bpo-42923: _Py_DumpExtensionModules() ignores stdlib ext (GH-24254)

Include/internal/pycore_traceback.h

@@ -74,7 +74,7 @@ PyAPI_FUNC(void) _Py_DumpASCII(int fd, PyObject *text);
    This function is signal safe. */
 PyAPI_FUNC(void) _Py_DumpDecimal(
     int fd,
-    unsigned long value);
+    size_t value);
 
 /* Format an integer as hexadecimal with width digits into fd file descriptor.
    The function is signal safe. */

Lib/test/test_capi.py

@@ -547,8 +547,7 @@ class CAPITest(unittest.TestCase):
         self.assertRaises(TypeError, pynumber_tobase, '123', 10)
         self.assertRaises(SystemError, pynumber_tobase, 123, 0)
 
-    def test_fatal_error(self):
-        code = 'import _testcapi; _testcapi.fatal_error(b"MESSAGE")'
+    def check_fatal_error(self, code, expected, not_expected=()):
         with support.SuppressCrashReport():
             rc, out, err = assert_python_failure('-sSI', '-c', code)
 
@@ -556,15 +555,25 @@ class CAPITest(unittest.TestCase):
         self.assertIn('Fatal Python error: test_fatal_error: MESSAGE\n',
                       err)
 
-        match = re.search('^Extension modules:(.*)$', err, re.MULTILINE)
+        match = re.search(r'^Extension modules:(.*) \(total: ([0-9]+)\)$',
+                          err, re.MULTILINE)
         if not match:
             self.fail(f"Cannot find 'Extension modules:' in {err!r}")
         modules = set(match.group(1).strip().split(', '))
-        # Test _PyModule_IsExtension(): the list doesn't have to
-        # be exhaustive.
-        for name in ('sys', 'builtins', '_imp', '_thread', '_weakref',
-                     '_io', 'marshal', '_signal', '_abc', '_testcapi'):
+        total = int(match.group(2))
+
+        for name in expected:
             self.assertIn(name, modules)
+        for name in not_expected:
+            self.assertNotIn(name, modules)
+        self.assertEqual(len(modules), total)
+
+    def test_fatal_error(self):
+        expected = ('_testcapi',)
+        not_expected = ('sys', 'builtins', '_imp', '_thread', '_weakref',
+                        '_io', 'marshal', '_signal', '_abc')
+        code = 'import _testcapi; _testcapi.fatal_error(b"MESSAGE")'
+        self.check_fatal_error(code, expected, not_expected)
 
 
 class TestPendingCalls(unittest.TestCase):

Lib/test/test_faulthandler.py

@@ -334,19 +334,19 @@ class FaultHandlerTests(unittest.TestCase):
     def test_dump_ext_modules(self):
         code = """
             import faulthandler
+            # _testcapi is a test module and not considered as a stdlib module
+            import _testcapi
             faulthandler.enable()
             faulthandler._sigsegv()
             """
         stderr, exitcode = self.get_output(code)
         stderr = '\n'.join(stderr)
-        match = re.search('^Extension modules:(.*)$', stderr, re.MULTILINE)
+        match = re.search(r'^Extension modules:(.*) \(total: [0-9]+\)$',
+                          stderr, re.MULTILINE)
         if not match:
             self.fail(f"Cannot find 'Extension modules:' in {stderr!r}")
         modules = set(match.group(1).strip().split(', '))
-        # Only check for a few extensions, the list doesn't have to be
-        # exhaustive.
-        for ext in ('sys', 'builtins', '_io', 'faulthandler'):
-            self.assertIn(ext, modules)
+        self.assertIn('_testcapi', modules)
 
     def test_is_enabled(self):
         orig_stderr = sys.stderr

Python/pylifecycle.c

@@ -18,6 +18,8 @@
 #include "pycore_sysmodule.h"     // _PySys_ClearAuditHooks()
 #include "pycore_traceback.h"     // _Py_DumpTracebackThreads()
 
+#include "module_names.h"         // _Py_module_names
+
 #include <locale.h>               // setlocale()
 
 #ifdef HAVE_SIGNAL_H
@@ -2496,10 +2498,12 @@ fatal_error_exit(int status)
 }
 
 
-// Dump the list of extension modules of sys.modules into fd file descriptor.
+// Dump the list of extension modules of sys.modules, excluding stdlib modules
+// (_Py_module_names), into fd file descriptor.
+//
 // This function is called by a signal handler in faulthandler: avoid memory
-// allocations and keep the implementation simple. For example, the list
-// is not sorted on purpose.
+// allocations and keep the implementation simple. For example, the list is not
+// sorted on purpose.
 void
 _Py_DumpExtensionModules(int fd, PyInterpreterState *interp)
 {
@@ -2507,15 +2511,14 @@ _Py_DumpExtensionModules(int fd, PyInterpreterState *interp)
         return;
     }
     PyObject *modules = interp->modules;
-    if (!PyDict_Check(modules)) {
+    if (modules == NULL || !PyDict_Check(modules)) {
         return;
     }
 
-    PUTS(fd, "\nExtension modules: ");
-
+    int header = 1;
+    Py_ssize_t count = 0;
     Py_ssize_t pos = 0;
     PyObject *key, *value;
-    int comma = 0;
     while (PyDict_Next(modules, &pos, &key, &value)) {
         if (!PyUnicode_Check(key)) {
             continue;
@@ -2524,15 +2527,42 @@ _Py_DumpExtensionModules(int fd, PyInterpreterState *interp)
             continue;
         }
 
-        if (comma) {
+        // Check if it is a stdlib extension module.
+        // Use the module name from the sys.modules key,
+        // don't attempt to get the module object name.
+        const Py_ssize_t names_len = Py_ARRAY_LENGTH(_Py_module_names);
+        int is_stdlib_mod = 0;
+        for (Py_ssize_t i=0; i < names_len; i++) {
+            const char *name = _Py_module_names[i];
+            if (PyUnicode_CompareWithASCIIString(key, name) == 0) {
+                is_stdlib_mod = 1;
+                break;
+            }
+        }
+        if (is_stdlib_mod) {
+            // Ignore stdlib extension module.
+            continue;
+        }
+
+        if (header) {
+            PUTS(fd, "\nExtension modules: ");
+            header = 0;
+        }
+        else {
             PUTS(fd, ", ");
         }
-        comma = 1;
 
         _Py_DumpASCII(fd, key);
+        count++;
     }
+
+    if (count) {
+        PUTS(fd, " (total: ");
+        _Py_DumpDecimal(fd, count);
+        PUTS(fd, ")");
         PUTS(fd, "\n");
     }
+}
 
 
 static void _Py_NO_RETURN

Python/traceback.c

@@ -628,12 +628,12 @@ PyTraceBack_Print(PyObject *v, PyObject *f)
    This function is signal safe. */
 
 void
-_Py_DumpDecimal(int fd, unsigned long value)
+_Py_DumpDecimal(int fd, size_t value)
 {
     /* maximum number of characters required for output of %lld or %p.
        We need at most ceil(log10(256)*SIZEOF_LONG_LONG) digits,
        plus 1 for the null byte.  53/22 is an upper bound for log10(256). */
-    char buffer[1 + (sizeof(unsigned long)*53-1) / 22 + 1];
+    char buffer[1 + (sizeof(size_t)*53-1) / 22 + 1];
     char *ptr, *end;
 
     end = &buffer[Py_ARRAY_LENGTH(buffer) - 1];
@@ -767,7 +767,7 @@ dump_frame(int fd, PyFrameObject *frame)
     int lineno = PyCode_Addr2Line(code, frame->f_lasti);
     PUTS(fd, ", line ");
     if (lineno >= 0) {
-        _Py_DumpDecimal(fd, (unsigned long)lineno);
+        _Py_DumpDecimal(fd, (size_t)lineno);
     }
     else {
         PUTS(fd, "???");