1 /* 2 * This is a simple API to implement pointer back tracing, i.e. 3 * to answer questions such as "who is pointing to this" or 4 * "why is this object being retained by the collector" 5 * 6 * This API assumes that we have an ANSI C compiler. 7 * 8 * Most of these calls yield useful information on only after 9 * a garbage collection. Usually the client will first force 10 * a full collection and then gather information, preferably 11 * before much intervening allocation. 12 * 13 * The implementation of the interface is only about 99.9999% 14 * correct. It is intended to be good enough for profiling, 15 * but is not intended to be used with production code. 16 * 17 * Results are likely to be much more useful if all allocation is 18 * accomplished through the debugging allocators. 19 * 20 * The implementation idea is due to A. Demers. 21 */ 22 23 #ifndef GC_BACKPTR_H 24 #define GC_BACKPTR_H 25 /* Store information about the object referencing dest in *base_p */ 26 /* and *offset_p. */ 27 /* If multiple objects or roots point to dest, the one reported */ 28 /* will be the last on used by the garbage collector to trace the */ 29 /* object. */ 30 /* source is root ==> *base_p = address, *offset_p = 0 */ 31 /* source is heap object ==> *base_p != 0, *offset_p = offset */ 32 /* Returns 1 on success, 0 if source couldn't be determined. */ 33 /* Dest can be any address within a heap object. */ 34 typedef enum { GC_UNREFERENCED, /* No reference info available. */ 35 GC_NO_SPACE, /* Dest not allocated with debug alloc */ 36 GC_REFD_FROM_ROOT, /* Referenced directly by root *base_p */ 37 GC_REFD_FROM_REG, /* Referenced from a register, i.e. */ 38 /* a root without an address. */ 39 GC_REFD_FROM_HEAP, /* Referenced from another heap obj. */ 40 GC_FINALIZER_REFD /* Finalizable and hence accessible. */ 41 } GC_ref_kind; 42 43 GC_ref_kind GC_get_back_ptr_info(void *dest, void **base_p, size_t *offset_p); 44 45 /* Generate a random heap address. */ 46 /* The resulting address is in the heap, but */ 47 /* not necessarily inside a valid object. */ 48 void * GC_generate_random_heap_address(void); 49 50 /* Generate a random address inside a valid marked heap object. */ 51 void * GC_generate_random_valid_address(void); 52 53 /* Force a garbage collection and generate a backtrace from a */ 54 /* random heap address. */ 55 /* This uses the GC logging mechanism (GC_printf) to produce */ 56 /* output. It can often be called from a debugger. The */ 57 /* source in dbg_mlc.c also serves as a sample client. */ 58 void GC_generate_random_backtrace(void); 59 60 /* Print a backtrace from a specific address. Used by the */ 61 /* above. The client should call GC_gcollect() immediately */ 62 /* before invocation. */ 63 void GC_print_backtrace(void *); 64 65 #endif /* GC_BACKPTR_H */ 66