`$handlerid`

During the execution of the body, $handlerid is the id of the when command to which the body belongs. These commands are equivalent:

when X -temp { do_stuff; }
when X  { do_stuff; delete $handlerid; }

`$booting`

$booting is set to true if the event occurs during the boot process. Whenever a new program is debugged, it is first run without the user’s knowledge so that the list and location of shared libraries can be ascertained. The process is then killed. This sequence is termed booting.

While booting is occurring, all events are still available. Use this variable to distinguish the sync and the syncrtld events occurring during a debug and the ones occurring during a normal run.

Variables Valid for Specific Events

Certain variables are valid only for specific events as shown in the following tables.

Table B–1 Variables Valid for sig Event


Variable	Description
`$sig`	Signal number that caused the event
`$sigstr`	Name of `$sig`
`$sigcode`	Subcode of `$sig` if applicable
`$sigcodestr`	Name of `$sigcode`
`$sigsender`	Process ID of sender of the signal, if appropriate

Table B–2 Variable Valid for exit Event


Variable	Description
`$exitcode`	Value of the argument passed to `_exit(2)` or `exit(3)` or the return value of `main`

Table B–3 Variable Valid for dlopen and dlclose Events


Variable	Description
`$dlobj`	Pathname of the load object dlopened or dlclosed

Table B–4 Variables Valid for sysin and sysout Events


Variable	Description
`$syscode`	System call number
`$sysname`	System call name

Table B–5 Variable Valid for proc_gone Events


Variable	Description
`$reason`	One of signal, exit, kill, or detach

Table B–6 Variables Valid for thr_create Event


Variable	Description
`$newthread`	Id of the newly created thread (for example, `t@5`)
`$newlwp`	Id of the newly created LWP (for example, `l@4`)

Using Predefined Variables

Variables Valid for when Command

$handlerid

$booting

Variables Valid for Specific Events

Variables Valid for `when` Command

`$handlerid`

`$booting`