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Revert and patch "[Python] Remove readline module"

Fix https://bugs.llvm.org/show_bug.cgi?id=43830 while avoiding polluting the
global Python namespace.

This both reverts r357277 to rebundle a version of Python's readline module
based on libedit.

However, this patch also provides two improvements over the previous
implementation:

1. use PyMem_RawMalloc instead of PyMem_Malloc, as expected by PyOS_Readline
   (prevents to segfault upon exit of interactive session)
2. patch the readline module upon embedded interpreter loading, instead of
   patching it globally, which should prevent any side effect on other
   modules/packages
3. only activate the patched module if libedit is actually linked in lldb

Differential Revision: https://reviews.llvm.org/D69793
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serge-sans-paille
serge-sans-paille committed Nov 5, 2019
1 parent 0e56b0f commit 9357b5d08497326a1895cab6c1d712bf12a34519
@@ -5,6 +5,7 @@ add_definitions(-DLLDB_PYTHON_RELATIVE_LIBDIR="${LLDB_PYTHON_RELATIVE_PATH}")

add_lldb_library(lldbPluginScriptInterpreterPython PLUGIN
PythonDataObjects.cpp
PythonReadline.cpp
ScriptInterpreterPython.cpp

LINK_LIBS
@@ -0,0 +1,80 @@
#include "PythonReadline.h"

#ifdef LLDB_USE_LIBEDIT_READLINE_COMPAT_MODULE

#include <stdio.h>

#include <editline/readline.h>

// Simple implementation of the Python readline module using libedit.
// In the event that libedit is excluded from the build, this turns
// back into a null implementation that blocks the module from pulling
// in the GNU readline shared lib, which causes linkage confusion when
// both readline and libedit's readline compatibility symbols collide.
//
// Currently it only installs a PyOS_ReadlineFunctionPointer, without
// implementing any of the readline module methods. This is meant to
// work around LLVM pr18841 to avoid seg faults in the stock Python
// readline.so linked against GNU readline.
//
// Bug on the cpython side: https://bugs.python.org/issue38634

PyDoc_STRVAR(moduleDocumentation,
"Simple readline module implementation based on libedit.");

#if PY_MAJOR_VERSION >= 3
static struct PyModuleDef readline_module = {
PyModuleDef_HEAD_INIT, // m_base
"lldb_editline", // m_name
moduleDocumentation, // m_doc
-1, // m_size
nullptr, // m_methods
nullptr, // m_reload
nullptr, // m_traverse
nullptr, // m_clear
nullptr, // m_free
};
#else
static struct PyMethodDef moduleMethods[] = {{nullptr, nullptr, 0, nullptr}};
#endif

static char *
#if PY_MAJOR_VERSION >= 3
simple_readline(FILE *stdin, FILE *stdout, const char *prompt)
#else
simple_readline(FILE *stdin, FILE *stdout, char *prompt)
#endif
{
rl_instream = stdin;
rl_outstream = stdout;
char *line = readline(prompt);
if (!line) {
char *ret = (char *)PyMem_RawMalloc(1);
if (ret != NULL)
*ret = '\0';
return ret;
}
if (*line)
add_history(line);
int n = strlen(line);
char *ret = (char *)PyMem_RawMalloc(n + 2);
if (ret) {
strncpy(ret, line, n);
free(line);
ret[n] = '\n';
ret[n + 1] = '\0';
}
return ret;
}

PyMODINIT_FUNC initlldb_readline(void) {
PyOS_ReadlineFunctionPointer = simple_readline;

#if PY_MAJOR_VERSION >= 3
return PyModule_Create(&readline_module);
#else
Py_InitModule4("lldb_readline", moduleMethods, moduleDocumentation,
static_cast<PyObject *>(NULL), PYTHON_API_VERSION);
#endif
}
#endif
@@ -0,0 +1,26 @@
//===-- PythonReadline.h ----------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLDB_PLUGINS_SCRIPTINTERPRETER_PYTHON_PYTHONREADLINE_H
#define LLDB_PLUGINS_SCRIPTINTERPRETER_PYTHON_PYTHONREADLINE_H

#if !defined(LLDB_DISABLE_LIBEDIT) && !defined(__APPLE__)
// NOTE: Since Python may define some pre-processor definitions which affect the
// standard headers on some systems, you must include Python.h before any
// standard headers are included.
#include "Python.h"

// no need to hack into Python's readline module if libedit isn't used.
//
#define LLDB_USE_LIBEDIT_READLINE_COMPAT_MODULE 1

extern "C" PyMODINIT_FUNC initlldb_readline(void);

#endif

#endif // LLDB_PLUGINS_SCRIPTINTERPRETER_PYTHON_PYTHONREADLINE_H
@@ -16,6 +16,7 @@
#include "lldb-python.h"

#include "PythonDataObjects.h"
#include "PythonReadline.h"
#include "ScriptInterpreterPythonImpl.h"

#include "lldb/API/SBFrame.h"
@@ -217,6 +218,22 @@ struct InitializePythonRAII {

InitializePythonHome();

#ifdef LLDB_USE_LIBEDIT_READLINE_COMPAT_MODULE
// Python's readline is incompatible with libedit being linked into lldb.
// Provide a patched version local to the embedded interpreter.
bool ReadlinePatched = false;
for (auto *p = PyImport_Inittab; p->name != NULL; p++) {
if (strcmp(p->name, "readline") == 0) {
p->initfunc = initlldb_readline;
break;
}
}
if (!ReadlinePatched) {
PyImport_AppendInittab("readline", initlldb_readline);
ReadlinePatched = true;
}
#endif

// Register _lldb as a built-in module.
PyImport_AppendInittab("_lldb", LLDBSwigPyInit);

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