gdb/python/py-gdb-readline.c

/* Readline support for Python.

   Copyright (C) 2012-2026 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 "python-internal.h"
#include "top.h"
#include "cli/cli-utils.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,
			const char *prompt)
{
  int n;
  const char *p = NULL;
  std::string buffer;
  char *q;

  try
    {
      p = command_line_input (buffer, prompt, "python");
    }
  /* Handle errors by raising Python exceptions.  */
  catch (const gdb_exception_forced_quit &e)
    {
      quit_force (NULL, 0);
    }
  catch (const gdb_exception &except)
    {
      /* Detect user interrupt (Ctrl-C).  */
      if (except.reason == RETURN_QUIT)
	return NULL;


      /* This readline callback is called without the GIL held.  */
      gdbpy_gil gil;

      return gdbpy_handle_gdb_exception (nullptr, except);
    }

  /* Detect EOF (Ctrl-D).  */
  if (p == NULL)
    {
      q = (char *) PyMem_RawMalloc (1);
      if (q != NULL)
	q[0] = '\0';
      return q;
    }

  n = strlen (p);

  /* Copy the line to Python and return.  */
  q = (char *) PyMem_RawMalloc (n + 2);
  if (q != NULL)
    {
      strcpy (q, p);
      q[n] = '\n';
      q[n + 1] = '\0';
    }
  return q;
}

/* Initialize Python readline support.  */

static int
gdbpy_initialize_gdb_readline ()
{
  /* 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.

     Notes: Python includes three default importers.  As mentioned in the
     documentation [1]:
     - The first one knows how to locate built-in modules.
     - The second one knows how to locate frozen modules.
     - A third default finder searches an import path for modules.
     [1]: https://docs.python.org/3/reference/import.html#finders-and-loaders

     The third default finder is the one that will load readline, so the custom
     finder to disable the import of readline in GDB has to be placed before
     this third default finder.  */
  const char *code = "\
import sys\n\
from importlib.abc import MetaPathFinder\n\
\n\
class GdbRemoveReadlineFinder(MetaPathFinder):\n\
\n\
  def find_spec(self, fullname, path=None, target=None):\n\
    if fullname == \"readline\":\n\
      raise ImportError(\"readline module disabled under GDB\")\n\
\n\
sys.meta_path.insert(2, GdbRemoveReadlineFinder())\n\
";
  if (eval_python_command (code, Py_file_input) == 0)
    PyOS_ReadlineFunctionPointer = gdbpy_readline_wrapper;

  return 0;
}

GDBPY_INITIALIZE_FILE (gdbpy_initialize_gdb_readline);