gdb/python: make the executable_changed event available from Python

This commit makes the executable_changed observable available through
the Python API as an event.  There's nothing particularly interesting
going on here, it just follows the same pattern as many of the other
Python events we support.

The new event registry is called events.executable_changed, and this
emits an ExecutableChangedEvent object which has two attributes, a
gdb.Progspace called 'progspace', this is the program space in which
the executable changed, and a Boolean called 'reload', which is True
if the same executable changed on disk and has been reloaded, or is
False when a new executable has been loaded.

One interesting thing did come up during testing though, you'll notice
the test contains a setup_kfail call.  During testing I observed that
the executable_changed event would trigger twice when GDB restarted an
inferior.  However, the ExecutableChangedEvent object is identical for
both calls, so the wrong information is never sent out, we just see
one too many events.

I tracked this down to how the reload_symbols function (symfile.c)
takes care to also reload the executable, however, I've split fixing
this into a separate commit, so see the next commit for details.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-By: Tom Tromey <tom@tromey.com>

6 files changed, 198 insertions, 0 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 2d57f52..fd7ab28 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -310,6 +310,11 @@ show tui mouse-events
      file name will have been partially resolved to an absolute file
      name.
 
+  ** A new executable_changed event registry is available.  This event
+     emits ExecutableChangedEvent objects, which have 'progspace' (a
+     gdb.Progspace) and 'reload' (a Boolean) attributes.  This event
+     is emitted when gdb.Progspace.executable_filename changes.
+
 *** Changes in GDB 13
 
 * MI version 1 is deprecated, and will be removed in GDB 14.
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index 4c8bb12..0471e78 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -3929,6 +3929,39 @@ This is emitted when @value{GDBN} removes a connection
 The @code{gdb.TargetConnection} that is being removed.
 @end defvar
 
+@item events.executable_changed
+Emits @code{gdb.ExecutableChangedEvent} which indicates that the
+@code{gdb.Progspace.executable_filename} has changed.
+
+This event is emitted when either the value of
+@code{gdb.Progspace.executable_filename } has changed to name a
+different file, or the executable file named by
+@code{gdb.Progspace.executable_filename} has changed on disk, and
+@value{GDBN} has therefore reloaded it.
+
+@defvar ExecutableChangedEvent.progspace
+The @code{gdb.Progspace} in which the current executable has changed.
+The file name of the updated executable will be visible in
+@code{gdb.Progspace.executable_filename} (@pxref{Progspaces In Python}).
+@end defvar
+@defvar ExecutableChangedEvent.reload
+This attribute will be @code{True} if the value of
+@code{gdb.Progspace.executable_filename} didn't change, but the file
+it names changed on disk instead, and @value{GDBN} reloaded it.
+
+When this attribute is @code{False}, the value in
+@code{gdb.Progspace.executable_filename} was changed to name a
+different file.
+@end defvar
+
+Remember that @value{GDBN} tracks the executable file and the symbol
+file separately, these are visible as
+@code{gdb.Progspace.executable_filename} and
+@code{gdb.Progspace.filename} respectively.  When using the @kbd{file}
+command, @value{GDBN} updates both of these fields, but the executable
+file is updated first, so when this event is emitted, the executable
+filename will have changed, but the symbol filename might still hold
+its previous value.
 @end table
 
 @node Threads In Python
diff --git a/gdb/python/py-all-events.def b/gdb/python/py-all-events.def
index aa28f2c..04a12e1 100644
--- a/gdb/python/py-all-events.def
+++ b/gdb/python/py-all-events.def
@@ -42,3 +42,4 @@ GDB_PY_DEFINE_EVENT(breakpoint_modified)
 GDB_PY_DEFINE_EVENT(before_prompt)
 GDB_PY_DEFINE_EVENT(gdb_exiting)
 GDB_PY_DEFINE_EVENT(connection_removed)
+GDB_PY_DEFINE_EVENT(executable_changed)
diff --git a/gdb/python/py-event-types.def b/gdb/python/py-event-types.def
index 395d6c0..b862094 100644
--- a/gdb/python/py-event-types.def
+++ b/gdb/python/py-event-types.def
@@ -125,3 +125,8 @@ GDB_PY_DEFINE_EVENT_TYPE (connection,
 			  "ConnectionEvent",
 			  "GDB connection added or removed object",
 			  event_object_type);
+
+GDB_PY_DEFINE_EVENT_TYPE (executable_changed,
+			  "ExecutableChangedEvent",
+			  "GDB executable changed event",
+			  event_object_type);
diff --git a/gdb/python/py-progspace.c b/gdb/python/py-progspace.c
index 1319978..082509b 100644
--- a/gdb/python/py-progspace.c
+++ b/gdb/python/py-progspace.c
@@ -26,6 +26,8 @@
 #include "arch-utils.h"
 #include "solib.h"
 #include "block.h"
+#include "py-event.h"
+#include "observable.h"
 
 struct pspace_object
 {
@@ -592,9 +594,61 @@ gdbpy_is_progspace (PyObject *obj)
   return PyObject_TypeCheck (obj, &pspace_object_type);
 }
 
+/* Emit an ExecutableChangedEvent event to REGISTRY.  Return 0 on success,
+   or a negative value on error.  PSPACE is the program_space in which the
+   current executable has changed, and RELOAD_P is true if the executable
+   path stayed the same, but the file on disk changed, or false if the
+   executable path actually changed.  */
+
+static int
+emit_executable_changed_event (eventregistry_object *registry,
+			       struct program_space *pspace, bool reload_p)
+{
+  gdbpy_ref<> event_obj
+    = create_event_object (&executable_changed_event_object_type);
+  if (event_obj == nullptr)
+    return -1;
+
+  gdbpy_ref<> py_pspace = pspace_to_pspace_object (pspace);
+  if (py_pspace == nullptr
+      || evpy_add_attribute (event_obj.get (), "progspace",
+			     py_pspace.get ()) < 0)
+    return -1;
+
+  gdbpy_ref<> py_reload_p (PyBool_FromLong (reload_p ? 1 : 0));
+  if (py_reload_p == nullptr
+      || evpy_add_attribute (event_obj.get (), "reload",
+			     py_reload_p.get ()) < 0)
+    return -1;
+
+  return evpy_emit_event (event_obj.get (), registry);
+}
+
+/* Listener for the executable_changed observable, this is called when the
+   current executable within PSPACE changes.  RELOAD_P is true if the
+   executable path stayed the same but the file changed on disk.  RELOAD_P
+   is false if the executable path was changed.  */
+
+static void
+gdbpy_executable_changed (struct program_space *pspace, bool reload_p)
+{
+  if (!gdb_python_initialized)
+    return;
+
+  gdbpy_enter enter_py;
+
+  if (!evregpy_no_listeners_p (gdb_py_events.executable_changed))
+    if (emit_executable_changed_event (gdb_py_events.executable_changed,
+				       pspace, reload_p) < 0)
+      gdbpy_print_stack ();
+}
+
 static int CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION
 gdbpy_initialize_pspace (void)
 {
+  gdb::observers::executable_changed.attach (gdbpy_executable_changed,
+					     "py-progspace");
+
   if (PyType_Ready (&pspace_object_type) < 0)
     return -1;
 
diff --git a/gdb/testsuite/gdb.python/py-exec-file.exp b/gdb/testsuite/gdb.python/py-exec-file.exp
index 14e5088..5ad3cd7 100644
--- a/gdb/testsuite/gdb.python/py-exec-file.exp
+++ b/gdb/testsuite/gdb.python/py-exec-file.exp
@@ -35,11 +35,59 @@ if {[build_executable "failed to prepare second executable" \
 set binfile1 [gdb_remote_download host $binfile1]
 set binfile2 [gdb_remote_download host $binfile2]
 
+# Setup a Python function to listen for the executable changed event.
+proc setup_exec_change_handler {} {
+    gdb_py_test_silent_cmd \
+	[multi_line \
+	     "python" \
+	     "def reset_state():" \
+	     "   global exec_changed_state" \
+	     "   exec_changed_state = \[0, None, None\]" \
+	     "end" ] \
+	"build reset_state function" 0
+
+    gdb_py_test_silent_cmd \
+	[multi_line \
+	     "python" \
+	     "def executable_changed(event):" \
+	     "   global exec_changed_state" \
+	     "   exec_changed_state\[0\] += 1" \
+	     "   exec_changed_state\[1\] = event.progspace.executable_filename" \
+	     "   exec_changed_state\[2\] = event.reload" \
+	     "end" ] \
+	"build executable_changed function" 0
+
+    gdb_test_no_output -nopass "python reset_state()"
+    gdb_test_no_output "python gdb.events.executable_changed.connect(executable_changed)"
+}
+
+# Check the global Python state that is updated when the
+# executable_changed event occurs, and then reset the global state.
+# FILENAME is a string, the name of the new executable file.  RELOAD
+# is a string, which should be 'True' or 'False', and represents if
+# the executable file was reloaded, or changed.
+proc check_exec_change { filename_re reload testname } {
+    if { $filename_re ne "None" } {
+	set filename_re "'$filename_re'"
+    }
+    if { $filename_re eq "None" && $reload eq "None" } {
+	set count 0
+    } else {
+	set count 1
+    }
+    gdb_test "python print(exec_changed_state)" \
+	"\\\[$count, $filename_re, $reload\\\]" \
+	$testname
+    gdb_test_no_output -nopass "python reset_state()"
+}
+
 # Check that the executable_filename is set correctly after using the
 # 'file' command.
 with_test_prefix "using 'file' command" {
     clean_restart
 
+    setup_exec_change_handler
+
     gdb_test "python print(gdb.current_progspace().executable_filename)" \
 	"None" \
 	"check executable_filename when no file is loaded"
@@ -51,6 +99,9 @@ with_test_prefix "using 'file' command" {
 	"[string_to_regexp $binfile1]" \
 	"check executable_filename when first executable is loaded"
 
+    check_exec_change [string_to_regexp $binfile1] False \
+	"check executable_changed state after first executable was loaded"
+
     gdb_test "file $binfile2" \
 	"Reading symbols from [string_to_regexp $binfile2]\\.\\.\\..*" \
 	"load second executable" \
@@ -59,42 +110,91 @@ with_test_prefix "using 'file' command" {
 	"[string_to_regexp $binfile2]" \
 	"check executable_filename when second executable is loaded"
 
+    check_exec_change [string_to_regexp $binfile2] False \
+	"check executable_changed state after second executable was loaded"
+
     gdb_unload
     gdb_test "python print(gdb.current_progspace().executable_filename)" \
 	"None" \
 	"check executable_filename after unloading file"
+
+    check_exec_change None False \
+	"check executable_changed state after unloading the executable"
 }
 
 # Check that the executable_filename is correctly set when we only set
 # the exec-file.
 with_test_prefix "using 'exec-file' command" {
     clean_restart
+
+    setup_exec_change_handler
+
     gdb_test_no_output "exec-file $binfile1" \
 	"load first executable"
     gdb_test "python print(gdb.current_progspace().executable_filename)" \
 	"[string_to_regexp $binfile1]" \
 	"check executable_filename when first executable is loaded"
 
+    check_exec_change [string_to_regexp $binfile1] False \
+	"check executable_changed state after first executable was loaded"
+
     gdb_test_no_output "exec-file $binfile2" \
 	"load second executable"
     gdb_test "python print(gdb.current_progspace().executable_filename)" \
 	"[string_to_regexp $binfile2]" \
 	"check executable_filename when second executable is loaded"
 
+    check_exec_change [string_to_regexp $binfile2] False \
+	"check executable_changed state after second executable was loaded"
+
     gdb_test "exec-file" "No executable file now\\."
     gdb_test "python print(gdb.current_progspace().executable_filename)" \
 	"None" \
 	"check executable_filename after unloading file"
+
+    check_exec_change None False \
+	"check executable_changed state after unloading the executable"
 }
 
 # Check that setting the symbol-file doesn't cause the
 # executable_filename to be set.
 with_test_prefix "using 'symbol-file' command" {
     clean_restart
+
+    setup_exec_change_handler
+
     gdb_test "symbol-file $binfile1" \
 	"Reading symbols from [string_to_regexp $binfile1]\\.\\.\\..*" \
 	"load first executable"
     gdb_test "python print(gdb.current_progspace().executable_filename)" \
 	"None" \
 	"check executable_filename after setting symbol-file"
+
+    check_exec_change None None \
+	"check executable_changed state after setting symbol-file"
+}
+
+# Check the executable_changed event when the executable changes on disk.
+with_test_prefix "exec changes on disk" {
+    clean_restart $binfile1
+
+    setup_exec_change_handler
+
+    runto_main
+
+    gdb_test_no_output "shell sleep 1" \
+	"ensure executable is at least 1 second old"
+
+    gdb_test "shell touch ${binfile1}" "" \
+	"update the executable on disk"
+
+    runto_main
+
+    # There is currently an issue where the executable_changed event
+    # will trigger twice during an inferior restart.  This should be
+    # fixed in the next commit, at which point this kfail can be
+    # removed.
+    setup_kfail "????" *-*-*
+    check_exec_change [string_to_regexp $binfile1] True \
+	"check executable_changed state after exec changed on disk"
 }