gdb/python: Add BreakpointLocation type

PR python/18385

v7:
This version addresses the issues pointed out by Tom.

Added nullchecks for Python object creations.

Changed from using PyLong_FromLong to the gdb_py-versions.

Re-factored some code to make it look more cohesive.

Also added the more safe Python reference count decrement PY_XDECREF,
even though the BreakpointLocation type is never instantiated by the
user (explicitly documented in the docs) decrementing < 0 is made
impossible with the safe call.

Tom pointed out that using the policy class explicitly to decrement a
reference counted object was not the way to go, so this has instead been
wrapped in a ref_ptr that handles that for us in blocpy_dealloc.

Moved macro from py-internal to py-breakpoint.c.

Renamed section at the bottom of commit message "Patch Description".

v6:
This version addresses the points Pedro gave in review to this patch.

Added the attributes `function`, `fullname` and `thread_groups`
as per request by Pedro with the argument that it more resembles the
output of the MI-command "-break-list".  Added documentation for these attributes.

Cleaned up left overs from copy+paste in test suite, removed hard coding
of line numbers where possible.

Refactored some code to use more c++-y style range for loops
wrt to breakpoint locations.

Changed terminology, naming was very inconsistent. Used a variety of "parent",
"owner". Now "owner" is the only term used, and the field in the
gdb_breakpoint_location_object now also called "owner".

v5:

Changes in response to review by Tom Tromey:
- Replaced manual INCREF/DECREF calls with
  gdbpy_ref ptrs in places where possible.
- Fixed non-gdb style conforming formatting
- Get parent of bploc increases ref count of parent.
- moved bploc Python definition to py-breakpoint.c

The INCREF of self in bppy_get_locations is due
to the individual locations holding a reference to
it's owner. This is decremented at de-alloc time.

The reason why this needs to be here is, if the user writes
for instance;

py loc = gdb.breakpoints()[X].locations[Y]

The breakpoint owner object is immediately going
out of scope (GC'd/dealloced), and the location
object requires it to be alive for as long as it is alive.

Thanks for your review, Tom!

v4:
Fixed remaining doc issues as per request
by Eli.

v3:
Rewritten commit message, shortened + reworded,
added tests.

Patch Description

Currently, the Python API lacks the ability to
query breakpoints for their installed locations,
and subsequently, can't query any information about them, or
enable/disable individual locations.

This patch solves this by adding Python type gdb.BreakpointLocation.
The type is never instantiated by the user of the Python API directly,
but is produced by the gdb.Breakpoint.locations attribute returning
a list of gdb.BreakpointLocation.

gdb.Breakpoint.locations:
The attribute for retrieving the currently installed breakpoint
locations for gdb.Breakpoint. Matches behavior of
the "info breakpoints" command in that it only
returns the last known or currently inserted breakpoint locations.

BreakpointLocation contains 7 attributes

6 read-only attributes:
owner: location owner's Python companion object
source: file path and line number tuple: (string, long) / None
address: installed address of the location
function: function name where location was set
fullname: fullname where location was set
thread_groups: thread groups (inferiors) where location was set.

1 writeable attribute:
enabled: get/set enable/disable this location (bool)

Access/calls to these, can all throw Python exceptions (documented in
the online documentation), and that's due to the nature
of how breakpoint locations can be invalidated
"behind the scenes", either by them being removed
from the original breakpoint or changed,
like for instance when a new symbol file is loaded, at
which point all breakpoint locations are re-created by GDB.
Therefore this patch has chosen to be non-intrusive:
it's up to the Python user to re-request the locations if
they become invalid.

Also there's event handlers that handle new object files etc, if a Python
user is storing breakpoint locations in some larger state they've
built up, refreshing the locations is easy and it only comes
with runtime overhead when the Python user wants to use them.

gdb.BreakpointLocation Python type
struct "gdbpy_breakpoint_location_object" is found in python-internal.h

Its definition, layout, methods and functions
are found in the same file as gdb.Breakpoint (py-breakpoint.c)

1 change was also made to breakpoint.h/c to make it possible
to enable and disable a bp_location* specifically,
without having its LOC_NUM, as this number
also can change arbitrarily behind the scenes.

Updated docs & news file as per request.

Testsuite: tests the .source attribute and the disabling of
individual locations.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=18385


Change-Id: I302c1c50a557ad59d5d18c88ca19014731d736b0

1 files changed, 316 insertions, 0 deletions

diff --git a/gdb/python/py-breakpoint.c b/gdb/python/py-breakpoint.c
index 2b9f6f3..48ec86c 100644
--- a/gdb/python/py-breakpoint.c
+++ b/gdb/python/py-breakpoint.c
@@ -34,6 +34,41 @@
 #include "py-event.h"
 #include "linespec.h"
 
+extern PyTypeObject breakpoint_location_object_type
+    CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF ("breakpoint_location_object");
+
+struct gdbpy_breakpoint_location_object
+{
+  PyObject_HEAD
+
+  /* An owning reference to the gdb breakpoint location object.  */
+  bp_location *bp_loc;
+
+  /* An owning reference to the location's breakpoint owner.  */
+  gdbpy_breakpoint_object *owner;
+};
+
+/* Require that BREAKPOINT and LOCATION->OWNER are the same; throw a Python
+   exception if they are not.  */
+#define BPLOCPY_REQUIRE_VALID(Breakpoint, Location)                         \
+    do {                                                                    \
+      if ((Breakpoint)->bp != (Location)->bp_loc->owner)                    \
+	return PyErr_Format (PyExc_RuntimeError,                            \
+			     _("Breakpoint location is invalid."));	    \
+    } while (0)
+
+/* Require that BREAKPOINT and LOCATION->OWNER are the same; throw a Python
+   exception if they are not.  This macro is for use in setter functions.  */
+#define BPLOCPY_SET_REQUIRE_VALID(Breakpoint, Location)                     \
+    do {                                                                    \
+      if ((Breakpoint)->bp != (Location)->bp_loc->owner)                    \
+	{                                                                   \
+	  PyErr_Format (PyExc_RuntimeError,                                 \
+			_("Breakpoint location is invalid."));		    \
+	  return -1;                                                        \
+	}                                                                   \
+    } while (0)
+
 /* Debugging of Python breakpoints.  */
 
 static bool pybp_debug;
@@ -692,6 +727,38 @@ bppy_get_ignore_count (PyObject *self, void *closure)
   return gdb_py_object_from_longest (self_bp->bp->ignore_count).release ();
 }
 
+/* Python function to get the breakpoint locations of an owner breakpoint.  */
+
+static PyObject *
+bppy_get_locations (PyObject *self, void *closure)
+{
+  using py_bploc_t = gdbpy_breakpoint_location_object;
+  auto *self_bp = (gdbpy_breakpoint_object *) self;
+  BPPY_REQUIRE_VALID (self_bp);
+
+  gdbpy_ref<> list (PyList_New (0));
+  if (list == nullptr)
+    return nullptr;
+
+  for (bp_location *loc : self_bp->bp->locations ())
+    {
+      gdbpy_ref<py_bploc_t> py_bploc
+	(PyObject_New (py_bploc_t, &breakpoint_location_object_type));
+      if (py_bploc == nullptr)
+	return nullptr;
+
+      bp_location_ref_ptr ref = bp_location_ref_ptr::new_reference (loc);
+      /* The location takes a reference to the owner breakpoint.
+	 Decrements when they are de-allocated in bplocpy_dealloc */
+      Py_INCREF (self);
+      py_bploc->owner = self_bp;
+      py_bploc->bp_loc = ref.release ();
+      if (PyList_Append (list.get (), (PyObject *) py_bploc.get ()) != 0)
+	return nullptr;
+    }
+  return list.release ();
+}
+
 /* Internal function to validate the Python parameters/keywords
    provided to bppy_init.  */
 
@@ -1185,6 +1252,21 @@ gdbpy_initialize_breakpoints (void)
   return 0;
 }
 
+/* Initialize the Python BreakpointLocation code.  */
+
+int
+gdbpy_initialize_breakpoint_locations ()
+{
+  if (PyType_Ready (&breakpoint_location_object_type) < 0)
+    return -1;
+
+  if (gdb_pymodule_addobject (gdb_module, "BreakpointLocation",
+			      (PyObject *) &breakpoint_location_object_type)
+      < 0)
+    return -1;
+  return 0;
+}
+
 
 
 /* Helper function that overrides this Python object's
@@ -1267,6 +1349,8 @@ or None if no condition set."},
     "Whether this breakpoint is a temporary breakpoint."},
   { "pending", bppy_get_pending, NULL,
     "Whether this breakpoint is a pending breakpoint."},
+  { "locations", bppy_get_locations, NULL,
+    "Get locations where this breakpoint was set"},
   { NULL }  /* Sentinel.  */
 };
 
@@ -1333,3 +1417,235 @@ _initialize_py_breakpoint ()
 	show_pybp_debug,
 	&setdebuglist, &showdebuglist);
 }
+
+/* Python function to set the enabled state of a breakpoint location.  */
+
+static int
+bplocpy_set_enabled (PyObject *py_self, PyObject *newvalue, void *closure)
+{
+  auto *self = (gdbpy_breakpoint_location_object *) py_self;
+  BPPY_SET_REQUIRE_VALID (self->owner);
+  BPLOCPY_SET_REQUIRE_VALID (self->owner, self);
+
+  if (newvalue == nullptr)
+    {
+      PyErr_SetString (PyExc_TypeError,
+		       _("Cannot delete 'enabled' attribute."));
+      return -1;
+    }
+  else if (!PyBool_Check (newvalue))
+    {
+      PyErr_SetString (PyExc_TypeError,
+		       _("The value of 'enabled' must be a boolean."));
+      return -1;
+    }
+
+  int cmp = PyObject_IsTrue (newvalue);
+  if (cmp < 0)
+    return -1;
+
+  try
+    {
+      enable_disable_bp_location (self->bp_loc, cmp == 1);
+    }
+  catch (const gdb_exception &except)
+    {
+      GDB_PY_SET_HANDLE_EXCEPTION (except);
+    }
+  return 0;
+}
+
+/* Python function to test whether or not the breakpoint location is enabled.  */
+
+static PyObject *
+bplocpy_get_enabled (PyObject *py_self, void *closure)
+{
+  auto *self = (gdbpy_breakpoint_location_object *) py_self;
+  BPPY_REQUIRE_VALID (self->owner);
+  BPLOCPY_REQUIRE_VALID (self->owner, self);
+
+  if (self->bp_loc->enabled)
+    Py_RETURN_TRUE;
+  else
+    Py_RETURN_FALSE;
+}
+
+/* Python function to get address of breakpoint location.  */
+
+static PyObject *
+bplocpy_get_address (PyObject *py_self, void *closure)
+{
+  auto *self = (gdbpy_breakpoint_location_object *) py_self;
+  BPPY_REQUIRE_VALID (self->owner);
+  BPLOCPY_REQUIRE_VALID (self->owner, self);
+  return gdb_py_object_from_ulongest (self->bp_loc->address).release ();
+}
+
+/* Python function to get owner of breakpoint location, which
+   is of type gdb.Breakpoint.  */
+
+static PyObject *
+bplocpy_get_owner (PyObject *py_self, void *closure)
+{
+  auto *self = (gdbpy_breakpoint_location_object *) py_self;
+  BPPY_REQUIRE_VALID (self->owner);
+  BPLOCPY_REQUIRE_VALID (self->owner, self);
+  Py_INCREF (self->owner);
+  return (PyObject *) self->owner;
+}
+
+/* Python function to get the source file name path and line number
+   where this breakpoint location was set.   */
+
+static PyObject *
+bplocpy_get_source_location (PyObject *py_self, void *closure)
+{
+  auto *self = (gdbpy_breakpoint_location_object *) py_self;
+  BPPY_REQUIRE_VALID (self->owner);
+  BPLOCPY_REQUIRE_VALID (self->owner, self);
+  if (self->bp_loc->symtab)
+    {
+      gdbpy_ref<> tup (PyTuple_New (2));
+      if (tup == nullptr)
+	return nullptr;
+      /* symtab->filename is never NULL. */
+      gdbpy_ref<> filename
+	= host_string_to_python_string (self->bp_loc->symtab->filename);
+      if (filename == nullptr)
+	return nullptr;
+      auto line = gdb_py_object_from_ulongest (self->bp_loc->line_number);
+      if (line == nullptr)
+	return nullptr;
+      if (PyTuple_SetItem (tup.get (), 0, filename.release ()) == -1
+	  || PyTuple_SetItem (tup.get (), 1, line.release ()) == -1)
+	return nullptr;
+      return tup.release ();
+    }
+  else
+    Py_RETURN_NONE;
+}
+
+/* Python function to get the function name of where this location was set.  */
+
+static PyObject *
+bplocpy_get_function (PyObject *py_self, void *closure)
+{
+  auto *self = (gdbpy_breakpoint_location_object *) py_self;
+  BPPY_REQUIRE_VALID (self->owner);
+  BPLOCPY_REQUIRE_VALID (self->owner, self);
+  const auto fn_name = self->bp_loc->function_name.get ();
+  if (fn_name != nullptr)
+    return host_string_to_python_string (fn_name).release ();
+  Py_RETURN_NONE;
+}
+
+static PyObject *
+bplocpy_get_thread_groups (PyObject *py_self, void *closure)
+{
+  auto *self = (gdbpy_breakpoint_location_object *) py_self;
+  BPPY_REQUIRE_VALID (self->owner);
+  BPLOCPY_REQUIRE_VALID (self->owner, self);
+  gdbpy_ref<> list (PyList_New (0));
+  if (list == nullptr)
+    return nullptr;
+  for (inferior *inf : all_inferiors ())
+    {
+      if (inf->pspace == self->bp_loc->pspace)
+	{
+	  gdbpy_ref<> num = gdb_py_object_from_ulongest (inf->num);
+	  if (num == nullptr)
+	    return nullptr;
+	  if (PyList_Append (list.get (), num.release ()) != 0)
+	    return nullptr;
+	}
+    }
+  return list.release ();
+}
+
+static PyObject *
+bplocpy_get_fullname (PyObject *py_self, void *closure)
+{
+  auto *self = (gdbpy_breakpoint_location_object *) py_self;
+  BPPY_REQUIRE_VALID (self->owner);
+  BPLOCPY_REQUIRE_VALID (self->owner, self);
+  const auto symtab = self->bp_loc->symtab;
+  if (symtab != nullptr && symtab->fullname != nullptr)
+    {
+      gdbpy_ref<> fullname
+	= host_string_to_python_string (symtab->fullname);
+      return fullname.release ();
+    }
+  Py_RETURN_NONE;
+}
+
+/* De-allocation function to be called for the Python object.  */
+
+static void
+bplocpy_dealloc (PyObject *py_self)
+{
+  auto *self = (gdbpy_breakpoint_location_object *) py_self;
+  bp_location_ref_ptr decrementing_ref {self->bp_loc};
+  Py_XDECREF (self->owner);
+  Py_TYPE (py_self)->tp_free (py_self);
+}
+
+/* Attribute get/set Python definitions. */
+
+static gdb_PyGetSetDef bp_location_object_getset[] = {
+  { "enabled", bplocpy_get_enabled, bplocpy_set_enabled,
+    "Boolean telling whether the breakpoint is enabled.", NULL },
+  { "owner", bplocpy_get_owner, NULL,
+    "Get the breakpoint owner object", NULL },
+  { "address", bplocpy_get_address, NULL,
+    "Get address of where this location was set", NULL},
+  { "source", bplocpy_get_source_location, NULL,
+    "Get file and line number of where this location was set", NULL},
+  { "function", bplocpy_get_function, NULL,
+    "Get function of where this location was set", NULL },
+  { "fullname", bplocpy_get_fullname, NULL,
+    "Get fullname of where this location was set", NULL },
+  { "thread_groups", bplocpy_get_thread_groups, NULL,
+    "Get thread groups where this location is in", NULL },
+  { NULL }  /* Sentinel.  */
+};
+
+PyTypeObject breakpoint_location_object_type =
+{
+  PyVarObject_HEAD_INIT (NULL, 0)
+  "gdb.BreakpointLocation",		/*tp_name*/
+  sizeof (gdbpy_breakpoint_location_object), /*tp_basicsize*/
+  0,					/*tp_itemsize*/
+  bplocpy_dealloc,  			/*tp_dealloc*/
+  0,					/*tp_print*/
+  0,					/*tp_getattr*/
+  0,					/*tp_setattr*/
+  0,					/*tp_compare*/
+  0,					/*tp_repr*/
+  0,					/*tp_as_number*/
+  0,					/*tp_as_sequence*/
+  0,					/*tp_as_mapping*/
+  0,					/*tp_hash */
+  0,					/*tp_call*/
+  0,					/*tp_str*/
+  0,					/*tp_getattro*/
+  0,          				/*tp_setattro */
+  0,					/*tp_as_buffer*/
+  Py_TPFLAGS_DEFAULT,			/*tp_flags*/
+  "GDB breakpoint location object",	/* tp_doc */
+  0,					/* tp_traverse */
+  0,					/* tp_clear */
+  0,					/* tp_richcompare */
+  0,					/* tp_weaklistoffset */
+  0,					/* tp_iter */
+  0,					/* tp_iternext */
+  0,					/* tp_methods */
+  0,					/* tp_members */
+  bp_location_object_getset,		/* tp_getset */
+  0,					/* tp_base */
+  0,					/* tp_dict */
+  0,					/* tp_descr_get */
+  0,					/* tp_descr_set */
+  0,					/* tp_dictoffset */
+  0,					/* tp_init */
+  0,					/* tp_alloc */
+};