Enable os.copy_file_range via a weak symbol

cpython-unix/build-cpython.sh

@@ -610,6 +610,19 @@ if [[ -n "${LINUX_UAPI_INCLUDE_ARCH:-}" && "${TARGET_TRIPLE}" == *-linux-gnu* ]]
     CONFIGURE_FLAGS="${CONFIGURE_FLAGS} ac_cv_func_memfd_create=yes"
 fi
 
+# Some glibc sysroots predate the copy_file_range() wrapper. Force the
+# configure check on and weak-link the wrapper so the function is exposed only
+# when runtime glibc provides it.
+if [[ "${TARGET_TRIPLE}" == *-linux-gnu* ]]; then
+    if [[ -n "${PYTHON_MEETS_MINIMUM_VERSION_3_14}" ]]; then
+        patch -p1 -i "${ROOT}/patch-posixmodule-copy-file-range-weak.patch"
+    else
+        patch -p1 -i "${ROOT}/patch-posixmodule-copy-file-range-weak-3.13.patch"
+    fi
+
+    CONFIGURE_FLAGS="${CONFIGURE_FLAGS} ac_cv_func_copy_file_range=yes"
+fi
+
 # Define the base PGO profiling task, which we'll extend below with ignores
 export PROFILE_TASK='-m test --pgo'
 

cpython-unix/patch-posixmodule-copy-file-range-weak-3.13.patch

@@ -0,0 +1,31 @@
+diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
+--- a/Modules/posixmodule.c
++++ b/Modules/posixmodule.c
+@@ -10431,4 +10431,9 @@
+ #ifdef HAVE_COPY_FILE_RANGE
++/* Weak references. */
++__attribute__((weak))
++ssize_t copy_file_range(int src, off_t *offset_src, int dst,
++                        off_t *offset_dst, size_t count, unsigned int flags);
++
+ /*[clinic input]
+
+ os.copy_file_range
+@@ -15737,5 +15742,17 @@ posixmodule_exec(PyObject *m)
+ #endif
+
++#ifdef HAVE_COPY_FILE_RANGE
++    if (copy_file_range == NULL) {
++        PyObject *dict = PyModule_GetDict(m);
++        if (dict == NULL) {
++            return -1;
++        }
++        if (PyDict_DelItemString(dict, "copy_file_range") < 0) {
++            return -1;
++        }
++    }
++#endif
++
+     /* Initialize environ dictionary */
+     PyObject *v = convertenviron();
+     Py_XINCREF(v);

cpython-unix/patch-posixmodule-copy-file-range-weak.patch

@@ -0,0 +1,31 @@
+diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
+--- a/Modules/posixmodule.c
++++ b/Modules/posixmodule.c
+@@ -12488,4 +12488,9 @@
+ #ifdef HAVE_COPY_FILE_RANGE
++/* Weak references. */
++__attribute__((weak))
++ssize_t copy_file_range(int src, off_t *offset_src, int dst,
++                        off_t *offset_dst, size_t count, unsigned int flags);
++
+ /*[clinic input]
+
+ os.copy_file_range
+@@ -18147,5 +18152,17 @@ posixmodule_exec(PyObject *m)
+ #endif
+
++#ifdef HAVE_COPY_FILE_RANGE
++    if (copy_file_range == NULL) {
++        PyObject *dict = PyModule_GetDict(m);
++        if (dict == NULL) {
++            return -1;
++        }
++        if (PyDict_PopString(dict, "copy_file_range", NULL) < 0) {
++            return -1;
++        }
++    }
++#endif
++
+     /* Initialize environ dictionary */
+     if (PyModule_Add(m, "environ", convertenviron()) != 0) {
+         return -1;

pythonbuild/disttests/__init__.py

@@ -388,6 +388,38 @@ def test_os_memfd_create(self):
         finally:
             os.close(fd)
 
+    @unittest.skipUnless(
+        "-linux-gnu" in os.environ["TARGET_TRIPLE"],
+        "copy_file_range weak linking is enabled for Linux GNU targets",
+    )
+    def test_os_copy_file_range(self):
+        import ctypes
+        import errno
+
+        libc = ctypes.CDLL(None)
+        libc_has_copy_file_range = hasattr(libc, "copy_file_range")
+        self.assertEqual(hasattr(os, "copy_file_range"), libc_has_copy_file_range)
+
+        if not libc_has_copy_file_range:
+            return
+
+        data = b"copy_file_range"
+        with tempfile.TemporaryFile() as src, tempfile.TemporaryFile() as dst:
+            src.write(data)
+            src.flush()
+            src.seek(0)
+
+            try:
+                copied = os.copy_file_range(src.fileno(), dst.fileno(), len(data))
+            except OSError as exc:
+                if exc.errno == errno.ENOSYS:
+                    self.skipTest("the runtime kernel does not support copy_file_range")
+                raise
+
+            self.assertEqual(copied, len(data))
+            dst.seek(0)
+            self.assertEqual(dst.read(), data)
+
     def test_linux_uapi_not_in_sysconfig(self):
         import sysconfig