[PATCH 4/4]: Enable readline under "python"

Khoo Yit Phang
2012-07-16T21:04:33Z

[-- Attachment #1: Type: text/plain, Size: 817 bytes --]

Hi,

Here's the last Python patch: this enables readline support under "python" using a GDB-specific mechanism, and disables the standard Python readline module.

This is somewhat of a workaround: unfortunately, there is no easy way to make GDB and Python use libreadline without conflicting with each other, since libreadline is configured essentially using global variables. Using the standard Python readline module will lead to strange conflicts, e.g., changing key bindings or tab-completion. I've thought of two possible solutions which are both rather complicated: 1) either reimplement the readline module that carefully swaps configurations between GDB and Python; 2) or run Python's readline in a separate controlling terminal with a proxy readline module in GDB.

Thank you,

Yit
July 16, 2012

[-- Attachment #2: python-enable-readline --]
[-- Type: application/octet-stream, Size: 6127 bytes --]

# HG changeset patch
# Parent a7e89526afbe05cf717e55ca3a4bf3492efa3001
Provide a GDB-specific readline in Python, blocking the standard Python readline module using a sys.meta_path loader to prevent conflicts with GDB.

gdb/ChangeLog:

2012-07-16 Khoo Yit Phang <khooyp@cs.umd.edu>

Enable readline in Python in a GDB-specific way and block the
standard Python readline module to prevent conflicts with GDB.
* Makefile.in (SUBDIR_PYTHON_OBS): Add py-gdb-readline.o.
(SUBDIR_PYTHON_SRCS): Add python/py-gdb-readline.c.
(py-gdb-readline.o): Add rule to compile python/py-gdb-readline.c.
* python/py-gdb-readline.c: New file.
* python/python-internal.h (gdbpy_initialize_gdb_readline): New
prototype.
* python/python.c (_initialize_python): Call
gdbpy_initialize_gdb_readline.

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -280,6 +280,7 @@
py-finishbreakpoint.o \
py-frame.o \
py-function.o \
+ py-gdb-readline.o \
py-inferior.o \
py-infthread.o \
py-lazy-string.o \
@@ -312,6 +313,7 @@
python/py-finishbreakpoint.c \
python/py-frame.c \
python/py-function.c \
+ python/py-gdb-readline.c \
python/py-inferior.c \
python/py-infthread.c \
python/py-lazy-string.c \
@@ -2082,6 +2084,10 @@
$(COMPILE) $(PYTHON_CFLAGS) $(srcdir)/python/py-function.c
$(POSTCOMPILE)

+py-gdb-readline.o: $(srcdir)/python/py-gdb-readline.c
+ $(COMPILE) $(PYTHON_CFLAGS) $(srcdir)/python/py-gdb-readline.c
+ $(POSTCOMPILE)
+
py-inferior.o: $(srcdir)/python/py-inferior.c
$(COMPILE) $(PYTHON_CFLAGS) $(srcdir)/python/py-inferior.c
$(POSTCOMPILE)
diff --git a/gdb/python/py-gdb-readline.c b/gdb/python/py-gdb-readline.c
new file mode 100644
--- /dev/null
+++ b/gdb/python/py-gdb-readline.c
@@ -0,0 +1,118 @@
+/* Readline support for Python.
+
+ Copyright (C) 2012 Free Software Foundation, Inc.
+
+ This file is part of GDB.
+
+ 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/>. */
+
+#include "defs.h"
+#include "python-internal.h"
+#include "exceptions.h"
+#include "top.h"
+#include "cli/cli-utils.h"
+#include "gdb_string.h"
+
+#include <stddef.h>
+
+/* Readline function suitable for PyOS_ReadlineFunctionPointer, which
+ is used for Python's interactive parser and raw_input. In both
+ cases, sys_stdin and sys_stdout are always stdin and stdout
+ respectively, as far as I can tell; they are ignored and
+ command_line_input is used instead. */
+
+static char *
+gdbpy_readline_wrapper (FILE *sys_stdin, FILE *sys_stdout,
+ char *prompt)
+{
+ int n;
+ char *p = NULL, *p_start, *p_end, *q;
+ volatile struct gdb_exception except;
+
+ TRY_CATCH (except, RETURN_MASK_ALL)
+ {
+ struct cleanup *cleanup = gdbpy_suspend_sigint_handler ();
+
+ p = command_line_input (prompt, 0, "python");
+ do_cleanups (cleanup);
+ }
+
+ /* Detect user interrupt (Ctrl-C). */
+ if (except.reason == RETURN_QUIT)
+ return NULL;
+
+ /* Handle errors by raising Python exceptions. */
+ if (except.reason < 0)
+ {
+ /* The thread state is nulled during gdbpy_readline_wrapper,
+ with the original value saved in the following undocumented
+ variable (see Python's Parser/myreadline.c and
+ Modules/readline.c). */
+ PyEval_RestoreThread (_PyOS_ReadlineTState);
+ gdbpy_convert_exception (except);
+ PyEval_SaveThread ();
+ return NULL;
+ }
+
+ /* Detect EOF (Ctrl-D). */
+ if (p == NULL)
+ {
+ q = PyMem_Malloc (1);
+ if (q != NULL)
+ q[0] = '\0';
+ return q;
+ }
+
+ n = strlen (p);
+
+ /* Copy the line to Python and return. */
+ q = PyMem_Malloc (n + 2);
+ if (q != NULL)
+ {
+ strncpy (q, p, n);
+ q[n] = '\n';
+ q[n + 1] = '\0';
+ }
+ return q;
+}
+
+/* Initialize Python readline support. */
+
+void
+gdbpy_initialize_gdb_readline (void)
+{
+ /* Python's readline module conflicts with GDB's use of readline
+ since readline is not reentrant. Ideally, a reentrant wrapper to
+ GDB's readline should be implemented to replace Python's readline
+ and prevent conflicts. For now, this file implements a
+ sys.meta_path finder that simply fails to import the readline
+ module. */
+ PyRun_SimpleString ("\
+import sys\n\
+\n\
+class GdbRemoveReadlineFinder:\n\
+ def find_module(self, fullname, path=None):\n\
+ if fullname == 'readline' and path is None:\n\
+ return self\n\
+ return None\n\
+\n\
+ def load_module(self, fullname):\n\
+ raise ImportError('readline module disabled under GDB')\n\
+\n\
+sys.meta_path.append(GdbRemoveReadlineFinder())\n\
+");
+
+ PyOS_ReadlineFunctionPointer = gdbpy_readline_wrapper;
+}
+
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -235,6 +235,7 @@
struct symtab_and_line *sal_object_to_symtab_and_line (PyObject *obj);
struct frame_info *frame_object_to_frame_info (PyObject *frame_obj);

+void gdbpy_initialize_gdb_readline (void);
void gdbpy_initialize_auto_load (void);
void gdbpy_initialize_values (void);
void gdbpy_initialize_frames (void);
diff --git a/gdb/python/python.c b/gdb/python/python.c
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -1403,6 +1403,7 @@
gdbpy_gdberror_exc = PyErr_NewException ("gdb.GdbError", NULL, NULL);
PyModule_AddObject (gdb_module, "GdbError", gdbpy_gdberror_exc);

+ gdbpy_initialize_gdb_readline ();
gdbpy_initialize_auto_load ();
gdbpy_initialize_values ();
gdbpy_initialize_frames ();