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

[Khoo Yit Phang <khooyp@cs.umd.edu>]

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Hi,

I've updated my Python/GDB readline patch for the new SIGINT handling patch that you've just checked in, Tom. The only change is that there's no longer any need to swap SIGINT handlers. If it's alright, I'll check it in.

Yit
August 22, 2012


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# HG changeset patch
# Parent 9cf27242c2eadcf990d1dde46c20b21111d837fc
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:

2012-08-22  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 \
@@ -2083,6 +2085,10 @@
 	$(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 +1,113 @@
+/* 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)
+    p = command_line_input (prompt, 0, "python");
+
+  /* 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
@@ -232,6 +232,7 @@
 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
@@ -1389,6 +1389,7 @@
   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 ();