[not part of build] stack crawl tree

gc/boehm/call_tree.h

@@ -0,0 +1,17 @@
+/*
+    call_tree.h
+ */
+
+#ifndef call_tree_h
+#define call_tree_h
+
+typedef struct call_tree call_tree;
+
+struct call_tree {
+    void* pc;               /* program counter */
+    call_tree* parent;      /* parent node     */
+    call_tree* siblings;    /* next sibling    */
+    call_tree* children;    /* children nodes  */
+};
+
+#endif