avoid os.stat() int overflow on smallint-only builds

dhalbert · dhalbert · commit e0753c4ad2a2 · 2020-02-14T18:33:37.000-05:00
diff --git a/extmod/vfs_fat.c b/extmod/vfs_fat.c
@@ -345,24 +345,31 @@ STATIC mp_obj_t fat_vfs_stat(mp_obj_t vfs_in, mp_obj_t path_in) {
     } else {
         mode |= MP_S_IFREG;
     }
-    mp_uint_t seconds = timeutils_seconds_since_epoch(
-        1980 + ((fno.fdate >> 9) & 0x7f),
-        (fno.fdate >> 5) & 0x0f,
-        fno.fdate & 0x1f,
-        (fno.ftime >> 11) & 0x1f,
-        (fno.ftime >> 5) & 0x3f,
-        2 * (fno.ftime & 0x1f)
-    );
+#if MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_NONE
+    // On non-longint builds, the number of seconds since 1970 (epoch) is too
+    // large to fit in a smallint, so just return 31-DEC-1999 (0).
+    mp_obj_t seconds = MP_OBJ_NEW_SMALL_INT(946684800);
+#else
+    mp_obj_t seconds = mp_obj_new_int_from_uint(
+        timeutils_seconds_since_epoch(
+            1980 + ((fno.fdate >> 9) & 0x7f),
+            (fno.fdate >> 5) & 0x0f,
+            fno.fdate & 0x1f,
+            (fno.ftime >> 11) & 0x1f,
+            (fno.ftime >> 5) & 0x3f,
+            2 * (fno.ftime & 0x1f)
+            ));
+#endif
     t->items[0] = MP_OBJ_NEW_SMALL_INT(mode); // st_mode
     t->items[1] = MP_OBJ_NEW_SMALL_INT(0); // st_ino
     t->items[2] = MP_OBJ_NEW_SMALL_INT(0); // st_dev
     t->items[3] = MP_OBJ_NEW_SMALL_INT(0); // st_nlink
     t->items[4] = MP_OBJ_NEW_SMALL_INT(0); // st_uid
     t->items[5] = MP_OBJ_NEW_SMALL_INT(0); // st_gid
     t->items[6] = mp_obj_new_int_from_uint(fno.fsize); // st_size
-    t->items[7] = mp_obj_new_int_from_uint(seconds); // st_atime
-    t->items[8] = mp_obj_new_int_from_uint(seconds); // st_mtime
-    t->items[9] = mp_obj_new_int_from_uint(seconds); // st_ctime
+    t->items[7] = seconds;                 // st_atime
+    t->items[8] = seconds;                 // st_mtime
+    t->items[9] = seconds;                 // st_ctime
 
     return MP_OBJ_FROM_PTR(t);
 }
diff --git a/shared-bindings/os/__init__.c b/shared-bindings/os/__init__.c
@@ -143,6 +143,11 @@ MP_DEFINE_CONST_FUN_OBJ_1(os_rmdir_obj, os_rmdir);
 //|
 //|   Get the status of a file or directory.
 //|
+//|   .. note:: On builds without long integers, the number of seconds
+//|      for contemporary dates will not fit in a small integer.
+//|      So the time fields return 946684800,
+//|      which is the number of seconds corresponding to 1999-12-31.
+//|
 mp_obj_t os_stat(mp_obj_t path_in) {
     const char *path = mp_obj_str_get_str(path_in);
     return common_hal_os_stat(path);
