Next: , Previous: , Up: Python API   [Contents][Index]


23.2.2.25 Manipulating breakpoints using Python

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

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

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 temporary argument makes the breakpoint a temporary breakpoint. Temporary breakpoints are deleted after they have been hit. Any further access to the Python breakpoint after it has been hit will result in a runtime error (as that breakpoint has now been automatically deleted). 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 in 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.

Variable: Breakpoint.temporary

This attribute indicates whether the breakpoint was created as a temporary breakpoint. Temporary breakpoints are automatically deleted after that breakpoint has been hit. Access to this attribute, and all other attributes and functions other than the is_valid function, will result in an error after the breakpoint has been hit (as it has been automatically deleted). 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.


Next: , Previous: , Up: Python API   [Contents][Index]