[3.15] gh-158893: Make os.strerror() thread-safe (#159120)

* gh-157695: Parse also _Py_HAVE_xxx variables in sysconfig (#158926)

Add parse_config_h() tests to test_sysconfig.

(cherry picked from commit 978a8be)

* gh-158893: Make os.strerror() thread-safe (#158927)

Make os.strerror() thread-safe: use the reentrant strerror_r()
function if available.

* The configure script now checks if strerror_r() is supported.
* Add a stress test to test_free_threading.test_os (new module).
* Add a comment on decode_current_locale() assertion which fails if
  the input string is mutated.
* Add an assertion to _Py_DecodeLocale() to detect if the input
  string was mutated during the function call.

* gh-158893: Add internal _Py_strerror() function (#158982)

Add a new internal _Py_strerror() function to Python/fileutils.c. It
uses strerror_r() if available, or use strerror() otherwise.

Replace all strerror(code) calls with _Py_strerror(code).

(cherry picked from commit 15dd735)

Author: vstinner

Include/internal/pycore_fileutils.h

@@ -314,6 +314,9 @@ extern int _Py_GetTicksPerSecond(long *ticks_per_second);
 // Export for '_testcapi' shared extension
 PyAPI_FUNC(int) _Py_IsValidFD(int fd);
 
+// Export for '_remote_debugging' shared extension
+PyAPI_FUNC(PyObject*) _Py_strerror(int code);
+
 #ifdef __cplusplus
 }
 #endif

Lib/sysconfig/__init__.py

@@ -435,9 +435,10 @@ def parse_config_h(fp, vars=None):
     if vars is None:
         vars = {}
     import re
-    define_rx = re.compile("#define ([A-Z][A-Za-z0-9_]+) (.*)\n")
-    undef_rx = re.compile("/[*] #undef ([A-Z][A-Za-z0-9_]+) [*]/\n")
-    quoted_re = re.compile('^"(.*)"$')
+    name_rx = '(?:[A-Z]|_Py_)[A-Za-z0-9_]+'
+    define_rx = re.compile(fr"#define ({name_rx}) (.*)\n")
+    undef_rx = re.compile(fr"/[*] #undef ({name_rx}) [*]/\n")
+    quoted_re = re.compile(r'"(.*)"')
 
     while True:
         line = fp.readline()
@@ -446,7 +447,7 @@ def parse_config_h(fp, vars=None):
         m = define_rx.match(line)
         if m:
             n, v = m.group(1, 2)
-            if mq := quoted_re.match(v):
+            if mq := quoted_re.fullmatch(v):
                 v = mq.group(1)
             try:
                 if n in _ALWAYS_STR:

Lib/test/test_free_threading/test_os.py

@@ -0,0 +1,36 @@
+import errno
+import os
+import sysconfig
+import unittest
+
+from test.support import threading_helper
+from test.support.threading_helper import run_concurrently
+
+
+NTHREADS = 10
+
+
+@threading_helper.requires_working_threading()
+class TestOs(unittest.TestCase):
+    @unittest.skipUnless(sysconfig.get_config_var('_Py_HAVE_STRERROR_R'),
+                         'need _Py_HAVE_STRERROR_R macro')
+    def test_strerror(self):
+        # gh-158893: os.strerror() is implemented with strerror_r() which is
+        # thread safe. Well, check if it's actually the case.
+        last_error = max([getattr(errno, name) for name in dir(errno)
+                          if name.startswith('E')])
+        test_errors = tuple(range(1, last_error + 1))
+        loops = 20
+
+        def worker():
+            for _ in range(loops):
+                for i in test_errors:
+                    os.strerror(i)
+
+        run_concurrently(
+            worker_func=worker, nthreads=NTHREADS
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()

Lib/test/test_sysconfig.py

@@ -29,7 +29,7 @@
                        get_path, get_path_names, _INSTALL_SCHEMES,
                        get_default_scheme, get_scheme_names, get_config_var,
                        _expand_vars, _get_preferred_schemes,
-                       is_python_build, _PROJECT_BASE)
+                       is_python_build, _PROJECT_BASE, parse_config_h)
 from sysconfig.__main__ import _main, _parse_makefile, _get_pybuilddir, _get_json_data_name
 import _imp
 import _osx_support
@@ -760,6 +760,72 @@ def test_sysconfig_config_vars_no_prefix_cache(self):
         self.assertEqual(config_vars['exec_prefix'], sys.exec_prefix)
         self.assertEqual(config_vars['platbase'], sys.exec_prefix)
 
+    def test_parse_config_h(self):
+        config = textwrap.dedent('''
+            #ifndef Py_PYCONFIG_H
+            #define Py_PYCONFIG_H
+
+            /* C comment */
+
+            #define ALIGNOF_LONG 8
+            #define HAVE_ACCEPT 1
+            #define _Py_HAVE_COSPI 1
+            #define INVALID_NUMBER abc
+            #define ALT_SOABI "cpython-316t-x86_64-linux-gnu"
+
+            // Undef macros must be written as "/* #undef NAME */":
+            // name must be valid and there is not value.
+            /* #undef ANDROID_API_LEVEL */
+            #undef IGNORE_UNDEF
+            /* #undef IGNORE_VALUE 1 */
+
+            # _ALWAYS_STR: don't convert values to an integer,
+            # but quotes are removed
+            #define IPHONEOS_DEPLOYMENT_TARGET "13.0"
+            #define MACOSX_DEPLOYMENT_TARGET 10
+
+            // Spaces are tolerated after the name, not before
+            #define SPACES_AFTER    1
+            #define    IGNORED_SPACES_BEFORE 1
+
+            // Ignore macro without value
+            #define IGNORE_NO_VALUE
+
+            // Ignore macros with an invalid name
+            #define _PRIVATE_IGNORED 1
+            #define aLOWER_IGNORED 1
+            #define 123IGNORED 1
+            #define INVALID-NAME 1
+            #define INVALID#NAME 1
+            #define NONASCII_NAME_é 1
+
+            // Ignore single letter names
+            #define A 1
+            /* #undef A */
+
+            #endif /*Py_PYCONFIG_H*/
+        ''')
+
+        filename = TESTFN
+        self.addCleanup(unlink, filename)
+        with open(filename, "w", encoding="utf-8") as fp:
+            fp.write(config)
+        vars = {}
+        with open(filename, encoding="utf-8") as fp:
+            parse_config_h(fp, vars)
+        expected = {
+            'ALIGNOF_LONG': 8,
+            'HAVE_ACCEPT': 1,
+            '_Py_HAVE_COSPI': 1,
+            'INVALID_NUMBER': 'abc',
+            'ALT_SOABI': 'cpython-316t-x86_64-linux-gnu',
+            'ANDROID_API_LEVEL': 0,
+            'IPHONEOS_DEPLOYMENT_TARGET': '13.0',
+            'MACOSX_DEPLOYMENT_TARGET': '10',  # str, not int
+            'SPACES_AFTER': 1,
+        }
+        self.assertEqual(vars, expected)
+
 
 class MakefileTests(unittest.TestCase):
 

Misc/NEWS.d/next/Library/2026-10-06-20-03-01.gh-issue-158893.B6A53q.rst

@@ -0,0 +1,2 @@
+Make :func:`os.strerror` thread-safe: use the reentrant ``strerror_r()``
+function if available. Patch by Victor Stinner.

Modules/_remote_debugging/subprocess.c

@@ -6,6 +6,7 @@
  ******************************************************************************/
 
 #include "_remote_debugging.h"
+#include "pycore_fileutils.h"     // _Py_strerror()
 
 #ifndef MS_WINDOWS
 #include <unistd.h>
@@ -229,9 +230,13 @@ get_child_pids_platform(pid_t target_pid, int recursive, pid_array_t *result)
         if (entry == NULL) {
             if (errno != 0) {
                 int err = errno;
-                _set_debug_oserror_from_errno_with_filename(err, "/proc",
-                    "Failed to read process directory '/proc': %s",
-                    strerror(err));
+                PyObject *message = _Py_strerror(err);
+                if (message != NULL) {
+                    _set_debug_oserror_from_errno_with_filename(err, "/proc",
+                        "Failed to read process directory '/proc': %S",
+                        message);
+                    Py_DECREF(message);
+                }
                 goto done;
             }
             break;
@@ -259,9 +264,13 @@ get_child_pids_platform(pid_t target_pid, int recursive, pid_array_t *result)
     if (closedir(proc_dir) != 0) {
         int err = errno;
         proc_dir = NULL;
-        _set_debug_oserror_from_errno_with_filename(err, "/proc",
-            "Failed to close process directory '/proc': %s",
-            strerror(err));
+        PyObject *message = _Py_strerror(err);
+        if (message != NULL) {
+            _set_debug_oserror_from_errno_with_filename(err, "/proc",
+                "Failed to close process directory '/proc': %S",
+                message);
+            Py_DECREF(message);
+        }
         goto done;
     }
     proc_dir = NULL;

Modules/_remote_debugging/threads.c

@@ -6,6 +6,7 @@
  ******************************************************************************/
 
 #include "_remote_debugging.h"
+#include "pycore_fileutils.h"     // _Py_strerror()
 
 #ifndef MS_WINDOWS
 #include <unistd.h>
@@ -680,9 +681,13 @@ read_thread_ids(RemoteUnwinderObject *unwinder, _Py_RemoteDebug_ThreadsState *st
                 int err = errno;
                 closedir(dir);
                 _Py_RemoteDebug_InitThreadsState(unwinder, st);
-                _set_debug_oserror_from_errno_with_filename(err, task_path,
-                    "Failed to read process task directory '%s': %s",
-                    task_path, strerror(err));
+                PyObject *message = _Py_strerror(err);
+                if (message != NULL) {
+                    _set_debug_oserror_from_errno_with_filename(err, task_path,
+                        "Failed to read process task directory '%s': %S",
+                        task_path, message);
+                    Py_DECREF(message);
+                }
                 return -1;
             }
             break;
@@ -713,9 +718,13 @@ read_thread_ids(RemoteUnwinderObject *unwinder, _Py_RemoteDebug_ThreadsState *st
     if (closedir(dir) != 0) {
         int err = errno;
         _Py_RemoteDebug_InitThreadsState(unwinder, st);
-        _set_debug_oserror_from_errno_with_filename(err, task_path,
-            "Failed to close process task directory '%s': %s",
-            task_path, strerror(err));
+        PyObject *message = _Py_strerror(err);
+        if (message != NULL) {
+            _set_debug_oserror_from_errno_with_filename(err, task_path,
+                "Failed to close process task directory '%s': %S",
+                task_path, message);
+            Py_DECREF(message);
+        }
         return -1;
     }
     st->tids = unwinder->thread_tids;
@@ -780,8 +789,12 @@ _Py_RemoteDebug_StopAllThreads(RemoteUnwinderObject *unwinder, _Py_RemoteDebug_T
         }
         if (ret < 0) {
             detach_threads(st, seized);
-            _set_debug_oserror_from_errno(err,
-                "Failed to seize thread %d: %s", tid, strerror(err));
+            PyObject *message = _Py_strerror(err);
+            if (message != NULL) {
+                _set_debug_oserror_from_errno(err,
+                    "Failed to seize thread %d: %S", tid, message);
+                Py_DECREF(message);
+            }
             _Py_RemoteDebug_InitThreadsState(unwinder, st);
             return -1;
         }
@@ -791,8 +804,12 @@ _Py_RemoteDebug_StopAllThreads(RemoteUnwinderObject *unwinder, _Py_RemoteDebug_T
             err = errno;
             if (err != ESRCH) {
                 detach_threads(st, seized);
-                _set_debug_oserror_from_errno(err,
-                    "Failed to interrupt thread %d: %s", tid, strerror(err));
+                PyObject *message = _Py_strerror(err);
+                if (message != NULL) {
+                    _set_debug_oserror_from_errno(err,
+                        "Failed to interrupt thread %d: %S", tid, message);
+                    Py_DECREF(message);
+                }
                 _Py_RemoteDebug_InitThreadsState(unwinder, st);
                 return -1;
             }
@@ -803,8 +820,12 @@ _Py_RemoteDebug_StopAllThreads(RemoteUnwinderObject *unwinder, _Py_RemoteDebug_T
             err = errno;
             if (err != ECHILD && err != ESRCH) {
                 detach_threads(st, seized);
-                _set_debug_oserror_from_errno(err,
-                    "waitpid failed for thread %d: %s", tid, strerror(err));
+                PyObject *message = _Py_strerror(err);
+                if (message != NULL) {
+                    _set_debug_oserror_from_errno(err,
+                        "waitpid failed for thread %d: %S", tid, message);
+                    Py_DECREF(message);
+                }
                 _Py_RemoteDebug_InitThreadsState(unwinder, st);
                 return -1;
             }

Modules/posixmodule.c

@@ -13831,13 +13831,7 @@ static PyObject *
 os_strerror_impl(PyObject *module, int code)
 /*[clinic end generated code: output=baebf09fa02a78f2 input=75a8673d97915a91]*/
 {
-    char *message = strerror(code);
-    if (message == NULL) {
-        PyErr_SetString(PyExc_ValueError,
-                        "strerror() argument out of range");
-        return NULL;
-    }
-    return PyUnicode_DecodeLocale(message, "surrogateescape");
+    return _Py_strerror(code);
 }
 
 

Python/errors.c

@@ -829,8 +829,7 @@ PyErr_SetFromErrnoWithFilenameObjects(PyObject *exc, PyObject *filenameObject, P
 
 #ifndef MS_WINDOWS
     if (i != 0) {
-        const char *s = strerror(i);
-        message = PyUnicode_DecodeLocale(s, "surrogateescape");
+        message = _Py_strerror(i);
     }
     else {
         /* Sometimes errno didn't get set */