1 files changed, 65 insertions, 0 deletions
diff --git a/gc/include/gc_backptr.h b/gc/include/gc_backptr.h
new file mode 100644
index 0000000..5899496
--- /dev/null
+++ b/gc/include/gc_backptr.h
@@ -0,0 +1,65 @@
+/*
+ * This is a simple API to implement pointer back tracing, i.e.
+ * to answer questions such as "who is pointing to this" or
+ * "why is this object being retained by the collector"
+ *
+ * This API assumes that we have an ANSI C compiler.
+ *
+ * Most of these calls yield useful information on only after
+ * a garbage collection.  Usually the client will first force
+ * a full collection and then gather information, preferably
+ * before much intervening allocation.
+ *
+ * The implementation of the interface is only about 99.9999%
+ * correct.  It is intended to be good enough for profiling,
+ * but is not intended to be used with production code.
+ *
+ * Results are likely to be much more useful if all allocation is
+ * accomplished through the debugging allocators.
+ *
+ * The implementation idea is due to A. Demers.
+ */
+
+#ifndef GC_BACKPTR_H
+#define GC_BACKPTR_H
+/* Store information about the object referencing dest in *base_p     */
+/* and *offset_p.                                                     */
+/* If multiple objects or roots point to dest, the one reported	      */
+/* will be the last on used by the garbage collector to trace the     */
+/* object.							      */
+/*   source is root ==> *base_p = address, *offset_p = 0	      */
+/*   source is heap object ==> *base_p != 0, *offset_p = offset       */
+/*   Returns 1 on success, 0 if source couldn't be determined.        */
+/* Dest can be any address within a heap object.                      */
+typedef enum {  GC_UNREFERENCED, /* No reference info available.	*/
+		GC_NO_SPACE,	/* Dest not allocated with debug alloc  */
+		GC_REFD_FROM_ROOT, /* Referenced directly by root *base_p */
+		GC_REFD_FROM_REG,  /* Referenced from a register, i.e.	*/
+				   /* a root without an address.	*/
+		GC_REFD_FROM_HEAP, /* Referenced from another heap obj. */
+		GC_FINALIZER_REFD /* Finalizable and hence accessible.  */
+} GC_ref_kind;
+
+GC_ref_kind GC_get_back_ptr_info(void *dest, void **base_p, size_t *offset_p);
+
+/* Generate a random heap address.            */
+/* The resulting address is in the heap, but  */
+/* not necessarily inside a valid object.     */
+void * GC_generate_random_heap_address(void);
+
+/* Generate a random address inside a valid marked heap object. */
+void * GC_generate_random_valid_address(void);
+
+/* Force a garbage collection and generate a backtrace from a */
+/* random heap address.                                       */
+/* This uses the GC logging mechanism (GC_printf) to produce  */
+/* output.  It can often be called from a debugger.  The      */
+/* source in dbg_mlc.c also serves as a sample client.	      */
+void GC_generate_random_backtrace(void);
+
+/* Print a backtrace from a specific address.  Used by the 	*/
+/* above.  The client should call GC_gcollect() immediately	*/
+/* before invocation.						*/
+void GC_print_backtrace(void *);
+
+#endif /* GC_BACKPTR_H */