Gdb/Events-In-Python
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23.2.2.17 Events In Python
GDB provides a general event facility so that Python code can be notified of various state changes, particularly changes that occur in the inferior.
An event is just an object that describes some state change. The type of the object and its attributes will vary depending on the details of the change. All the existing events are described below.
In order to be notified of an event, you must register an event handler
with an event registry. An event registry is an object in the
gdb.events
module which dispatches particular events. A registry
provides methods to register and unregister event handlers:
- Function
- EventRegistry.connect (object)
- Add the given callable
object
to the registry. This object will be called when an event corresponding to this registry occurs.
- Function
- EventRegistry.disconnect (object)
- Remove the given
object
from the registry. Once removed, the object will no longer receive notifications of events.
Here is an example:
def exit_handler (event): print "event type: exit" print "exit code: %d" % (event.exit_code) gdb.events.exited.connect (exit_handler)
In the above example we connect our handler exit_handler
to the
registry events.exited
. Once connected, exit_handler
gets
called when the inferior exits. The argument event in this example is
of type gdb.ExitedEvent
. As you can see in the example the
ExitedEvent
object has an attribute which indicates the exit code of
the inferior.
The following is a listing of the event registries that are available and details of the events they emit:
events.cont
Emits
gdb.ThreadEvent
.Some events can be thread specific when GDB is running in non-stop mode. When represented in Python, these events all extend
gdb.ThreadEvent
. Note, this event is not emitted directly; instead, events which are emitted by this or other modules might extend this event. Examples of these events aregdb.BreakpointEvent
andgdb.ContinueEvent
.- Variable: ThreadEvent.inferior_thread
In non-stop mode this attribute will be set to the specific thread which was involved in the emitted event. Otherwise, it will be set to
None
.
Emits
gdb.ContinueEvent
which extendsgdb.ThreadEvent
.This event indicates that the inferior has been continued after a stop. For inherited attribute refer to
gdb.ThreadEvent
above.events.exited
Emits
events.ExitedEvent
which indicates that the inferior has exited.events.ExitedEvent
has two attributes:- Variable: ExitedEvent.exit_code
An integer representing the exit code, if available, which the inferior has returned. (The exit code could be unavailable if, for example, GDB detaches from the inferior.) If the exit code is unavailable, the attribute does not exist.
- Variable: ExitedEvent.inferior
A reference to the inferior which triggered the
exited
event.
events.stop
Emits
gdb.StopEvent
which extendsgdb.ThreadEvent
.Indicates that the inferior has stopped. All events emitted by this registry extend StopEvent. As a child of
gdb.ThreadEvent
,gdb.StopEvent
will indicate the stopped thread when GDB is running in non-stop mode. Refer togdb.ThreadEvent
above for more details.Emits
gdb.SignalEvent
which extendsgdb.StopEvent
.This event indicates that the inferior or one of its threads has received as signal.
gdb.SignalEvent
has the following attributes:- Variable: SignalEvent.stop_signal
A string representing the signal received by the inferior. A list of possible signal values can be obtained by running the command
info signals
in the GDB command prompt.
Also emits
gdb.BreakpointEvent
which extendsgdb.StopEvent
.gdb.BreakpointEvent
event indicates that one or more breakpoints have been hit, and has the following attributes:- Variable: BreakpointEvent.breakpoints
A sequence containing references to all the breakpoints (type
gdb.Breakpoint
) that were hit. See Breakpoints In Python, for details of thegdb.Breakpoint
object.
- Variable: BreakpointEvent.breakpoint
A reference to the first breakpoint that was hit. This function is maintained for backward compatibility and is now deprecated in favor of the
gdb.BreakpointEvent.breakpoints
attribute.
events.new_objfile
Emits
gdb.NewObjFileEvent
which indicates that a new object file has been loaded by GDB.gdb.NewObjFileEvent
has one attribute:- Variable: NewObjFileEvent.new_objfile
A reference to the object file (
gdb.Objfile
) which has been loaded. See Objfiles In Python, for details of thegdb.Objfile
object.
events.clear_objfiles
Emits
gdb.ClearObjFilesEvent
which indicates that the list of object files for a program space has been reset.gdb.ClearObjFilesEvent
has one attribute:- Variable: ClearObjFilesEvent.progspace
A reference to the program space (
gdb.Progspace
) whose objfile list has been cleared. See Progspaces In Python.
events.inferior_call
Emits events just before and after a function in the inferior is called by GDB. Before an inferior call, this emits an event of type
gdb.InferiorCallPreEvent
, and after an inferior call, this emits an event of typegdb.InferiorCallPostEvent
.gdb.InferiorCallPreEvent
Indicates that a function in the inferior is about to be called.
- Variable: InferiorCallPreEvent.ptid
The thread in which the call will be run.
- Variable: InferiorCallPreEvent.address
The location of the function to be called.
gdb.InferiorCallPostEvent
Indicates that a function in the inferior has just been called.
- Variable: InferiorCallPostEvent.ptid
The thread in which the call was run.
- Variable: InferiorCallPostEvent.address
The location of the function that was called.
events.memory_changed
Emits gdb.MemoryChangedEvent
which indicates that the memory of the
inferior has been modified by the GDB user, for instance via a
command like set *addr = value
. The event has the following
attributes:
- Variable
- MemoryChangedEvent.address
- The start address of the changed region.
- Variable
- MemoryChangedEvent.length
- Length in bytes of the changed region.
events.register_changed
Emits gdb.RegisterChangedEvent
which indicates that a register in the
inferior has been modified by the GDB user.
- Variable
- RegisterChangedEvent.frame
- A gdb.Frame object representing the frame in which the register was modified.
- Variable
- RegisterChangedEvent.regnum
- Denotes which register was modified.
events.breakpoint_created
This is emitted when a new breakpoint has been created. The argument
that is passed is the new gdb.Breakpoint
object.
events.breakpoint_modified
This is emitted when a breakpoint has been modified in some way. The
argument that is passed is the new gdb.Breakpoint
object.
events.breakpoint_deleted
This is emitted when a breakpoint has been deleted. The argument that
is passed is the gdb.Breakpoint
object. When this event is
emitted, the gdb.Breakpoint
object will already be in its
invalid state; that is, the is_valid
method will return
False
.
events.before_prompt
This event carries no payload. It is emitted each time GDB presents a prompt to the user.
events.new_inferior
This is emitted when a new inferior is created. Note that the inferior is not necessarily running; in fact, it may not even have an associated executable.
The event is of type gdb.NewInferiorEvent
. This has a single
attribute:
- Variable
- NewInferiorEvent.inferior
- The new inferior, a
gdb.Inferior
object.
events.inferior_deleted
This is emitted when an inferior has been deleted. Note that this is
not the same as process exit; it is notified when the inferior itself
is removed, say via remove-inferiors
.
The event is of type gdb.InferiorDeletedEvent
. This has a single
attribute:
- Variable
- NewInferiorEvent.inferior
- The inferior that is being removed, a
gdb.Inferior
object.
events.new_thread
This is emitted when GDB notices a new thread. The event is of
type gdb.NewThreadEvent
, which extends gdb.ThreadEvent
.
This has a single attribute:
- Variable
- NewThreadEvent.inferior_thread
- The new thread.
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