darwin: use runtime check for file cloning

Using #ifdef guards is not reliable because libuv may have been compiled
on a newer system than what it runs on, or vice versa.

Fixes: libuv#2088
Fixes: nodejs/node#24521

src/unix/fs.c

@@ -61,6 +61,7 @@
 
 #if defined(__APPLE__)
 # include <copyfile.h>
+# include <sys/sysctl.h>
 #elif defined(__linux__) && !defined(FICLONE)
 # include <sys/ioctl.h>
 # define FICLONE _IOW(0x94, 9, int)
@@ -793,26 +794,40 @@ static ssize_t uv__fs_write(uv_fs_t* req) {
 static ssize_t uv__fs_copyfile(uv_fs_t* req) {
 #if defined(__APPLE__) && !TARGET_OS_IPHONE
   /* On macOS, use the native copyfile(3). */
+  static int can_clone;
   copyfile_flags_t flags;
+  char buf[64];
+  size_t len;
+  int major;
 
   flags = COPYFILE_ALL;
 
   if (req->flags & UV_FS_COPYFILE_EXCL)
     flags |= COPYFILE_EXCL;
 
-#ifdef COPYFILE_CLONE
-  if (req->flags & UV_FS_COPYFILE_FICLONE)
-    flags |= COPYFILE_CLONE;
-#endif
+  /* Check OS version. Cloning is only supported on macOS >= 10.12. */
+  if (req->flags & (UV_FS_COPYFILE_FICLONE|UV_FS_COPYFILE_FICLONE_FORCE)) {
+    if (can_clone == 0) {
+      len = sizeof(buf);
+      if (sysctlbyname("kern.osrelease", buf, &len, NULL, 0))
+        return UV__ERR(errno);
 
-  if (req->flags & UV_FS_COPYFILE_FICLONE_FORCE) {
-#ifdef COPYFILE_CLONE_FORCE
-    flags |= COPYFILE_CLONE_FORCE;
-#else
-    return UV_ENOSYS;
-#endif
+      if (1 != sscanf(buf, "%d", &major))
+        abort();
+
+      can_clone = -1 + 2 * (major >= 16);  /* macOS >= 10.12 */
+    }
+
+    if (can_clone < 0)
+      return UV_ENOSYS;
   }
 
+  if (req->flags & UV_FS_COPYFILE_FICLONE)
+    flags |= 1 << 24;  /* COPYFILE_CLONE */
+
+  if (req->flags & UV_FS_COPYFILE_FICLONE_FORCE)
+    flags |= 1 << 25;  /* COPYFILE_CLONE_FORCE */
+
   return copyfile(req->path, req->new_path, NULL, flags);
 #else
   uv_fs_t fs_req;