python · vstinner · Aug 13, 2026 · Jul 9, 2026
diff --git a/Doc/library/os.rst b/Doc/library/os.rst
@@ -1011,10 +1011,14 @@ as internal buffering of data.
       It will always copy no bytes and return 0 as if the file was empty
       because of a known Linux kernel issue.
 
-   .. availability:: Linux >= 4.5 with glibc >= 2.27.
+   .. availability:: Linux >= 4.5.
 
    .. versionadded:: 3.8
 
+   .. versionchanged:: 3.16
+      The function is now also available when Python is built against a libc
+      that lacks ``copy_file_range()``, such as glibc older than 2.27.
+
 
 .. function:: device_encoding(fd)
 
@@ -4400,10 +4404,14 @@ The following flags are used in :attr:`statvfs_result.f_flag`.
    the file descriptor, and as such multiple files can have the same name
    without any side effects.
 
-   .. availability:: Linux >= 3.17 with glibc >= 2.27.
+   .. availability:: Linux >= 3.17.
 
    .. versionadded:: 3.8
 
+   .. versionchanged:: 3.16
+      The function is now also available when Python is built against a libc
+      that lacks ``memfd_create()``, such as glibc older than 2.27.
+
 
 .. data:: MFD_CLOEXEC
           MFD_ALLOW_SEALING

diff --git a/Misc/NEWS.d/next/Library/2026-08-10-22-23-29.gh-issue-153400.nucElC.rst b/Misc/NEWS.d/next/Library/2026-08-10-22-23-29.gh-issue-153400.nucElC.rst
@@ -0,0 +1,4 @@
+On Linux, :func:`os.copy_file_range` and :func:`os.memfd_create` now fall back
+to the raw syscall when the libc Python is built against does not provide the
+wrapper function, so they stay available on interpreters built against a libc
+older than glibc 2.27.
diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
@@ -157,8 +157,8 @@
 #ifdef HAVE_LINUX_RANDOM_H
 #  include <linux/random.h>       // GRND_RANDOM
 #endif
-#ifdef HAVE_GETRANDOM_SYSCALL
-#  include <sys/syscall.h>        // syscall()
+#ifdef HAVE_SYS_SYSCALL_H
+#  include <sys/syscall.h>        // syscall(), __NR_xxx syscall numbers
 #endif
 
 #ifdef HAVE_POSIX_SPAWN
@@ -13133,7 +13133,12 @@ os_pwritev_impl(PyObject *module, int fd, PyObject *buffers, Py_off_t offset,
 }
 #endif /* HAVE_PWRITEV */
 
-#ifdef HAVE_COPY_FILE_RANGE
+#if defined(HAVE_COPY_FILE_RANGE) || \
+    (defined(__linux__) && defined(__NR_copy_file_range))
+#  define _Py_HAVE_COPY_FILE_RANGE
+#endif
+
+#ifdef _Py_HAVE_COPY_FILE_RANGE
 /*[clinic input]
 
 os.copy_file_range
@@ -13185,7 +13190,13 @@ os_copy_file_range_impl(PyObject *module, int src, int dst, Py_ssize_t count,
 
     do {
         Py_BEGIN_ALLOW_THREADS
+#ifdef HAVE_COPY_FILE_RANGE
         ret = copy_file_range(src, p_offset_src, dst, p_offset_dst, count, flags);
+#else
+        /* Largefile support makes off_t 64-bit, as the kernel expects. */
+        ret = syscall(__NR_copy_file_range, src, p_offset_src, dst, p_offset_dst,
+                      count, flags);
+#endif
         Py_END_ALLOW_THREADS
     } while (ret < 0 && errno == EINTR && !(async_err = PyErr_CheckSignals()));
 
@@ -13195,7 +13206,7 @@ os_copy_file_range_impl(PyObject *module, int src, int dst, Py_ssize_t count,
 
     return PyLong_FromSsize_t(ret);
 }
-#endif /* HAVE_COPY_FILE_RANGE*/
+#endif /* _Py_HAVE_COPY_FILE_RANGE */
 
 #if (defined(HAVE_SPLICE) && !defined(_AIX))
 /*[clinic input]
@@ -15897,7 +15908,12 @@ os_urandom_impl(PyObject *module, Py_ssize_t size)
     return PyBytesWriter_Finish(writer);
 }
 
-#ifdef HAVE_MEMFD_CREATE
+#if defined(HAVE_MEMFD_CREATE) || \
+    (defined(__linux__) && defined(__NR_memfd_create) && defined(MFD_CLOEXEC))
+#  define _Py_HAVE_MEMFD_CREATE
+#endif
+
+#ifdef _Py_HAVE_MEMFD_CREATE
 /*[clinic input]
 os.memfd_create
 
@@ -15913,7 +15929,11 @@ os_memfd_create_impl(PyObject *module, PyObject *name, unsigned int flags)
     int fd;
     const char *bytes = PyBytes_AS_STRING(name);
     Py_BEGIN_ALLOW_THREADS
+#ifdef HAVE_MEMFD_CREATE
     fd = memfd_create(bytes, flags);
+#else
+    fd = syscall(__NR_memfd_create, bytes, flags);
+#endif
     Py_END_ALLOW_THREADS
     if (fd == -1) {
         return PyErr_SetFromErrno(PyExc_OSError);
@@ -18533,7 +18553,7 @@ all_ins(PyObject *m)
     if (PyModule_AddIntMacro(m, GRND_RANDOM)) return -1;
     if (PyModule_AddIntMacro(m, GRND_NONBLOCK)) return -1;
 #endif
-#ifdef HAVE_MEMFD_CREATE
+#ifdef _Py_HAVE_MEMFD_CREATE
     if (PyModule_AddIntMacro(m, MFD_CLOEXEC)) return -1;
     if (PyModule_AddIntMacro(m, MFD_ALLOW_SEALING)) return -1;
 #ifdef MFD_HUGETLB
@@ -18581,7 +18601,7 @@ all_ins(PyObject *m)
 #ifdef MFD_HUGE_16GB
     if (PyModule_AddIntMacro(m, MFD_HUGE_16GB)) return -1;
 #endif
-#endif /* HAVE_MEMFD_CREATE */
+#endif /* _Py_HAVE_MEMFD_CREATE */
 
 #if defined(HAVE_EVENTFD) && defined(EFD_CLOEXEC)
     if (PyModule_AddIntMacro(m, EFD_CLOEXEC)) return -1;
@@ -18837,7 +18857,7 @@ static const struct have_function {
     { "HAVE_LUTIMES", NULL },
 #endif
 
-#ifdef HAVE_MEMFD_CREATE
+#ifdef _Py_HAVE_MEMFD_CREATE
     { "HAVE_MEMFD_CREATE", NULL },
 #endif