Breakpoints In Python - Debugging with GDB
Description: Debugging with GDB

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##### 23.2.2.21 Manipulating breakpoints using Python

Python code can manipulate breakpoints via the `gdb.Breakpoint` class.

— Function: Breakpoint.__init__ (spec [, type [, wp_class [,internal]]])

> Create a new breakpoint. spec is 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 optional type denotes the breakpoint to create from the types defined later in this chapter. This argument can be either: `gdb.BP_BREAKPOINT` or `gdb.BP_WATCHPOINT`. type defaults to `gdb.BP_BREAKPOINT`. The optional internal argument allows the breakpoint to become invisible to the user. The breakpoint will neither be reported when created, nor will it be listed in the output from `info breakpoints` (but will be listed with the `maint info breakpoints` command). The optional wp_class argument defines the class of watchpoint to create, if type is `gdb.BP_WATCHPOINT`. If a watchpoint class is not provided, it is assumed to be a `gdb.WP_WRITE` class.

— Function: Breakpoint.stop (self)

> The `gdb.Breakpoint` class can be sub-classed and, in particular, you may choose to implement the `stop` method. If this method is defined as a sub-class of `gdb.Breakpoint`, it will be called when the inferior reaches any location of a breakpoint which instantiates that sub-class. If the method returns `True`, the inferior will be stopped at the location of the breakpoint, otherwise the inferior will continue.

> If there are multiple breakpoints at the same location with a `stop` method, each one will be called regardless of the return status of the previous. This ensures that all `stop` methods have a chance to execute at that location. In this scenario if one of the methods returns `True` but the others return `False`, 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:

>               class MyBreakpoint (gdb.Breakpoint):
>                     def stop (self):
>                       inf_val = gdb.parse_and_eval("foo")
>                       if inf_val == 3:
>                         return True
>                       return False

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

`gdb.WP_READ`
  Read only watchpoint.

`gdb.WP_WRITE`
  Write only watchpoint.

`gdb.WP_ACCESS`
  Read/Write watchpoint.

— Function: Breakpoint.is_valid ()

> Return `True` if this `Breakpoint` object is valid, `False` otherwise. A `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.

— Function: Breakpoint.delete

> Permanently deletes the gdb breakpoint. This also invalidates the Python `Breakpoint` object. Any further access to this object's attributes or methods will raise an error.

— Variable: Breakpoint.enabled

> This attribute is `True` if the breakpoint is enabled, and `False` otherwise. This attribute is writable.

— Variable: Breakpoint.silent

> This attribute is `True` if the breakpoint is silent, and `False` otherwise. This attribute is writable.

> 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.

— Variable: Breakpoint.thread

> If the breakpoint is thread-specific, this attribute holds the thread id. If the breakpoint is not thread-specific, this attribute is `None`. This attribute is writable.

— Variable: Breakpoint.task

> If the breakpoint is Ada task-specific, this attribute holds the Ada task id. If the breakpoint is not task-specific (or the underlying language is not Ada), this attribute is `None`. This attribute is writable.

— Variable: Breakpoint.ignore_count

> This attribute holds the ignore count for the breakpoint, an integer. This attribute is writable.

— Variable: Breakpoint.number

> This attribute holds the breakpoint's number — the identifier used by the user to manipulate the breakpoint. This attribute is not writable.

— Variable: Breakpoint.type

> This attribute holds the breakpoint's type — the identifier used to determine the actual breakpoint type or use-case. This attribute is not writable.

— Variable: Breakpoint.visible

> This attribute tells whether the breakpoint is visible to the user when set, or when the ‘`info breakpoints`’ command is run. This attribute is not writable.

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

`gdb.BP_BREAKPOINT`
  Normal code breakpoint.

`gdb.BP_WATCHPOINT`
  Watchpoint breakpoint.

`gdb.BP_HARDWARE_WATCHPOINT`
  Hardware assisted watchpoint.

`gdb.BP_READ_WATCHPOINT`
  Hardware assisted read watchpoint.

`gdb.BP_ACCESS_WATCHPOINT`
  Hardware assisted access watchpoint.

— Variable: Breakpoint.hit_count

> This attribute holds the hit count for the breakpoint, an integer. This attribute is writable, but currently it can only be set to zero.

— Variable: Breakpoint.location

> This attribute holds 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) the attribute's value is `None`. This attribute is not writable.

— Variable: Breakpoint.expression

> This attribute holds a 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) the attribute's value is `None`. This attribute is not writable.

— Variable: Breakpoint.condition

> This attribute holds the condition of the breakpoint, as specified by the user. It is a string. If there is no condition, this attribute's value is `None`. This attribute is writable.

— Variable: Breakpoint.commands

> This attribute holds the commands attached to the breakpoint. If there are commands, this attribute's value is a string holding all the commands, separated by newlines. If there are no commands, this attribute is `None`. This attribute is not writable.