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binutils-gdb/gdb/observable.h
Andrew Burgess 59912fb2d2 gdb: add Python events for program space addition and removal 
Initially I just wanted a Python event for when GDB removes a program
space, I'm writing a Python extension that caches information for each
program space, and need to know when I should discard entries for a
particular program space.

But, it seemed easy enough to also add an event for when GDB adds a
new program space, so I went ahead and added both new events.

Of course, we don't currently have an observable for program space
addition or removal, so I first needed to add these.  After that it's
pretty simple to add two new Python events and have these trigger.

The two new event registries are:

  events.new_progspace
  events.free_progspace

These emit NewProgspaceEvent and FreeProgspaceEvent objects
respectively, each of these new event types has a 'progspace'
attribute that contains the relevant gdb.Progspace object.

There's a couple of things to be mindful of.

First, it is not possible to catch the NewProgspaceEvent for the very
first program space, the one that is created when GDB first starts, as
this program space is created before any Python scripts are sourced.

In order to allow this event to be caught we would need to defer
creating the first program space, and as a consequence the first
inferior, until some later time.  But, existing scripts could easily
depend on there being an initial inferior, so I really don't think we
should change that -- and so, we end up with the consequence that we
can't catch the event for the first program space.

The second, I think minor, issue, is that GDB doesn't clean up its
program spaces upon exit -- or at least, they are not cleaned up
before Python is shut down.  As a result, any program spaces in use at
the time GDB exits don't generate a FreeProgspaceEvent.  I'm not
particularly worried about this for my use case, I'm using the event
to ensure that a cache doesn't hold stale entries within a single GDB
session.  It's also easy enough to add a Python at-exit callback which
can do any final cleanup if needed.

Finally, when testing, I did hit a slightly weird issue with some of
the remote boards (e.g. remote-stdio-gdbserver).  As a consequence of
this issue I see some output like this in the gdb.log:

  (gdb) PASS: gdb.python/py-progspace-events.exp: inferior 1
  step
  FreeProgspaceEvent: <gdb.Progspace object at 0x7fb7e1d19c10>
  warning: cannot close "target:/lib64/libm.so.6": Cannot execute this command while the target is running.
  Use the "interrupt" command to stop the target
  and then try again.
  warning: cannot close "target:/lib64/libc.so.6": Cannot execute this command while the target is running.
  Use the "interrupt" command to stop the target
  and then try again.
  warning: cannot close "target:/lib64/ld-linux-x86-64.so.2": Cannot execute this command while the target is running.
  Use the "interrupt" command to stop the target
  and then try again.
  do_parent_stuff () at py-progspace-events.c:41
  41        ++global_var;
  (gdb) PASS: gdb.python/py-progspace-events.exp: step

The 'FreeProgspaceEvent ...' line is expected, that's my test Python
extension logging the event.  What isn't expected are all the blocks
like:

  warning: cannot close "target:/lib64/libm.so.6": Cannot execute this command while the target is running.
  Use the "interrupt" command to stop the target
  and then try again.

It turns out that this has nothing to do with my changes, this is just
a consequence of reading files over the remote protocol.  The test
forks a child process which GDB stays attached too.  When the child
exits, GDB cleans up by calling prune_inferiors, which in turn can
result in GDB trying to close some files that are open because of the
inferior being deleted.

If the prune_inferiors call occurs when the remote target is
running (and in non-async mode) then GDB will try to send a fileio
packet while the remote target is waiting for a stop reply, and the
remote target will throw an error, see remote_target::putpkt_binary in
remote.c for details.

I'm going to look at fixing this, but, as I said, this is nothing to
do with this change, I just mention it because I ended up needing to
account for these warning messages in one of my tests, and it all
looks a bit weird.

Approved-By: Tom Tromey <tom@tromey.com>
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
2023-10-02 17:06:40 +01:00

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/* Observers
Copyright (C) 2016-2023 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef OBSERVABLE_H
#define OBSERVABLE_H
#include "gdbsupport/observable.h"
#include "target/waitstatus.h"
struct bpstat;
struct so_list;
struct objfile;
struct thread_info;
struct inferior;
struct process_stratum_target;
struct target_ops;
struct trace_state_variable;
struct program_space;
namespace gdb
{
namespace observers
{
/* The inferior has stopped for real. The BS argument describes the
breakpoints were are stopped at, if any. Second argument
PRINT_FRAME non-zero means display the location where the
inferior has stopped.
gdb notifies all normal_stop observers when the inferior execution
has just stopped, the associated messages and annotations have been
printed, and the control is about to be returned to the user.
Note that the normal_stop notification is not emitted when the
execution stops due to a breakpoint, and this breakpoint has a
condition that is not met. If the breakpoint has any associated
commands list, the commands are executed after the notification is
emitted. */
extern observable<struct bpstat */* bs */, int /* print_frame */> normal_stop;
/* The inferior was stopped by a signal. */
extern observable<enum gdb_signal /* siggnal */> signal_received;
/* The target's register contents have changed. */
extern observable<struct target_ops */* target */> target_changed;
/* The executable being debugged by GDB in PSPACE has changed: The user
decided to debug a different program, or the program he was debugging
has been modified since being loaded by the debugger (by being
recompiled, for instance). The path to the new executable can be found
by examining PSPACE->exec_filename.
When RELOAD is true the path to the executable hasn't changed, but the
file does appear to have changed, so GDB reloaded it, e.g. if the user
recompiled the executable. when RELOAD is false then the path to the
executable has not changed. */
extern observable<struct program_space */* pspace */,
bool /*reload */> executable_changed;
/* gdb has just connected to an inferior. For 'run', gdb calls this
observer while the inferior is still stopped at the entry-point
instruction. For 'attach' and 'core', gdb calls this observer
immediately after connecting to the inferior, and before any
information on the inferior has been printed. */
extern observable<inferior */* inferior */> inferior_created;
/* The inferior EXEC_INF has exec'ed a new executable file.
Execution continues in FOLLOW_INF, which may or may not be the same as
EXEC_INF, depending on "set follow-exec-mode". */
extern observable<inferior */* exec_inf */, inferior */* follow_inf */>
inferior_execd;
/* The inferior PARENT_INF has forked. If we are setting up an inferior for
the child (because we follow only the child or we follow both), CHILD_INF
is the child inferior. Otherwise, CHILD_INF is nullptr.
FORK_KIND is TARGET_WAITKIND_FORKED or TARGET_WAITKIND_VFORKED. */
extern observable<inferior */* parent_inf */, inferior */* child_inf */,
target_waitkind /* fork_kind */> inferior_forked;
/* The shared library specified by SOLIB has been loaded. Note that
when gdb calls this observer, the library's symbols probably
haven't been loaded yet. */
extern observable<struct so_list */* solib */> solib_loaded;
/* The shared library SOLIB has been unloaded from program space PSPACE.
Note when gdb calls this observer, the library's symbols have not
been unloaded yet, and thus are still available. */
extern observable<struct program_space */* pspace */, struct so_list */* solib */>
solib_unloaded;
/* The symbol file specified by OBJFILE has been loaded. Called
with OBJFILE equal to NULL to indicate previously loaded symbol
table data has now been invalidated. */
extern observable<struct objfile */* objfile */> new_objfile;
/* The object file specified by OBJFILE is about to be freed. */
extern observable<struct objfile */* objfile */> free_objfile;
/* The thread specified by T has been created. */
extern observable<struct thread_info */* t */> new_thread;
/* The thread specified by T has exited. EXIT_CODE is the thread's
exit code, if available. The SILENT argument indicates that GDB is
removing the thread from its tables without wanting to notify the
CLI about it. */
extern observable<thread_info */* t */,
gdb::optional<ULONGEST> /* exit_code */,
bool /* silent */> thread_exit;
/* An explicit stop request was issued to PTID. If PTID equals
minus_one_ptid, the request applied to all threads. If
ptid_is_pid(PTID) returns true, the request applied to all
threads of the process pointed at by PTID. Otherwise, the
request applied to the single thread pointed at by PTID. */
extern observable<ptid_t /* ptid */> thread_stop_requested;
/* The target was resumed. The PTID parameter specifies which
thread was resume, and may be RESUME_ALL if all threads are
resumed. */
extern observable<ptid_t /* ptid */> target_resumed;
/* The target is about to be proceeded. */
extern observable<> about_to_proceed;
/* A new breakpoint B has been created. */
extern observable<struct breakpoint */* b */> breakpoint_created;
/* A breakpoint has been destroyed. The argument B is the
pointer to the destroyed breakpoint. */
extern observable<struct breakpoint */* b */> breakpoint_deleted;
/* A breakpoint has been modified in some way. The argument B
is the modified breakpoint. */
extern observable<struct breakpoint */* b */> breakpoint_modified;
/* The current architecture has changed. The argument NEWARCH is a
pointer to the new architecture. */
extern observable<struct gdbarch */* newarch */> architecture_changed;
/* The thread's ptid has changed. The OLD_PTID parameter specifies
the old value, and NEW_PTID specifies the new value. */
extern observable<process_stratum_target * /* target */,
ptid_t /* old_ptid */, ptid_t /* new_ptid */>
thread_ptid_changed;
/* The inferior INF has been added to the list of inferiors. At
this point, it might not be associated with any process. */
extern observable<struct inferior */* inf */> inferior_added;
/* The inferior identified by INF has been attached to a
process. */
extern observable<struct inferior */* inf */> inferior_appeared;
/* Inferior INF is about to be detached. */
extern observable<struct inferior */* inf */> inferior_pre_detach;
/* Either the inferior associated with INF has been detached from
the process, or the process has exited. */
extern observable<struct inferior */* inf */> inferior_exit;
/* The inferior INF has been removed from the list of inferiors.
This method is called immediately before freeing INF. */
extern observable<struct inferior */* inf */> inferior_removed;
/* The inferior CLONE has been created by cloning INF. */
extern observable<struct inferior */* inf */, struct inferior */* clone */>
inferior_cloned;
/* Bytes from DATA to DATA + LEN have been written to the inferior
at ADDR. */
extern observable<struct inferior */* inferior */, CORE_ADDR /* addr */,
ssize_t /* len */, const bfd_byte */* data */>
memory_changed;
/* Called before a top-level prompt is displayed. CURRENT_PROMPT is
the current top-level prompt. */
extern observable<const char */* current_prompt */> before_prompt;
/* Variable gdb_datadir has been set. The value may not necessarily
change. */
extern observable<> gdb_datadir_changed;
/* An inferior function at ADDRESS is about to be called in thread
THREAD. */
extern observable<ptid_t /* thread */, CORE_ADDR /* address */>
inferior_call_pre;
/* The inferior function at ADDRESS has just been called. This
observer is called even if the inferior exits during the call.
THREAD is the thread in which the function was called, which may
be different from the current thread. */
extern observable<ptid_t /* thread */, CORE_ADDR /* address */>
inferior_call_post;
/* A register in the inferior has been modified by the gdb user. */
extern observable<frame_info_ptr /* frame */, int /* regnum */>
register_changed;
/* The user-selected inferior, thread and/or frame has changed. The
user_select_what flag specifies if the inferior, thread and/or
frame has changed. */
extern observable<user_selected_what /* selection */>
user_selected_context_changed;
/* This is notified when a styling setting has changed, content may need
to be updated based on the new settings. */
extern observable<> styling_changed;
/* The CLI's notion of the current source has changed. This differs
from user_selected_context_changed in that it is also set by the
"list" command. */
extern observable<> current_source_symtab_and_line_changed;
/* Called when GDB is about to exit. */
extern observable<int> gdb_exiting;
/* When a connection is removed. */
extern observable<process_stratum_target */* target */> connection_removed;
/* About to enter target_wait (). */
extern observable <ptid_t /* ptid */> target_pre_wait;
/* About to leave target_wait (). */
extern observable <ptid_t /* event_ptid */> target_post_wait;
/* New program space PSPACE was created. */
extern observable <program_space */* pspace */> new_program_space;
/* The program space PSPACE is about to be deleted. */
extern observable <program_space */* pspace */> free_program_space;
} /* namespace observers */
} /* namespace gdb */
#endif /* OBSERVABLE_H */
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