py/runtime: Fix mp_unpack_ex so seq can't be reclaimed by GC during use.
The issue described in the comment added here can be seen by forcing a
gc_collect() at the start of each call to gc_alloc().
@@ -875,8 +875,12 @@ void mp_unpack_ex(mp_obj_t seq_in, size_t num_in, mp_obj_t *items) {
DEBUG_OP_printf("unpack ex " UINT_FMT " " UINT_FMT "\n", num_left, num_right);
size_t seq_len;
if (mp_obj_is_type(seq_in, &mp_type_tuple) || mp_obj_is_type(seq_in, &mp_type_list)) {
+ // Make the seq variable volatile so the compiler keeps a reference to it,
+ // since if it's a tuple then seq_items points to the interior of the GC cell
+ // and mp_obj_new_list may trigger a GC which doesn't trace this and reclaims seq.
+ volatile mp_obj_t seq = seq_in;
mp_obj_t *seq_items;
- mp_obj_get_array(seq_in, &seq_len, &seq_items);
+ mp_obj_get_array(seq, &seq_len, &seq_items);
if (seq_len < num_left + num_right) {
goto too_short;
}
@@ -887,6 +891,7 @@ void mp_unpack_ex(mp_obj_t seq_in, size_t num_in, mp_obj_t *items) {
for (size_t i = 0; i < num_left; i++) {
items[num_right + 1 + i] = seq_items[num_left - 1 - i];
}
+ seq = MP_OBJ_NULL;
} else {
// Generic iterable; this gets a bit messy: we unpack known left length to the
// items destination array, then the rest to a dynamically created list. Once the
