boehm-gc/backptr.h

   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 /* Store information about the object referencing dest in *base_p     */
  24 /* and *offset_p.                                                     */
  25 /* If multiple objects or roots point to dest, the one reported       */
  26 /* will be the last on used by the garbage collector to trace the     */
  27 /* object.                                                            */
  28 /*   source is root ==> *base_p = address, *offset_p = 0              */
  29 /*   source is heap object ==> *base_p != 0, *offset_p = offset       */
  30 /*   Returns 1 on success, 0 if source couldn't be determined.        */
  31 /* Dest can be any address within a heap object.                      */
  32 typedef enum {  GC_UNREFERENCED, /* No reference info available.        */
  33                 GC_NO_SPACE,    /* Dest not allocated with debug alloc  */
  34                 GC_REFD_FROM_ROOT, /* Referenced directly by root *base_p */
  35                 GC_REFD_FROM_REG,  /* Referenced from a register, i.e.  */
  36                                    /* a root without an address.        */
  37                 GC_REFD_FROM_HEAP, /* Referenced from another heap obj. */
  38                 GC_FINALIZER_REFD /* Finalizable and hence accessible.  */
  39 } GC_ref_kind;
  40
  41 GC_ref_kind GC_get_back_ptr_info(void *dest, void **base_p, size_t *offset_p);
  42
  43 /* Generate a random heap address.            */
  44 /* The resulting address is in the heap, but  */
  45 /* not necessarily inside a valid object.     */
  46 void * GC_generate_random_heap_address(void);
  47
  48 /* Generate a random address inside a valid marked heap object. */
  49 void * GC_generate_random_valid_address(void);
  50
  51 /* Force a garbage collection and generate a backtrace from a */
  52 /* random heap address.                                       */
  53 /* This uses the GC logging mechanism (GC_printf) to produce  */
  54 /* output.  It can often be called from a debugger.  The      */
  55 /* source in dbg_mlc.c also serves as a sample client.        */
  56 void GC_generate_random_backtrace(void);
  57
  58 /* Print a backtrace from a specific address.  Used by the      */
  59 /* above.  The client should call GC_gcollect() immediately     */
  60 /* before invocation.                                           */
  61 void GC_print_backtrace(void *);
  62
  63