Debugging with GDB: Breakpoints In Guile

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#### 23.4.3.19 Manipulating breakpoints using Guile

Breakpoints in Guile are represented by objects of type `<gdb:breakpoint>`. New breakpoints can be created with the `make-breakpoint` Guile function, and then added to GDB with the `register-breakpoint!` Guile function. This two-step approach is taken to separate out the side-effect of adding the breakpoint to GDB from `make-breakpoint`.

Support is also provided to view and manipulate breakpoints created outside of Guile.

The following breakpoint-related procedures are provided by the `(gdb)` module:

Scheme Procedure: make-breakpoint location [#:type type] [#:wp-class wp-class] [#:internal internal] [#:temporary temporary]

  Create a new breakpoint at location, a string naming the location of the breakpoint, or an expression that defines a watchpoint. The contents can be any location recognized by the `break` command, or in the case of a watchpoint, by the `watch` command.

  The breakpoint is initially marked as ‘`invalid`’. The breakpoint is not usable until it has been registered with GDB with `register-breakpoint!`, at which point it becomes ‘`valid`’. The result is the `<gdb:breakpoint>` object representing the breakpoint.

  The optional type denotes the breakpoint to create. This argument can be either `BP_BREAKPOINT` or `BP_WATCHPOINT`, and defaults to `BP_BREAKPOINT`.

  The optional wp-class argument defines the class of watchpoint to create, if type is `BP_WATCHPOINT`. If a watchpoint class is not provided, it is assumed to be a `WP_WRITE` class.

  The optional internal argument allows the breakpoint to become invisible to the user. The breakpoint will neither be reported when registered, nor will it be listed in the output from `info breakpoints` (but will be listed with the `maint info breakpoints` command). If an internal flag is not provided, the breakpoint is visible (non-internal).

  The optional temporary argument makes the breakpoint a temporary breakpoint. Temporary breakpoints are deleted after they have been hit, after which the Guile breakpoint is no longer usable (although it may be re-registered with `register-breakpoint!`).

  When a watchpoint is created, GDB will try to create a hardware assisted watchpoint. If successful, the type of the watchpoint is changed from `BP_WATCHPOINT` to `BP_HARDWARE_WATCHPOINT` for `WP_WRITE`, `BP_READ_WATCHPOINT` for `WP_READ`, and `BP_ACCESS_WATCHPOINT` for `WP_ACCESS`. If not successful, the type of the watchpoint is left as `WP_WATCHPOINT`.

  The available types are represented by constants defined in the `gdb` module:

  `BP_BREAKPOINT`

    Normal code breakpoint.

  `BP_WATCHPOINT`

    Watchpoint breakpoint.

  `BP_HARDWARE_WATCHPOINT`

    Hardware assisted watchpoint. This value cannot be specified when creating the breakpoint.

  `BP_READ_WATCHPOINT`

    Hardware assisted read watchpoint. This value cannot be specified when creating the breakpoint.

  `BP_ACCESS_WATCHPOINT`

    Hardware assisted access watchpoint. This value cannot be specified when creating the breakpoint.

  `BP_CATCHPOINT`

    Catchpoint. This value cannot be specified when creating the breakpoint.

  The available watchpoint types are represented by constants defined in the `(gdb)` module:

  `WP_READ`

    Read only watchpoint.

  `WP_WRITE`

    Write only watchpoint.

  `WP_ACCESS`

    Read/Write watchpoint.

Scheme Procedure: register-breakpoint! breakpoint

  Add breakpoint, a `<gdb:breakpoint>` object, to GDB’s list of breakpoints. The breakpoint must have been created with `make-breakpoint`. One cannot register breakpoints that have been created outside of Guile. Once a breakpoint is registered it becomes ‘`valid`’. It is an error to register an already registered breakpoint. The result is unspecified.

Scheme Procedure: delete-breakpoint! breakpoint

  Remove breakpoint from GDB’s list of breakpoints. This also invalidates the Guile breakpoint object. Any further attempt to access the object will throw an exception.

  If breakpoint was created from Guile with `make-breakpoint` it may be re-registered with GDB, in which case the breakpoint becomes valid again.

Scheme Procedure: breakpoints

  Return a list of all breakpoints. Each element of the list is a `<gdb:breakpoint>` object.

Scheme Procedure: breakpoint? object

  Return `#t` if object is a `<gdb:breakpoint>` object, and `#f` otherwise.

Scheme Procedure: breakpoint-valid? breakpoint

  Return `#t` if breakpoint is valid, `#f` otherwise. Breakpoints created with `make-breakpoint` are marked as invalid until they are registered with GDB with `register-breakpoint!`. A `<gdb:breakpoint>` object can become invalid if the user deletes the breakpoint. In this case, the object still exists, but the underlying breakpoint does not. In the cases of watchpoint scope, the watchpoint remains valid even if execution of the inferior leaves the scope of that watchpoint.

Scheme Procedure: breakpoint-number breakpoint

  Return the breakpoint’s number — the identifier used by the user to manipulate the breakpoint.

Scheme Procedure: breakpoint-temporary? breakpoint

  Return `#t` if the breakpoint was created as a temporary breakpoint. Temporary breakpoints are automatically deleted after they’ve been hit. Calling this procedure, and all other procedures other than `breakpoint-valid?` and `register-breakpoint!`, will result in an error after the breakpoint has been hit (since it has been automatically deleted).

Scheme Procedure: breakpoint-type breakpoint

  Return the breakpoint’s type — the identifier used to determine the actual breakpoint type or use-case.

Scheme Procedure: breakpoint-visible? breakpoint

  Return `#t` if the breakpoint is visible to the user when hit, or when the ‘`info breakpoints`’ command is run. Otherwise return `#f`.

Scheme Procedure: breakpoint-location breakpoint

  Return the location of the breakpoint, as specified by the user. It is a string. If the breakpoint does not have a location (that is, it is a watchpoint) return `#f`.

Scheme Procedure: breakpoint-expression breakpoint

  Return the breakpoint expression, as specified by the user. It is a string. If the breakpoint does not have an expression (the breakpoint is not a watchpoint) return `#f`.

Scheme Procedure: breakpoint-enabled? breakpoint

  Return `#t` if the breakpoint is enabled, and `#f` otherwise.

Scheme Procedure: set-breakpoint-enabled! breakpoint flag

  Set the enabled state of breakpoint to flag. If flag is `#f` it is disabled, otherwise it is enabled.

Scheme Procedure: breakpoint-silent? breakpoint

  Return `#t` if the breakpoint is silent, and `#f` otherwise.

  Note that a breakpoint can also be silent if it has commands and the first command is `silent`. This is not reported by the `silent` attribute.

Scheme Procedure: set-breakpoint-silent! breakpoint flag

  Set the silent state of breakpoint to flag. If flag is `#f` the breakpoint is made silent, otherwise it is made non-silent (or noisy).

Scheme Procedure: breakpoint-ignore-count breakpoint

  Return the ignore count for breakpoint.

Scheme Procedure: set-breakpoint-ignore-count! breakpoint count

  Set the ignore count for breakpoint to count.

Scheme Procedure: breakpoint-hit-count breakpoint

  Return hit count of breakpoint.

Scheme Procedure: set-breakpoint-hit-count! breakpoint count

  Set the hit count of breakpoint to count. At present, count must be zero.

Scheme Procedure: breakpoint-thread breakpoint

  Return the global-thread-id for thread-specific breakpoint breakpoint. Return #f if breakpoint is not thread-specific.

Scheme Procedure: set-breakpoint-thread! breakpoint global-thread-id|#f

  Set the thread-id for breakpoint to global-thread-id If set to `#f`, the breakpoint is no longer thread-specific.

Scheme Procedure: breakpoint-task breakpoint

  If the breakpoint is Ada task-specific, return the Ada task id. If the breakpoint is not task-specific (or the underlying language is not Ada), return `#f`.

Scheme Procedure: set-breakpoint-task! breakpoint task

  Set the Ada task of breakpoint to task. If set to `#f`, the breakpoint is no longer task-specific.

Scheme Procedure: breakpoint-condition breakpoint

  Return the condition of breakpoint, as specified by the user. It is a string. If there is no condition, return `#f`.

Scheme Procedure: set-breakpoint-condition! breakpoint condition

  Set the condition of breakpoint to condition, which must be a string. If set to `#f` then the breakpoint becomes unconditional.

Scheme Procedure: breakpoint-stop breakpoint

  Return the stop predicate of breakpoint. See `set-breakpoint-stop!` below in this section.

Scheme Procedure: set-breakpoint-stop! breakpoint procedure|#f

  Set the stop predicate of breakpoint. The predicate procedure takes one argument: the <gdb:breakpoint> object. If this predicate is set to a procedure then it is invoked whenever the inferior reaches this breakpoint. If it returns `#t`, or any non-`#f` value, then the inferior is stopped, otherwise the inferior will continue.

  If there are multiple breakpoints at the same location with a `stop` predicate, each one will be called regardless of the return status of the previous. This ensures that all `stop` predicates have a chance to execute at that location. In this scenario if one of the methods returns `#t` but the others return `#f`, the inferior will still be stopped.

  You should not alter the execution state of the inferior (i.e., step, next, etc.), alter the current frame context (i.e., change the current active frame), or alter, add or delete any breakpoint. As a general rule, you should not alter any data within GDB or the inferior at this time.

  Example `stop` implementation:

      (define (my-stop? bkpt)
        (let ((int-val (parse-and-eval "foo")))
          (value=? int-val 3)))
      (define bkpt (make-breakpoint "main.c:42"))
      (register-breakpoint! bkpt)
      (set-breakpoint-stop! bkpt my-stop?)

Scheme Procedure: breakpoint-commands breakpoint

  Return the commands attached to breakpoint as a string, or `#f` if there are none.

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