gdb/gdb-archer.patch

From a33be5ba95917ec49fc015387bfc9176fc78180c Mon Sep 17 00:00:00 2001
From: Fedora GDB patches <invalid@email.com>
Date: Fri, 27 Oct 2017 21:07:50 +0200
Subject: gdb-archer.patch

FileName: gdb-archer.patch

;; Python patches of: http://sourceware.org/gdb/wiki/ProjectArcher
;;=push

http://sourceware.org/gdb/wiki/ProjectArcher
http://sourceware.org/gdb/wiki/ArcherBranchManagement

GIT snapshot:
commit 718a1618b2f691a7f407213bb50f100ac59f91c3

tromey/python
---
 gdb/Makefile.in                             |   6 ++
 gdb/data-directory/Makefile.in              |   4 +
 gdb/doc/gdb.texinfo                         |  10 +++
 gdb/doc/python.texi                         |   2 -
 gdb/gdb-gdb.gdb.in                          |  10 +++
 gdb/main.c                                  |  93 ++++++++++++++++++-----
 gdb/python/lib/gdb/command/ignore_errors.py |  37 +++++++++
 gdb/python/lib/gdb/command/pahole.py        |  81 ++++++++++++++++++++
 gdb/python/lib/gdb/function/in_scope.py     |  47 ++++++++++++
 gdb/python/python-internal.h                |   3 +
 gdb/python/python.c                         | 113 ++++++++++++++++++++++++++++
 gdb/python/python.h                         |   2 +
 gdb/testsuite/gdb.python/py-frame.exp       |   2 +
 gdb/testsuite/gdb.python/py-value.exp       |  10 +++
 gdb/varobj.c                                |   8 ++
 gdb/varobj.h                                |   2 +
 16 files changed, 411 insertions(+), 19 deletions(-)
 create mode 100644 gdb/python/lib/gdb/command/ignore_errors.py
 create mode 100644 gdb/python/lib/gdb/command/pahole.py
 create mode 100644 gdb/python/lib/gdb/function/in_scope.py

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index edd0b239d4..0c3f89aa7e 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -2113,6 +2113,12 @@ stamp-h: $(srcdir)/config.in config.status
 	  CONFIG_LINKS= \
 	  $(SHELL) config.status
 
+.gdbinit: $(srcdir)/gdbinit.in config.status
+	CONFIG_FILES=".gdbinit:gdbinit.in" \
+	  CONFIG_COMMANDS= \
+	  CONFIG_HEADERS= \
+	  $(SHELL) config.status
+
 config.status: $(srcdir)/configure configure.tgt configure.host ../bfd/development.sh
 	$(SHELL) config.status --recheck
 
diff --git a/gdb/data-directory/Makefile.in b/gdb/data-directory/Makefile.in
index dadde8895a..19e436d725 100644
--- a/gdb/data-directory/Makefile.in
+++ b/gdb/data-directory/Makefile.in
@@ -80,6 +80,8 @@ PYTHON_FILE_LIST = \
 	gdb/unwinder.py \
 	gdb/xmethod.py \
 	gdb/command/__init__.py \
+	gdb/command/ignore_errors.py \
+	gdb/command/pahole.py \
 	gdb/command/explore.py \
 	gdb/command/backtrace.py \
 	gdb/command/frame_filters.py \
@@ -92,6 +94,8 @@ PYTHON_FILE_LIST = \
 	gdb/function/as_string.py \
 	gdb/function/caller_is.py \
 	gdb/function/strfns.py \
+	gdb/function/caller_is.py \
+	gdb/function/in_scope.py \
 	gdb/printer/__init__.py \
 	gdb/printer/bound_registers.py
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index a79c686f0b..d13d4dd945 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -1240,6 +1240,16 @@ for remote debugging.
 Run using @var{device} for your program's standard input and output.
 @c FIXME: kingdon thinks there is more to -tty.  Investigate.
 
+@item -P
+@cindex @code{-P}
+@itemx --python
+@cindex @code{--python}
+Change interpretation of command line so that the argument immediately
+following this switch is taken to be the name of a Python script file.
+This option stops option processing; subsequent options are passed to
+Python as @code{sys.argv}.  This option is only available if Python
+scripting support was enabled when @value{GDBN} was configured.
+
 @c resolve the situation of these eventually
 @item -tui
 @cindex @code{--tui}
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index 01243c7c7d..eb7bf3ca05 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -88,8 +88,6 @@ containing @code{end}.  For example:
 
 @smallexample
 (@value{GDBP}) python
-Type python script
-End with a line saying just "end".
 >print 23
 >end
 23
diff --git a/gdb/gdb-gdb.gdb.in b/gdb/gdb-gdb.gdb.in
index 05a38b2670..9801fdff67 100644
--- a/gdb/gdb-gdb.gdb.in
+++ b/gdb/gdb-gdb.gdb.in
@@ -1,5 +1,15 @@
 echo Setting up the environment for debugging gdb.\n
 
+# Set up the Python library and "require" command.
+python
+from os.path import abspath
+gdb.datadir = abspath ('@srcdir@/python/lib')
+gdb.pythonlibdir = gdb.datadir
+gdb.__path__ = [gdb.datadir + '/gdb']
+sys.path.insert(0, gdb.datadir)
+end
+source @srcdir@/python/lib/gdb/__init__.py
+
 if !$gdb_init_done
   set variable $gdb_init_done = 1
 
diff --git a/gdb/main.c b/gdb/main.c
index df1f12bd79..a530a632bf 100644
--- a/gdb/main.c
+++ b/gdb/main.c
@@ -33,6 +33,7 @@
 
 #include "interps.h"
 #include "main.h"
+#include "python/python.h"
 #include "source.h"
 #include "cli/cli-cmds.h"
 #include "objfiles.h"
@@ -478,7 +479,7 @@ exec_or_core_file_attach (const char *filename, int from_tty)
 }
 
 static void
-captured_main_1 (struct captured_main_args *context)
+captured_main_1 (struct captured_main_args *context, int &python_script)
 {
   int argc = context->argc;
   char **argv = context->argv;
@@ -695,10 +696,14 @@ captured_main_1 (struct captured_main_args *context)
       {"args", no_argument, &set_args, 1},
       {"l", required_argument, 0, 'l'},
       {"return-child-result", no_argument, &return_child_result, 1},
+#if HAVE_PYTHON
+      {"python", no_argument, 0, 'P'},
+      {"P", no_argument, 0, 'P'},
+#endif
       {0, no_argument, 0, 0}
     };
 
-    while (1)
+    while (!python_script)
       {
 	int option_index;
 
@@ -716,6 +721,9 @@ captured_main_1 (struct captured_main_args *context)
 	  case 0:
 	    /* Long option that just sets a flag.  */
 	    break;
+	  case 'P':
+	    python_script = 1;
+	    break;
 	  case OPT_SE:
 	    symarg = optarg;
 	    execarg = optarg;
@@ -888,7 +896,31 @@ captured_main_1 (struct captured_main_args *context)
 
   /* Now that gdb_init has created the initial inferior, we're in
      position to set args for that inferior.  */
-  if (set_args)
+  if (python_script)
+    {
+      /* The first argument is a python script to evaluate, and
+	 subsequent arguments are passed to the script for
+	 processing there.  */
+      if (optind >= argc)
+	{
+	  fprintf_unfiltered (gdb_stderr,
+			      _("%s: Python script file name required\n"),
+			      argv[0]);
+	  exit (1);
+	}
+
+      /* FIXME: should handle inferior I/O intelligently here.
+	 E.g., should be possible to run gdb in pipeline and have
+	 Python (and gdb) output go to stderr or file; and if a
+	 prompt is needed, open the tty.  */
+      quiet = 1;
+      /* FIXME: should read .gdbinit if, and only if, a prompt is
+	 requested by the script.  Though... maybe this is not
+	 ideal?  */
+      /* FIXME: likewise, reading in history.  */
+      inhibit_gdbinit = 1;
+    }
+  else if (set_args)
     {
       /* The remaining options are the command-line options for the
 	 inferior.  The first one is the sym/exec file, and the rest
@@ -1178,7 +1210,8 @@ captured_main_1 (struct captured_main_args *context)
 
   /* Read in the old history after all the command files have been
      read.  */
-  init_history ();
+  if (!python_script)
+    init_history ();
 
   if (batch_flag)
     {
@@ -1191,24 +1224,37 @@ static void
 captured_main (void *data)
 {
   struct captured_main_args *context = (struct captured_main_args *) data;
+  int python_script = 0;
 
-  captured_main_1 (context);
+  captured_main_1 (context, python_script);
 
-  /* NOTE: cagney/1999-11-07: There is probably no reason for not
-     moving this loop and the code found in captured_command_loop()
-     into the command_loop() proper.  The main thing holding back that
-     change - SET_TOP_LEVEL() - has been eliminated.  */
-  while (1)
+#if HAVE_PYTHON
+  if (python_script)
     {
-      TRY
-	{
-	  captured_command_loop ();
-	}
-      CATCH (ex, RETURN_MASK_ALL)
+      extern int pagination_enabled;
+      pagination_enabled = 0;
+      run_python_script (context->argc - optind, &context->argv[optind]);
+      return;
+    }
+  else
+#endif
+    {
+      /* NOTE: cagney/1999-11-07: There is probably no reason for not
+	 moving this loop and the code found in captured_command_loop()
+	 into the command_loop() proper.  The main thing holding back that
+	 change - SET_TOP_LEVEL() - has been eliminated. */
+      while (1)
 	{
-	  exception_print (gdb_stderr, ex);
+	  TRY
+	    {
+	      captured_command_loop ();
+	    }
+	  CATCH (ex, RETURN_MASK_ALL)
+	    {
+	      exception_print (gdb_stderr, ex);
+	    }
+	  END_CATCH
 	}
-      END_CATCH
     }
   /* No exit -- exit is through quit_command.  */
 }
@@ -1251,6 +1297,12 @@ print_gdb_help (struct ui_file *stream)
   fputs_unfiltered (_("\
 This is the GNU debugger.  Usage:\n\n\
     gdb [options] [executable-file [core-file or process-id]]\n\
+    gdb [options] --args executable-file [inferior-arguments ...]\n"), stream);
+#if HAVE_PYTHON
+  fputs_unfiltered (_("\
+    gdb [options] [--python|-P] script-file [script-arguments ...]\n"), stream);
+#endif
+  fputs_unfiltered (_("\n\
     gdb [options] --args executable-file [inferior-arguments ...]\n\n\
 "), stream);
   fputs_unfiltered (_("\
@@ -1296,6 +1348,13 @@ Output and user interface control:\n\n\
 #endif
   fputs_unfiltered (_("\
   --dbx              DBX compatibility mode.\n\
+"), stream);
+#if HAVE_PYTHON
+  fputs_unfiltered (_("\
+  --python, -P       Following argument is Python script file; remaining\n\
+                     arguments are passed to script.\n"), stream);
+#endif
+  fputs_unfiltered (_("\
   -q, --quiet, --silent\n\
                      Do not print version number on startup.\n\n\
 "), stream);
diff --git a/gdb/python/lib/gdb/command/ignore_errors.py b/gdb/python/lib/gdb/command/ignore_errors.py
new file mode 100644
index 0000000000..6fa48ff081
--- /dev/null
+++ b/gdb/python/lib/gdb/command/ignore_errors.py
@@ -0,0 +1,37 @@
+# Ignore errors in user commands.
+
+# Copyright (C) 2008 Free Software Foundation, Inc.
+
+# 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/>.
+
+import gdb
+
+class IgnoreErrorsCommand (gdb.Command):
+    """Execute a single command, ignoring all errors.
+Only one-line commands are supported.
+This is primarily useful in scripts."""
+
+    def __init__ (self):
+        super (IgnoreErrorsCommand, self).__init__ ("ignore-errors",
+                                                    gdb.COMMAND_OBSCURE,
+                                                    # FIXME...
+                                                    gdb.COMPLETE_COMMAND)
+
+    def invoke (self, arg, from_tty):
+        try:
+            gdb.execute (arg, from_tty)
+        except:
+            pass
+
+IgnoreErrorsCommand ()
diff --git a/gdb/python/lib/gdb/command/pahole.py b/gdb/python/lib/gdb/command/pahole.py
new file mode 100644
index 0000000000..e08eaf5ca8
--- /dev/null
+++ b/gdb/python/lib/gdb/command/pahole.py
@@ -0,0 +1,81 @@
+# pahole command for gdb
+
+# Copyright (C) 2008, 2009, 2012 Free Software Foundation, Inc.
+
+# 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/>.
+
+import gdb
+
+class Pahole (gdb.Command):
+    """Show the holes in a structure.
+This command takes a single argument, a type name.
+It prints the type and displays comments showing where holes are."""
+
+    def __init__ (self):
+        super (Pahole, self).__init__ ("pahole", gdb.COMMAND_NONE,
+                                       gdb.COMPLETE_SYMBOL)
+
+    def maybe_print_hole(self, bitpos, field_bitpos):
+        if bitpos != field_bitpos:
+            hole = field_bitpos - bitpos
+            print ('  /* XXX %d bit hole, try to pack */' % hole)
+
+    def pahole (self, type, level, name):
+        if name is None:
+            name = ''
+        tag = type.tag
+        if tag is None:
+            tag = ''
+        print ('%sstruct %s {' % (' ' * (2 * level), tag))
+        bitpos = 0
+        for field in type.fields ():
+            # Skip static fields.
+            if not hasattr (field, ('bitpos')):
+                continue
+
+            ftype = field.type.strip_typedefs()
+
+            self.maybe_print_hole(bitpos, field.bitpos)
+            bitpos = field.bitpos
+            if field.bitsize > 0:
+                fieldsize = field.bitsize
+            else:
+                # TARGET_CHAR_BIT here...
+                fieldsize = 8 * ftype.sizeof
+
+            # TARGET_CHAR_BIT
+            print (' /* %3d %3d */' % (int (bitpos / 8), int (fieldsize / 8)), end = "")
+            bitpos = bitpos + fieldsize
+
+            if ftype.code == gdb.TYPE_CODE_STRUCT:
+                self.pahole (ftype, level + 1, field.name)
+            else:
+                print (' ' * (2 + 2 * level), end = "")
+                print ('%s %s' % (str (ftype), field.name))
+
+        if level == 0:
+            self.maybe_print_hole(bitpos, 8 * type.sizeof)
+
+        print (' ' * (14 + 2 * level), end = "")
+        print ('} %s' % name)
+
+    def invoke (self, arg, from_tty):
+        type = gdb.lookup_type (arg)
+        type = type.strip_typedefs ()
+        if type.code != gdb.TYPE_CODE_STRUCT:
+            raise (TypeError, '%s is not a struct type' % arg)
+        print (' ' * 14, end = "")
+        self.pahole (type, 0, '')
+
+Pahole()
diff --git a/gdb/python/lib/gdb/function/in_scope.py b/gdb/python/lib/gdb/function/in_scope.py
new file mode 100644
index 0000000000..8742680614
--- /dev/null
+++ b/gdb/python/lib/gdb/function/in_scope.py
@@ -0,0 +1,47 @@
+# In-scope function.
+
+# Copyright (C) 2008 Free Software Foundation, Inc.
+
+# 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/>.
+
+import gdb
+
+class InScope (gdb.Function):
+    """Return True if all the given variables or macros are in scope.
+Takes one argument for each variable name to be checked."""
+
+    def __init__ (self):
+        super (InScope, self).__init__ ("in_scope")
+
+    def invoke (self, *vars):
+        if len (vars) == 0:
+            raise (TypeError, "in_scope takes at least one argument")
+
+        # gdb.Value isn't hashable so it can't be put in a map.
+        # Convert to string first.
+        wanted = set (map (lambda x: x.string (), vars))
+        found = set ()
+        block = gdb.selected_frame ().block ()
+        while block:
+            for sym in block:
+                if (sym.is_argument or sym.is_constant
+                      or sym.is_function or sym.is_variable):
+                    if sym.name in wanted:
+                        found.add (sym.name)
+
+            block = block.superblock
+
+        return wanted == found
+
+InScope ()
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index f099ae437f..468b0ebd92 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -651,6 +651,9 @@ class gdbpy_enter_varobj : public gdbpy_enter
 
 };
 
+struct cleanup *ensure_python_env (struct gdbarch *gdbarch,
+				   const struct language_defn *language);
+
 extern struct gdbarch *python_gdbarch;
 extern const struct language_defn *python_language;
 
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 0f71a4335e..03f6c55d40 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -95,6 +95,8 @@ const struct extension_language_defn extension_language_python =
 #include "linespec.h"
 #include "source.h"
 #include "version.h"
+#include "inferior.h"
+#include "gdbthread.h"
 #include "target.h"
 #include "gdbthread.h"
 #include "interps.h"
@@ -242,6 +244,29 @@ gdbpy_enter::~gdbpy_enter ()
   restore_active_ext_lang (m_previous_active);
 }
 
+static void
+restore_python_env (void *p)
+{
+  gdbpy_enter *env = (gdbpy_enter *) p;
+
+  delete env;
+}
+
+/* Called before entering the Python interpreter to install the
+   current language and architecture to be used for Python values.
+   Also set the active extension language for GDB so that SIGINT's
+   are directed our way, and if necessary install the right SIGINT
+   handler.  */
+
+struct cleanup *
+ensure_python_env (struct gdbarch *gdbarch,
+                   const struct language_defn *language)
+{
+  gdbpy_enter *env = new gdbpy_enter (gdbarch, language);
+
+  return make_cleanup (restore_python_env, env);
+}
+
 /* Set the quit flag.  */
 
 static void
@@ -1356,6 +1381,92 @@ gdbpy_print_stack (void)
 
 /* Return the current Progspace.
    There always is one.  */
+/* True if 'gdb -P' was used, false otherwise.  */
+static int running_python_script;
+
+/* True if we are currently in a call to 'gdb.cli', false otherwise.  */
+static int in_cli;
+
+/* Enter the command loop.  */
+
+static PyObject *
+gdbpy_cli (PyObject *unused1, PyObject *unused2)
+{
+  if (! running_python_script || in_cli)
+    return PyErr_Format (PyExc_RuntimeError, "cannot invoke CLI recursively");
+  
+  if (current_uiout->is_mi_like_p ())
+    return PyErr_Format (PyExc_RuntimeError, _("Cannot invoke CLI from MI."));
+
+  in_cli = 1;
+  /* See captured_command_loop.  */
+
+  /* Give the interpreter a chance to print a prompt.  */
+  interp_pre_command_loop (top_level_interpreter ());
+
+  /* Now it's time to start the event loop.  */
+  start_event_loop ();
+
+  in_cli = 0;
+
+  Py_RETURN_NONE;
+}
+
+/* Set up the Python argument vector and evaluate a script.  This is
+   used to implement 'gdb -P'.  */
+
+void
+run_python_script (int argc, char **argv)
+{
+  FILE *input;
+
+  /* We never free this, since we plan to exit at the end.  */
+  ensure_python_env (get_current_arch (), current_language);
+
+  running_python_script = 1;
+
+#if PYTHON_ABI_VERSION < 3
+  PySys_SetArgv (argc - 1, argv + 1);
+#else
+  {
+    wchar_t **wargv = (wchar_t **) alloca (sizeof (*wargv) * (argc + 1));
+    int i;
+
+    for (i = 1; i < argc; i++)
+      {
+	size_t len = mbstowcs (NULL, argv[i], 0);
+	/* Python-related GDB sources are built with -DNDEBUG
+	   https://sourceware.org/bugzilla/show_bug.cgi?id=20445 */
+	size_t len2 ATTRIBUTE_UNUSED;
+
+	if (len == (size_t) -1)
+	  {
+	    fprintf (stderr, "Invalid multibyte argument #%d \"%s\"\n",
+		     i, argv[i]);
+	    exit (1);
+	  }
+	wargv[i] = (wchar_t *) alloca (sizeof (**wargv) * (len + 1));
+	len2 = mbstowcs (wargv[i], argv[i], len + 1);
+	assert (len2 == len);
+      }
+    wargv[argc] = NULL;
+    PySys_SetArgv (argc - 1, wargv + 1);
+  }
+#endif
+
+  input = fopen (argv[0], "r");
+  if (! input)
+    {
+      fprintf (stderr, "could not open %s: %s\n", argv[0], strerror (errno));
+      exit (1);
+    }
+  PyRun_SimpleFile (input, argv[0]);
+  fclose (input);
+  exit (0);
+}
+
+
+
 
 static PyObject *
 gdbpy_get_current_progspace (PyObject *unused1, PyObject *unused2)
@@ -2035,6 +2146,8 @@ PyMethodDef python_GdbMethods[] =
 Evaluate command, a string, as a gdb CLI command.  Optionally returns\n\
 a Python String containing the output of the command if to_string is\n\
 set to True." },
+  { "cli", gdbpy_cli, METH_NOARGS,
+    "Enter the gdb CLI" },
   { "parameter", gdbpy_parameter, METH_VARARGS,
     "Return a gdb parameter's value" },
 
diff --git a/gdb/python/python.h b/gdb/python/python.h
index e407faabfd..fc1c6326a2 100644
--- a/gdb/python/python.h
+++ b/gdb/python/python.h
@@ -25,4 +25,6 @@
 /* This is all that python exports to gdb.  */
 extern const struct extension_language_defn extension_language_python;
 
+extern void run_python_script (int argc, char **argv);
+
 #endif /* GDB_PYTHON_H */
diff --git a/gdb/testsuite/gdb.python/py-frame.exp b/gdb/testsuite/gdb.python/py-frame.exp
index f5d4a3cc12..3546f7ba2a 100644
--- a/gdb/testsuite/gdb.python/py-frame.exp
+++ b/gdb/testsuite/gdb.python/py-frame.exp
@@ -95,6 +95,8 @@ gdb_test "python print ('result = %s' % f0.read_var ('a'))" " = 1" "test Frame.r
 
 gdb_test "python print ('result = %s' % (gdb.selected_frame () == f1))" " = True" "test gdb.selected_frame"
 
+gdb_test "python print ('result = %s' % (f0.block ()))" "<gdb.Block object at 0x\[\[:xdigit:\]\]+>" "test Frame.block"
+
 # Can read SP register.
 gdb_test "python print ('result = %s' % (gdb.selected_frame ().read_register ('sp') == gdb.parse_and_eval ('\$sp')))" \
   " = True" \
diff --git a/gdb/testsuite/gdb.python/py-value.exp b/gdb/testsuite/gdb.python/py-value.exp
index 1781887c4a..8a2ddd6fae 100644
--- a/gdb/testsuite/gdb.python/py-value.exp
+++ b/gdb/testsuite/gdb.python/py-value.exp
@@ -384,6 +384,15 @@ proc test_value_after_death {} {
     "print value's type"
 }
 
+# Regression test for a cast failure.  The bug was that if we cast a
+# value to its own type, gdb could crash.  This happened because we
+# could end up double-freeing a struct value.
+proc test_cast_regression {} {
+  gdb_test "python v = gdb.Value(5)" "" "create value for cast test"
+  gdb_test "python v = v.cast(v.type)" "" "cast value for cast test"
+  gdb_test "python print(v)" "5" "print value for cast test"
+}
+
 # Regression test for invalid subscript operations.  The bug was that
 # the type of the value was not being checked before allowing a
 # subscript operation to proceed.
@@ -512,6 +521,7 @@ if ![runto_main] then {
 test_value_in_inferior
 test_inferior_function_call
 test_value_after_death
+test_cast_regression
 
 # Test either C or C++ values. 
 
diff --git a/gdb/varobj.c b/gdb/varobj.c
index 93b97f6f70..753c6596b3 100644
--- a/gdb/varobj.c
+++ b/gdb/varobj.c
@@ -217,6 +217,14 @@ is_root_p (const struct varobj *var)
 }
 
 #ifdef HAVE_PYTHON
+/* Helper function to install a Python environment suitable for
+   use during operations on VAR.  */
+struct cleanup *
+varobj_ensure_python_env (const struct varobj *var)
+{
+  return ensure_python_env (var->root->exp->gdbarch,
+			    var->root->exp->language_defn);
+}
 
 /* See python-internal.h.  */
 gdbpy_enter_varobj::gdbpy_enter_varobj (const struct varobj *var)
diff --git a/gdb/varobj.h b/gdb/varobj.h
index 9163a34fd0..ed51b6ad34 100644
--- a/gdb/varobj.h
+++ b/gdb/varobj.h
@@ -327,6 +327,8 @@ extern bool varobj_has_more (const struct varobj *var, int to);
 
 extern bool varobj_is_dynamic_p (const struct varobj *var);
 
+extern struct cleanup *varobj_ensure_python_env (const struct varobj *var);
+
 extern bool varobj_default_value_is_changeable_p (const struct varobj *var);
 extern bool varobj_value_is_changeable_p (const struct varobj *var);
 
-- 
2.14.3