gdb/python: add some additional methods to gdb.PendingFrame

The gdb.Frame class has far more methods than gdb.PendingFrame.  Given
that a PendingFrame hasn't yet been claimed by an unwinder, there is a
limit to which methods we can add to it, but many of the methods that
the Frame class has, the PendingFrame class could also support.

In this commit I've added those methods to PendingFrame that I believe
are safe.

In terms of implementation: if I was starting from scratch then I
would implement many of these (or most of these) as attributes rather
than methods.  However, given both Frame and PendingFrame are just
different representation of a frame, I think there is value in keeping
the interface for the two classes the same.  For this reason
everything here is a method -- that's what the Frame class does.

The new methods I've added are:

  - gdb.PendingFrame.is_valid: Return True if the pending frame
    object is valid.

  - gdb.PendingFrame.name: Return the name for the frame's function,
    or None.

  - gdb.PendingFrame.pc: Return the $pc register value for this
    frame.

  - gdb.PendingFrame.language: Return a string containing the
    language for this frame, or None.

  - gdb.PendingFrame.find_sal: Return a gdb.Symtab_and_line object
    for the current location within the pending frame, or None.

  - gdb.PendingFrame.block: Return a gdb.Block for the current
    pending frame, or None.

  - gdb.PendingFrame.function: Return a gdb.Symbol for the current
    pending frame, or None.

In every case I've just copied the implementation over from gdb.Frame
and cleaned the code slightly e.g. NULL to nullptr.  Additionally each
function required a small update to reflect the PendingFrame type, but
that's pretty minor.

There are tests for all the new methods.

For more extensive testing, I added the following code to the file
gdb/python/lib/command/unwinders.py:

  from gdb.unwinder import Unwinder

  class TestUnwinder(Unwinder):
      def __init__(self):
          super().__init__("XXX_TestUnwinder_XXX")

      def __call__(self,pending_frame):
          lang = pending_frame.language()
          try:
              block = pending_frame.block()
              assert isinstance(block, gdb.Block)
          except RuntimeError as rte:
              assert str(rte) == "Cannot locate block for frame."
          function = pending_frame.function()
          arch = pending_frame.architecture()
          assert arch is None or isinstance(arch, gdb.Architecture)
          name = pending_frame.name()
          assert name is None or isinstance(name, str)
          valid = pending_frame.is_valid()
          pc = pending_frame.pc()
          sal = pending_frame.find_sal()
          assert sal is None or isinstance(sal, gdb.Symtab_and_line)
          return None

  gdb.unwinder.register_unwinder(None, TestUnwinder())

This registers a global unwinder that calls each of the new
PendingFrame methods and checks the result is of an acceptable type.
The unwinder never claims any frames though, so shouldn't change how
GDB actually behaves.

I then ran the testsuite.  There was only a single regression, a test
that uses 'disable unwinder' and expects a single unwinder to be
disabled -- the extra unwinder is now disabled too, which changes the
test output.  So I'm reasonably confident that the new methods are not
going to crash GDB.

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

5 files changed, 417 insertions, 1 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index a3f7e1c..d5316ff 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -120,6 +120,26 @@ show always-read-ctf
      without the particular unwinder, depending on how 'enabled' was
      changed.
 
+  ** New methods added to the gdb.PendingFrame class.  These methods
+     have the same behaviour as the corresponding methods on
+     gdb.Frame.  The new methods are:
+
+     - gdb.PendingFrame.name: Return the name for the frame's
+       function, or None.
+     - gdb.PendingFrame.is_valid: Return True if the pending frame
+       object is valid.
+     - gdb.PendingFrame.pc: Return the $pc register value for this
+       frame.
+     - gdb.PendingFrame.language: Return a string containing the
+       language for this frame, or None.
+     - gdb.PendingFrame.find_sal: Return a gdb.Symtab_and_line
+       object for the current location within the pending frame, or
+       None.
+     - gdb.PendingFrame.block: Return a gdb.Block for the current
+       pending frame, or None.
+     - gdb.PendingFrame.function: Return a gdb.Symbol for the
+       current pending frame, or None.
+
 *** 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 8dcb3da..80697f9 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -2830,6 +2830,46 @@ Return an integer, the stack frame level for this frame.
 @xref{Frames, ,Stack Frames}.
 @end defun
 
+@defun PendingFrame.name ()
+Returns the function name of this pending frame, or @code{None} if it
+can't be obtained.
+@end defun
+
+@defun PendingFrame.is_valid ()
+Returns true if the @code{gdb.PendingFrame} object is valid, false if
+not.  A pending frame object becomes invalid when the call to the
+unwinder, for which the pending frame was created, returns.
+
+All @code{gdb.PendingFrame} methods, except this one, will raise an
+exception if the pending frame object is invalid at the time the
+method is called.
+@end defun
+
+@defun PendingFrame.pc ()
+Returns the pending frame's resume address.
+@end defun
+
+@defun PendingFrame.block ()
+Return the pending frame's code block (@pxref{Blocks In Python}).  If
+the frame does not have a block -- for example, if there is no
+debugging information for the code in question -- then this will raise
+a @code{RuntimeError} exception.
+@end defun
+
+@defun PendingFrame.function ()
+Return the symbol for the function corresponding to this pending frame.
+@xref{Symbols In Python}.
+@end defun
+
+@defun PendingFrame.find_sal ()
+Return the pending frame's symtab and line object (@pxref{Symbol
+Tables In Python}).
+@end defun
+
+@defun PendingFrame.language ()
+Return the language of this frame, as a string, or None.
+@end defun
+
 @subheading Unwinder Output: UnwindInfo
 
 Use @code{PendingFrame.create_unwind_info} method described above to
diff --git a/gdb/python/py-unwind.c b/gdb/python/py-unwind.c
index 12b1461..5ed3ff3 100644
--- a/gdb/python/py-unwind.c
+++ b/gdb/python/py-unwind.c
@@ -28,6 +28,10 @@
 #include "regcache.h"
 #include "valprint.h"
 #include "user-regs.h"
+#include "stack.h"
+#include "charset.h"
+#include "block.h"
+
 
 /* Debugging of Python unwinders.  */
 
@@ -412,6 +416,200 @@ pending_framepy_read_register (PyObject *self, PyObject *args)
   return result;
 }
 
+/* Implement PendingFrame.is_valid().  Return True if this pending frame
+   object is still valid.  */
+
+static PyObject *
+pending_framepy_is_valid (PyObject *self, PyObject *args)
+{
+  pending_frame_object *pending_frame = (pending_frame_object *) self;
+
+  if (pending_frame->frame_info == nullptr)
+    Py_RETURN_FALSE;
+
+  Py_RETURN_TRUE;
+}
+
+/* Implement PendingFrame.name().  Return a string that is the name of the
+   function for this frame, or None if the name can't be found.  */
+
+static PyObject *
+pending_framepy_name (PyObject *self, PyObject *args)
+{
+  pending_frame_object *pending_frame = (pending_frame_object *) self;
+
+  PENDING_FRAMEPY_REQUIRE_VALID (pending_frame);
+
+  gdb::unique_xmalloc_ptr<char> name;
+
+  try
+    {
+      enum language lang;
+      frame_info_ptr frame = pending_frame->frame_info;
+
+      name = find_frame_funname (frame, &lang, nullptr);
+    }
+  catch (const gdb_exception &except)
+    {
+      GDB_PY_HANDLE_EXCEPTION (except);
+    }
+
+  if (name != nullptr)
+    return PyUnicode_Decode (name.get (), strlen (name.get ()),
+			     host_charset (), nullptr);
+
+  Py_RETURN_NONE;
+}
+
+/* Implement gdb.PendingFrame.pc().  Returns an integer containing the
+   frame's current $pc value.  */
+
+static PyObject *
+pending_framepy_pc (PyObject *self, PyObject *args)
+{
+  pending_frame_object *pending_frame = (pending_frame_object *) self;
+
+  PENDING_FRAMEPY_REQUIRE_VALID (pending_frame);
+
+  CORE_ADDR pc = 0;
+
+  try
+    {
+      pc = get_frame_pc (pending_frame->frame_info);
+    }
+  catch (const gdb_exception &except)
+    {
+      GDB_PY_HANDLE_EXCEPTION (except);
+    }
+
+  return gdb_py_object_from_ulongest (pc).release ();
+}
+
+/* Implement gdb.PendingFrame.language().  Return the name of the language
+   for this frame.  */
+
+static PyObject *
+pending_framepy_language (PyObject *self, PyObject *args)
+{
+  pending_frame_object *pending_frame = (pending_frame_object *) self;
+
+  PENDING_FRAMEPY_REQUIRE_VALID (pending_frame);
+
+  try
+    {
+      frame_info_ptr fi = pending_frame->frame_info;
+
+      enum language lang = get_frame_language (fi);
+      const language_defn *lang_def = language_def (lang);
+
+      return host_string_to_python_string (lang_def->name ()).release ();
+    }
+  catch (const gdb_exception &except)
+    {
+      GDB_PY_HANDLE_EXCEPTION (except);
+    }
+
+  Py_RETURN_NONE;
+}
+
+/* Implement PendingFrame.find_sal().  Return the PendingFrame's symtab and
+   line.  */
+
+static PyObject *
+pending_framepy_find_sal (PyObject *self, PyObject *args)
+{
+  pending_frame_object *pending_frame = (pending_frame_object *) self;
+
+  PENDING_FRAMEPY_REQUIRE_VALID (pending_frame);
+
+  PyObject *sal_obj = nullptr;
+
+  try
+    {
+      frame_info_ptr frame = pending_frame->frame_info;
+
+      symtab_and_line sal = find_frame_sal (frame);
+      sal_obj = symtab_and_line_to_sal_object (sal);
+    }
+  catch (const gdb_exception &except)
+    {
+      GDB_PY_HANDLE_EXCEPTION (except);
+    }
+
+  return sal_obj;
+}
+
+/* Implement PendingFrame.block().  Return a gdb.Block for the pending
+   frame's code, or raise  RuntimeError if the block can't be found.  */
+
+static PyObject *
+pending_framepy_block (PyObject *self, PyObject *args)
+{
+  pending_frame_object *pending_frame = (pending_frame_object *) self;
+
+  PENDING_FRAMEPY_REQUIRE_VALID (pending_frame);
+
+  frame_info_ptr frame = pending_frame->frame_info;
+  const struct block *block = nullptr, *fn_block;
+
+  try
+    {
+      block = get_frame_block (frame, nullptr);
+    }
+  catch (const gdb_exception &except)
+    {
+      GDB_PY_HANDLE_EXCEPTION (except);
+    }
+
+  for (fn_block = block;
+       fn_block != nullptr && fn_block->function () == nullptr;
+       fn_block = fn_block->superblock ())
+    ;
+
+  if (block == nullptr
+      || fn_block == nullptr
+      || fn_block->function () == nullptr)
+    {
+      PyErr_SetString (PyExc_RuntimeError,
+		       _("Cannot locate block for frame."));
+      return nullptr;
+    }
+
+  return block_to_block_object (block, fn_block->function ()->objfile ());
+}
+
+/* Implement gdb.PendingFrame.function().  Return a gdb.Symbol
+   representing the function of this frame, or None if no suitable symbol
+   can be found.  */
+
+static PyObject *
+pending_framepy_function (PyObject *self, PyObject *args)
+{
+  pending_frame_object *pending_frame = (pending_frame_object *) self;
+
+  PENDING_FRAMEPY_REQUIRE_VALID (pending_frame);
+
+  struct symbol *sym = nullptr;
+
+  try
+    {
+      enum language funlang;
+      frame_info_ptr frame = pending_frame->frame_info;
+
+      gdb::unique_xmalloc_ptr<char> funname
+	= find_frame_funname (frame, &funlang, &sym);
+    }
+  catch (const gdb_exception &except)
+    {
+      GDB_PY_HANDLE_EXCEPTION (except);
+    }
+
+  if (sym != nullptr)
+    return symbol_to_symbol_object (sym);
+
+  Py_RETURN_NONE;
+}
+
 /* Implementation of
    PendingFrame.create_unwind_info (self, frameId) -> UnwindInfo.  */
 
@@ -737,6 +935,29 @@ static PyMethodDef pending_frame_object_methods[] =
     pending_framepy_architecture, METH_NOARGS,
     "architecture () -> gdb.Architecture\n"
     "The architecture for this PendingFrame." },
+  { "name",
+    pending_framepy_name, METH_NOARGS,
+    "name() -> String.\n\
+Return the function name of the frame, or None if it can't be determined." },
+  { "is_valid",
+    pending_framepy_is_valid, METH_NOARGS,
+    "is_valid () -> Boolean.\n\
+Return true if this PendingFrame is valid, false if not." },
+  { "pc",
+    pending_framepy_pc, METH_NOARGS,
+    "pc () -> Long.\n\
+Return the frame's resume address." },
+  { "language", pending_framepy_language, METH_NOARGS,
+    "The language of this frame." },
+  { "find_sal", pending_framepy_find_sal, METH_NOARGS,
+    "find_sal () -> gdb.Symtab_and_line.\n\
+Return the frame's symtab and line." },
+  { "block", pending_framepy_block, METH_NOARGS,
+    "block () -> gdb.Block.\n\
+Return the frame's code block." },
+  { "function", pending_framepy_function, METH_NOARGS,
+    "function () -> gdb.Symbol.\n\
+Returns the symbol for the function corresponding to this frame." },
   { "level", pending_framepy_level, METH_NOARGS,
     "The stack level of this frame." },
   {NULL}  /* Sentinel */
diff --git a/gdb/testsuite/gdb.python/py-unwind.exp b/gdb/testsuite/gdb.python/py-unwind.exp
index 3e214ee..f670da5 100644
--- a/gdb/testsuite/gdb.python/py-unwind.exp
+++ b/gdb/testsuite/gdb.python/py-unwind.exp
@@ -149,15 +149,46 @@ gdb_test_no_output "python obj = simple_unwinder(\"simple\")"
 gdb_test_no_output "python gdb.unwinder.register_unwinder(None, obj)"
 check_for_broken_backtrace "backtrace to capture a PendingFrame object"
 
+# Check the captured PendingFrame is not valid.
+gdb_test "python print(captured_pending_frame.is_valid())" "False"
+
 # Call methods on the captured gdb.PendingFrame and check we see the
 # expected error.
 gdb_test_no_output "python pf = captured_pending_frame"
 foreach cmd {"pf.read_register(\"pc\")" \
 		 "pf.create_unwind_info(None)" \
 		 "pf.architecture()" \
-		 "pf.level()"} {
+		 "pf.level()" \
+		 "pf.name()" \
+		 "pf.pc()" \
+		 "pf.language()" \
+		 "pf.find_sal()" \
+		 "pf.block()" \
+		 "pf.function()" } {
     gdb_test "python $cmd" \
 	[multi_line \
 	     "ValueError: gdb\\.PendingFrame is invalid\\." \
 	     "Error while executing Python code\\."]
 }
+
+# Turn on the useful unwinder so we have the full backtrace again, and
+# disable the simple unwinder -- because we can!
+gdb_test "enable unwinder global \"test unwinder\"" \
+    "1 unwinder enabled" \
+    "re-enable 'test unwinder' so we can check PendingFrame methods"
+gdb_test "disable unwinder global \"simple\"" \
+    "1 unwinder disabled"
+check_for_fixed_backtrace \
+    "check backtrace before testing PendingFrame methods"
+
+# Gather information about every frame.
+gdb_test_no_output "python capture_all_frame_information()"
+gdb_test_no_output "python gdb.newest_frame().select()"
+gdb_test_no_output "python pspace = gdb.selected_inferior().progspace"
+gdb_test_no_output "python obj = validating_unwinder()"
+gdb_test_no_output "python gdb.unwinder.register_unwinder(pspace, obj)"
+
+check_for_fixed_backtrace \
+    "check backtrace to validate all information"
+
+gdb_test_no_output "python check_all_frame_information_matched()"
diff --git a/gdb/testsuite/gdb.python/py-unwind.py b/gdb/testsuite/gdb.python/py-unwind.py
index b30e843..8e3c1f3 100644
--- a/gdb/testsuite/gdb.python/py-unwind.py
+++ b/gdb/testsuite/gdb.python/py-unwind.py
@@ -144,9 +144,113 @@ class simple_unwinder(Unwinder):
     def __call__(self, pending_frame):
         global captured_pending_frame
 
+        assert pending_frame.is_valid()
+
         if captured_pending_frame is None:
             captured_pending_frame = pending_frame
         return None
 
 
+# Return a dictionary of information about FRAME.
+def capture_frame_information(frame):
+    name = frame.name()
+    level = frame.level()
+    language = frame.language()
+    function = frame.function()
+    architecture = frame.architecture()
+    pc = frame.pc()
+    sal = frame.find_sal()
+    try:
+        block = frame.block()
+        assert isinstance(block, gdb.Block)
+    except RuntimeError as rte:
+        assert str(rte) == "Cannot locate block for frame."
+        block = "RuntimeError: " + str(rte)
+
+    return {
+        "name": name,
+        "level": level,
+        "language": language,
+        "function": function,
+        "architecture": architecture,
+        "pc": pc,
+        "sal": sal,
+        "block": block,
+    }
+
+
+# List of information about each frame.  The index into this list is
+# the frame level.  This is populated by
+# capture_all_frame_information.
+all_frame_information = []
+
+# Fill in the global ALL_FRAME_INFORMATION list.
+def capture_all_frame_information():
+    global all_frame_information
+
+    all_frame_information = []
+
+    gdb.newest_frame().select()
+    frame = gdb.selected_frame()
+    count = 0
+
+    while frame is not None:
+        frame.select()
+        info = capture_frame_information(frame)
+        level = info["level"]
+        info["matched"] = False
+
+        while len(all_frame_information) <= level:
+            all_frame_information.append(None)
+
+        assert all_frame_information[level] is None
+        all_frame_information[level] = info
+
+        if frame.name == "main" or count > 10:
+            break
+
+        count += 1
+        frame = frame.older()
+
+
+# Assert that every entry in the global ALL_FRAME_INFORMATION list was
+# matched by the validating_unwinder.
+def check_all_frame_information_matched():
+    global all_frame_information
+    for entry in all_frame_information:
+        assert entry["matched"]
+
+
+# An unwinder that doesn't match any frames.  What it does do is
+# lookup information from the PendingFrame object and compare it
+# against information stored in the global ALL_FRAME_INFORMATION list.
+class validating_unwinder(Unwinder):
+    def __init__(self):
+        super().__init__("validating_unwinder")
+
+    def __call__(self, pending_frame):
+        info = capture_frame_information(pending_frame)
+        level = info["level"]
+
+        global all_frame_information
+        old_info = all_frame_information[level]
+
+        assert old_info is not None
+        assert not old_info["matched"]
+
+        for key, value in info.items():
+            assert key in old_info, f"{key} not in old_info"
+            assert type(value) == type(old_info[key])
+            if isinstance(value, gdb.Block):
+                assert value.start == old_info[key].start
+                assert value.end == old_info[key].end
+                assert value.is_static == old_info[key].is_static
+                assert value.is_global == old_info[key].is_global
+            else:
+                assert str(value) == str(old_info[key])
+
+        old_info["matched"] = True
+        return None
+
+
 print("Python script imported")