Merge pull request adafruit#1816 from tannewt/stage_crash

Correct collect of permanent pointers.

Author: dhalbert

py/gc.c

@@ -345,6 +345,19 @@ STATIC void gc_sweep(void) {
  }
 }
 
+// Mark can handle NULL pointers because it verifies the pointer is within the heap bounds.
+STATIC void gc_mark(void* ptr) {
+ if (VERIFY_PTR(ptr)) {
+ size_t block = BLOCK_FROM_PTR(ptr);
+ if (ATB_GET_KIND(block) == AT_HEAD) {
+ // An unmarked head: mark it, and mark all its children
+ TRACE_MARK(block, ptr);
+ ATB_HEAD_TO_MARK(block);
+ gc_mark_subtree(block);
+ }
+ }
+}
+
 void gc_collect_start(void) {
  GC_ENTER();
  MP_STATE_MEM(gc_lock_depth)++;
@@ -361,9 +374,7 @@ void gc_collect_start(void) {
  size_t root_end = offsetof(mp_state_ctx_t, vm.qstr_last_chunk);
  gc_collect_root(ptrs + root_start / sizeof(void*), (root_end - root_start) / sizeof(void*));
 
- if (MP_STATE_MEM(permanent_pointers) != NULL) {
- gc_collect_root(MP_STATE_MEM(permanent_pointers), BYTES_PER_BLOCK / sizeof(void*));
- }
+ gc_mark(MP_STATE_MEM(permanent_pointers));
 
  #if MICROPY_ENABLE_PYSTACK
  // Trace root pointers from the Python stack.
@@ -375,15 +386,7 @@ void gc_collect_start(void) {
 void gc_collect_root(void **ptrs, size_t len) {
  for (size_t i = 0; i < len; i++) {
  void *ptr = ptrs[i];
- if (VERIFY_PTR(ptr)) {
- size_t block = BLOCK_FROM_PTR(ptr);
- if (ATB_GET_KIND(block) == AT_HEAD) {
- // An unmarked head: mark it, and mark all its children
- TRACE_MARK(block, ptr);
- ATB_HEAD_TO_MARK(block);
- gc_mark_subtree(block);
- }
- }
+ gc_mark(ptr);
  }
 }