2 files changed, 13 insertions, 0 deletions
diff --git a/py/gc.c b/py/gc.c
index 7ed53cfc7..ca977ce09 100644
--- a/py/gc.c
+++ b/py/gc.c
@@ -392,6 +392,16 @@ void gc_info(gc_info_t *info) {
     GC_EXIT();
 }
 
+void gc_mark_block(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 push it on gc stack */
+            ATB_HEAD_TO_MARK(_block);
+        }
+    }
+}
+
 void *gc_alloc(size_t n_bytes, bool has_finaliser) {
     size_t n_blocks = ((n_bytes + BYTES_PER_BLOCK - 1) & (~(BYTES_PER_BLOCK - 1))) / BYTES_PER_BLOCK;
     DEBUG_printf("gc_alloc(" UINT_FMT " bytes -> " UINT_FMT " blocks)\n", n_bytes, n_blocks);
diff --git a/py/gc.h b/py/gc.h
index 7d8fe2bf8..64c478996 100644
--- a/py/gc.h
+++ b/py/gc.h
@@ -45,6 +45,9 @@ void gc_collect_start(void);
 void gc_collect_root(void **ptrs, size_t len);
 void gc_collect_end(void);
 
+// During a collect, use this to mark blocks used in C but allocated using gc_alloc.
+void gc_mark_block(void * ptr);
+
 void *gc_alloc(size_t n_bytes, bool has_finaliser);
 void gc_free(void *ptr); // does not call finaliser
 size_t gc_nbytes(const void *ptr);