[PATCH] [gdb/python]: add the orginal_value field in RegisterChangedEvent

[guoshengyuan1 <guoshengyuan1@xiaomi.com>]

When the register_changed event is triggered, the user should be told
what the previous value was so they can make a decision, rather
than just being told what the modified value is.

Signed-off-by: guoshengyuan1 <guoshengyuan1@xiaomi.com>
---
 gdb/doc/python.texi                   |  3 +++
 gdb/observable.h                      |  4 +++-
 gdb/python/py-event.h                 |  2 +-
 gdb/python/py-inferior.c              |  6 ++++--
 gdb/python/py-infevents.c             | 19 ++++++++++++++++---
 gdb/testsuite/gdb.python/py-events.py |  1 +
 gdb/tui/tui-hooks.c                   |  4 +++-
 gdb/valops.c                          |  4 +++-
 8 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index 3763eee9d63..1d74910f400 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -3979,6 +3979,9 @@ A gdb.Frame object representing the frame in which the register was modified.
 @defvar RegisterChangedEvent.regnum
 Denotes which register was modified.
 @end defvar
+@defvar RegisterChangedEvent.original_value
+Denotes the value of the register before it is modified.
+@end defvar

 @item events.breakpoint_created
 This is emitted when a new breakpoint has been created.  The argument
diff --git a/gdb/observable.h b/gdb/observable.h
index 4d913010c56..f65d42a2b00 100644
--- a/gdb/observable.h
+++ b/gdb/observable.h
@@ -20,6 +20,7 @@
 #ifndef GDB_OBSERVABLE_H
 #define GDB_OBSERVABLE_H

+#include "gdbsupport/common-types.h"
 #include "gdbsupport/observable.h"
 #include "target/waitstatus.h"

@@ -222,7 +223,8 @@ 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<const frame_info_ptr &/* frame */, int /* regnum */>
+extern observable<const frame_info_ptr &/* frame */, int /* regnum */,
+                 LONGEST /* original_value */>
     register_changed;

 /* The user-selected inferior, thread and/or frame has changed.  The
diff --git a/gdb/python/py-event.h b/gdb/python/py-event.h
index 3938368c9ca..2b696e23ff8 100644
--- a/gdb/python/py-event.h
+++ b/gdb/python/py-event.h
@@ -56,7 +56,7 @@ enum inferior_call_kind
 extern int emit_inferior_call_event (inferior_call_kind kind,
                                     ptid_t thread, CORE_ADDR addr);
 extern int emit_register_changed_event (const frame_info_ptr &frame,
-                                       int regnum);
+                                       int regnum, LONGEST original_value);
 extern int emit_memory_changed_event (CORE_ADDR addr, ssize_t len);
 extern int evpy_emit_event (PyObject *event,
                            eventregistry_object *registry);
diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c
index 2aa11d3160d..91f4bd862e5 100644
--- a/gdb/python/py-inferior.c
+++ b/gdb/python/py-inferior.c
@@ -19,6 +19,7 @@

 #include "auto-load.h"
 #include "gdbcore.h"
+#include "gdbsupport/common-types.h"
 #include "gdbthread.h"
 #include "inferior.h"
 #include "objfiles.h"
@@ -158,11 +159,12 @@ python_on_memory_change (struct inferior *inferior, CORE_ADDR addr, ssize_t len,
    command). */

 static void
-python_on_register_change (const frame_info_ptr &frame, int regnum)
+python_on_register_change (const frame_info_ptr &frame, int regnum,
+                          LONGEST orginal_value)
 {
   gdbpy_enter enter_py (current_inferior ()->arch ());

-  if (emit_register_changed_event (frame, regnum) < 0)
+  if (emit_register_changed_event (frame, regnum, orginal_value) < 0)
     gdbpy_print_stack ();
 }

diff --git a/gdb/python/py-infevents.c b/gdb/python/py-infevents.c
index f74fb017edc..424abffcd1c 100644
--- a/gdb/python/py-infevents.c
+++ b/gdb/python/py-infevents.c
@@ -17,6 +17,7 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

+#include "gdbsupport/common-types.h"
 #include "py-event.h"

 /* Construct either a gdb.InferiorCallPreEvent or a
@@ -62,7 +63,8 @@ create_inferior_call_event_object (inferior_call_kind flag, ptid_t ptid,

 static gdbpy_ref<>
 create_register_changed_event_object (const frame_info_ptr &frame,
-                                     int regnum)
+                                     int regnum,
+                                     LONGEST original_value)
 {
   gdbpy_ref<> event = create_event_object (&register_changed_event_object_type);
   if (event == NULL)
@@ -82,6 +84,15 @@ create_register_changed_event_object (const frame_info_ptr &frame,
   if (evpy_add_attribute (event.get (), "regnum", regnum_obj.get ()) < 0)
     return NULL;

+  gdbpy_ref<> original_value_obj = gdb_py_object_from_longest (original_value);
+  if (original_value_obj == NULL)
+    return NULL;
+
+  auto original_value_status = evpy_add_attribute
+    (event.get (), "original_value", original_value_obj.get ());
+  if (original_value_status < 0)
+    return NULL;
+
   return event;
 }

@@ -150,12 +161,14 @@ emit_memory_changed_event (CORE_ADDR addr, ssize_t len)
    will create a new Python register changed event object. */

 int
-emit_register_changed_event (const frame_info_ptr &frame, int regnum)
+emit_register_changed_event (const frame_info_ptr &frame, int regnum,
+                            LONGEST original_value)
 {
   if (evregpy_no_listeners_p (gdb_py_events.register_changed))
     return 0;

-  gdbpy_ref<> event = create_register_changed_event_object (frame, regnum);
+  gdbpy_ref<> event = create_register_changed_event_object
+    (frame, regnum, original_value);
   if (event != NULL)
     return evpy_emit_event (event.get (), gdb_py_events.register_changed);
   return -1;
diff --git a/gdb/testsuite/gdb.python/py-events.py b/gdb/testsuite/gdb.python/py-events.py
index 0573b16659b..663b9fb2119 100644
--- a/gdb/testsuite/gdb.python/py-events.py
+++ b/gdb/testsuite/gdb.python/py-events.py
@@ -90,6 +90,7 @@ def register_changed_handler(event):
     assert isinstance(event.frame, gdb.Frame)
     print("frame: %s" % (event.frame))
     print("num: %s" % (event.regnum))
+    print("num: %s" % (event.original_value))


 def memory_changed_handler(event):
diff --git a/gdb/tui/tui-hooks.c b/gdb/tui/tui-hooks.c
index 024fedd9955..e6bc56a26d4 100644
--- a/gdb/tui/tui-hooks.c
+++ b/gdb/tui/tui-hooks.c
@@ -17,6 +17,7 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

+#include "gdbsupport/common-types.h"
 #include "symtab.h"
 #include "inferior.h"
 #include "symfile.h"
@@ -47,7 +48,8 @@ tui_new_objfile_hook (struct objfile* objfile)
 /* Observer for the register_changed notification.  */

 static void
-tui_register_changed (const frame_info_ptr &frame, int regno)
+tui_register_changed (const frame_info_ptr &frame, int regno,
+                     LONGEST original_value)
 {
   frame_info_ptr fi;

diff --git a/gdb/valops.c b/gdb/valops.c
index fa87546770a..df8582336d2 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -1194,6 +1194,8 @@ value_assign (struct value *toval, struct value *fromval)
       {
        frame_info_ptr next_frame = frame_find_by_id (toval->next_frame_id ());
        int value_reg = toval->regnum ();
+       const auto original_value_reg = value_as_long
+         (get_frame_register_value(frame_find_by_id(old_frame), value_reg));

        if (next_frame == nullptr)
          error (_("Value being assigned to is no longer active."));
@@ -1255,7 +1257,7 @@ value_assign (struct value *toval, struct value *fromval)
          }

        gdb::observers::register_changed.notify
-         (get_prev_frame_always (next_frame), value_reg);
+         (get_prev_frame_always (next_frame), value_reg, original_value_reg);
        break;
       }

--
2.47.3

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