+++ /dev/null
-/*
- * Copyright (c) 2001 by Hewlett-Packard Company. All rights reserved.
- *
- * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
- * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
- *
- * Permission is hereby granted to use or copy this program
- * for any purpose, provided the above notices are retained on all copies.
- * Permission to modify the code and to distribute modified code is granted,
- * provided the above notices are retained, and a notice that the code was
- * modified is included with the above copyright notice.
- *
- */
-
-/*
- * This implements a full, though not well-tuned, representation of the
- * backwards points-to graph. This is used to test for non-GC-robust
- * data structures; the code is not used during normal garbage collection.
- *
- * One restriction is that we drop all back-edges from nodes with very
- * high in-degree, and simply add them add them to a list of such
- * nodes. They are then treated as permanent roots. Id this by itself
- * doesn't introduce a space leak, then such nodes can't contribute to
- * a growing space leak.
- */
-
-#ifdef MAKE_BACK_GRAPH
-
-#define MAX_IN 10 /* Maximum in-degree we handle directly */
-
-#include "private/dbg_mlc.h"
-#include <unistd.h>
-
-#if !defined(DBG_HDRS_ALL) || (ALIGNMENT != CPP_WORDSZ/8) || !defined(UNIX_LIKE)
-# error Configuration doesnt support MAKE_BACK_GRAPH
-#endif
-
-/* We store single back pointers directly in the object's oh_bg_ptr field. */
-/* If there is more than one ptr to an object, we store q | FLAG_MANY, */
-/* where q is a pointer to a back_edges object. */
-/* Every once in a while we use a back_edges object even for a single */
-/* pointer, since we need the other fields in the back_edges structure to */
-/* be present in some fraction of the objects. Otherwise we get serious */
-/* performance issues. */
-#define FLAG_MANY 2
-
-typedef struct back_edges_struct {
- word n_edges; /* Number of edges, including those in continuation */
- /* structures. */
- unsigned short flags;
-# define RETAIN 1 /* Directly points to a reachable object; */
- /* retain for next GC. */
- unsigned short height_gc_no;
- /* If height > 0, then the GC_gc_no value when it */
- /* was computed. If it was computed this cycle, then */
- /* it is current. If it was computed during the */
- /* last cycle, then it represents the old height, */
- /* which is only saved for live objects referenced by */
- /* dead ones. This may grow due to refs from newly */
- /* dead objects. */
- signed_word height;
- /* Longest path through unreachable nodes to this node */
- /* that we found using depth first search. */
-
-# define HEIGHT_UNKNOWN ((signed_word)(-2))
-# define HEIGHT_IN_PROGRESS ((signed_word)(-1))
- ptr_t edges[MAX_IN];
- struct back_edges_struct *cont;
- /* Pointer to continuation structure; we use only the */
- /* edges field in the continuation. */
- /* also used as free list link. */
-} back_edges;
-
-/* Allocate a new back edge structure. Should be more sophisticated */
-/* if this were production code. */
-#define MAX_BACK_EDGE_STRUCTS 100000
-static back_edges *back_edge_space = 0;
-int GC_n_back_edge_structs = 0; /* Serves as pointer to never used */
- /* back_edges space. */
-static back_edges *avail_back_edges = 0;
- /* Pointer to free list of deallocated */
- /* back_edges structures. */
-
-static back_edges * new_back_edges(void)
-{
- if (0 == back_edge_space) {
- back_edge_space = (back_edges *)
- sbrk(MAX_BACK_EDGE_STRUCTS*sizeof(back_edges));
- }
- if (0 != avail_back_edges) {
- back_edges * result = avail_back_edges;
- avail_back_edges = result -> cont;
- result -> cont = 0;
- return result;
- }
- if (GC_n_back_edge_structs >= MAX_BACK_EDGE_STRUCTS - 1) {
- ABORT("needed too much space for back edges: adjust "
- "MAX_BACK_EDGE_STRUCTS");
- }
- return back_edge_space + (GC_n_back_edge_structs++);
-}
-
-/* Deallocate p and its associated continuation structures. */
-static void deallocate_back_edges(back_edges *p)
-{
- back_edges *last = p;
-
- while (0 != last -> cont) last = last -> cont;
- last -> cont = avail_back_edges;
- avail_back_edges = p;
-}
-
-/* Table of objects that are currently on the depth-first search */
-/* stack. Only objects with in-degree one are in this table. */
-/* Other objects are identified using HEIGHT_IN_PROGRESS. */
-/* This data structure NEEDS IMPROVEMENT. */
-#define MAX_IN_PROGRESS 10000
-static ptr_t * in_progress_space = 0;
-static int n_in_progress = 0;
-
-static void push_in_progress(ptr_t p)
-{
- if (in_progress_space == 0)
- in_progress_space = sbrk(MAX_IN_PROGRESS * sizeof(ptr_t));
- if (n_in_progress == MAX_IN_PROGRESS)
- ABORT("Exceeded MAX_IN_PROGRESS");
- in_progress_space[n_in_progress++] = p;
-}
-
-static GC_bool is_in_progress(ptr_t p)
-{
- int i;
- for (i = 0; i < n_in_progress; ++i) {
- if (in_progress_space[i] == p) return TRUE;
- }
- return FALSE;
-}
-
-static void pop_in_progress(ptr_t p)
-{
- --n_in_progress;
- GC_ASSERT(in_progress_space[n_in_progress] == p);
-}
-
-#define GET_OH_BG_PTR(p) \
- (ptr_t)REVEAL_POINTER(((oh *)(p)) -> oh_bg_ptr)
-#define SET_OH_BG_PTR(p,q) (((oh *)(p)) -> oh_bg_ptr) = HIDE_POINTER(q)
-
-/* Execute s once for each predecessor q of p in the points-to graph. */
-/* s should be a bracketed statement. We declare q. */
-#define FOR_EACH_PRED(q, p, s) \
- { \
- ptr_t q = GET_OH_BG_PTR(p); \
- if (!((word)q & FLAG_MANY)) { \
- if (q && !((word)q & 1)) s \
- /* !((word)q & 1) checks for a misnterpreted freelist link */ \
- } else { \
- back_edges *orig_be_ = (back_edges *)((word)q & ~FLAG_MANY); \
- back_edges *be_ = orig_be_; \
- int total_, local_; \
- int n_edges_ = be_ -> n_edges; \
- for (total_ = 0, local_ = 0; total_ < n_edges_; ++local_, ++total_) { \
- if (local_ == MAX_IN) { \
- be_ = be_ -> cont; \
- local_ = 0; \
- } \
- q = be_ -> edges[local_]; s \
- } \
- } \
- }
-
-/* Ensure that p has a back_edges structure associated with it. */
-static void ensure_struct(ptr_t p)
-{
- ptr_t old_back_ptr = GET_OH_BG_PTR(p);
-
- if (!((word)old_back_ptr & FLAG_MANY)) {
- back_edges *be = new_back_edges();
- be -> flags = 0;
- if (0 == old_back_ptr) {
- be -> n_edges = 0;
- } else {
- be -> n_edges = 1;
- be -> edges[0] = old_back_ptr;
- }
- be -> height = HEIGHT_UNKNOWN;
- be -> height_gc_no = GC_gc_no - 1;
- GC_ASSERT(be >= back_edge_space);
- SET_OH_BG_PTR(p, (word)be | FLAG_MANY);
- }
-}
-
-/* Add the (forward) edge from p to q to the backward graph. Both p */
-/* q are pointers to the object base, i.e. pointers to an oh. */
-static void add_edge(ptr_t p, ptr_t q)
-{
- ptr_t old_back_ptr = GET_OH_BG_PTR(q);
- back_edges * be, *be_cont;
- word i;
- static unsigned random_number = 13;
-# define GOT_LUCKY_NUMBER (((++random_number) & 0x7f) == 0)
- /* A not very random number we use to occasionally allocate a */
- /* back_edges structure even for a single backward edge. This */
- /* prevents us from repeatedly tracing back through very long */
- /* chains, since we will have some place to store height and */
- /* in_progress flags along the way. */
-
- GC_ASSERT(p == GC_base(p) && q == GC_base(q));
- if (!GC_HAS_DEBUG_INFO(q) || !GC_HAS_DEBUG_INFO(p)) {
- /* This is really a misinterpreted free list link, since we saw */
- /* a pointer to a free list. Dont overwrite it! */
- return;
- }
- if (0 == old_back_ptr) {
- SET_OH_BG_PTR(q, p);
- if (GOT_LUCKY_NUMBER) ensure_struct(q);
- return;
- }
- /* Check whether it was already in the list of predecessors. */
- FOR_EACH_PRED(pred, q, { if (p == pred) return; });
- ensure_struct(q);
- old_back_ptr = GET_OH_BG_PTR(q);
- be = (back_edges *)((word)old_back_ptr & ~FLAG_MANY);
- for (i = be -> n_edges, be_cont = be; i > MAX_IN;
- be_cont = be_cont -> cont, i -= MAX_IN) {}
- if (i == MAX_IN) {
- be_cont -> cont = new_back_edges();
- be_cont = be_cont -> cont;
- i = 0;
- }
- be_cont -> edges[i] = p;
- be -> n_edges++;
- if (be -> n_edges == 100) {
-# if 0
- if (GC_print_stats) {
- GC_err_printf0("The following object has in-degree >= 100:\n");
- GC_print_heap_obj(q);
- }
-# endif
- }
-}
-
-typedef void (*per_object_func)(ptr_t p, word n_words, word gc_descr);
-
-static void per_object_helper(struct hblk *h, word fn)
-{
- hdr * hhdr = HDR(h);
- word sz = hhdr -> hb_sz;
- word descr = hhdr -> hb_descr;
- per_object_func f = (per_object_func)fn;
- int i = 0;
-
- do {
- f((ptr_t)(h -> hb_body + i), sz, descr);
- i += sz;
- } while (i + sz <= BYTES_TO_WORDS(HBLKSIZE));
-}
-
-void GC_apply_to_each_object(per_object_func f)
-{
- GC_apply_to_all_blocks(per_object_helper, (word)f);
-}
-
-static void reset_back_edge(ptr_t p, word n_words, word gc_descr)
-{
- /* Skip any free list links, or dropped blocks */
- if (GC_HAS_DEBUG_INFO(p)) {
- ptr_t old_back_ptr = GET_OH_BG_PTR(p);
- if ((word)old_back_ptr & FLAG_MANY) {
- back_edges *be = (back_edges *)((word)old_back_ptr & ~FLAG_MANY);
- if (!(be -> flags & RETAIN)) {
- deallocate_back_edges(be);
- SET_OH_BG_PTR(p, 0);
- } else {
- word *currentp;
-
- GC_ASSERT(GC_is_marked(p));
-
- /* Back edges may point to objects that will not be retained. */
- /* Delete them for now, but remember the height. */
- /* Some will be added back at next GC. */
- be -> n_edges = 0;
- if (0 != be -> cont) {
- deallocate_back_edges(be -> cont);
- be -> cont = 0;
- }
-
- GC_ASSERT(GC_is_marked(p));
-
- /* We only retain things for one GC cycle at a time. */
- be -> flags &= ~RETAIN;
- }
- } else /* Simple back pointer */ {
- /* Clear to avoid dangling pointer. */
- SET_OH_BG_PTR(p, 0);
- }
- }
-}
-
-static void add_back_edges(ptr_t p, word n_words, word gc_descr)
-{
- word *currentp = (word *)(p + sizeof(oh));
-
- /* For now, fix up non-length descriptors conservatively. */
- if((gc_descr & GC_DS_TAGS) != GC_DS_LENGTH) {
- gc_descr = WORDS_TO_BYTES(n_words);
- }
- while (currentp < (word *)(p + gc_descr)) {
- word current = *currentp++;
- if (current >= (word)GC_least_plausible_heap_addr &&
- current <= (word)GC_greatest_plausible_heap_addr) {
- ptr_t target = GC_base((GC_PTR)current);
- if (0 != target) {
- add_edge(p, target);
- }
- }
- }
-}
-
-/* Rebuild the reprentation of the backward reachability graph. */
-/* Does not examine mark bits. Can be called before GC. */
-void GC_build_back_graph(void)
-{
- GC_apply_to_each_object(add_back_edges);
-}
-
-/* Return an approximation to the length of the longest simple path */
-/* through unreachable objects to p. We refer to this as the height */
-/* of p. */
-static word backwards_height(ptr_t p)
-{
- word result;
- ptr_t back_ptr = GET_OH_BG_PTR(p);
- back_edges *be;
-
- if (0 == back_ptr) return 1;
- if (!((word)back_ptr & FLAG_MANY)) {
- if (is_in_progress(p)) return 0; /* DFS back edge, i.e. we followed */
- /* an edge to an object already */
- /* on our stack: ignore */
- push_in_progress(p);
- result = backwards_height(back_ptr)+1;
- pop_in_progress(p);
- return result;
- }
- be = (back_edges *)((word)back_ptr & ~FLAG_MANY);
- if (be -> height >= 0 && be -> height_gc_no == GC_gc_no)
- return be -> height;
- /* Ignore back edges in DFS */
- if (be -> height == HEIGHT_IN_PROGRESS) return 0;
- result = (be -> height > 0? be -> height : 1);
- be -> height = HEIGHT_IN_PROGRESS;
- FOR_EACH_PRED(q, p, {
- word this_height;
- if (GC_is_marked(q) && !(FLAG_MANY & (word)GET_OH_BG_PTR(p))) {
- if (GC_print_stats)
- GC_printf2("Found bogus pointer from 0x%lx to 0x%lx\n", q, p);
- /* Reachable object "points to" unreachable one. */
- /* Could be caused by our lax treatment of GC descriptors. */
- this_height = 1;
- } else {
- this_height = backwards_height(q);
- }
- if (this_height >= result) result = this_height + 1;
- });
- be -> height = result;
- be -> height_gc_no = GC_gc_no;
- return result;
-}
-
-word GC_max_height;
-ptr_t GC_deepest_obj;
-
-/* Compute the maximum height of every unreachable predecessor p of a */
-/* reachable object. Arrange to save the heights of all such objects p */
-/* so that they can be used in calculating the height of objects in the */
-/* next GC. */
-/* Set GC_max_height to be the maximum height we encounter, and */
-/* GC_deepest_obj to be the corresponding object. */
-static void update_max_height(ptr_t p, word n_words, word gc_descr)
-{
- if (GC_is_marked(p) && GC_HAS_DEBUG_INFO(p)) {
- int i;
- word p_height = 0;
- ptr_t p_deepest_obj = 0;
- ptr_t back_ptr;
- back_edges *be = 0;
-
- /* If we remembered a height last time, use it as a minimum. */
- /* It may have increased due to newly unreachable chains pointing */
- /* to p, but it can't have decreased. */
- back_ptr = GET_OH_BG_PTR(p);
- if (0 != back_ptr && ((word)back_ptr & FLAG_MANY)) {
- be = (back_edges *)((word)back_ptr & ~FLAG_MANY);
- if (be -> height != HEIGHT_UNKNOWN) p_height = be -> height;
- }
- FOR_EACH_PRED(q, p, {
- if (!GC_is_marked(q) && GC_HAS_DEBUG_INFO(q)) {
- word q_height;
-
- q_height = backwards_height(q);
- if (q_height > p_height) {
- p_height = q_height;
- p_deepest_obj = q;
- }
- }
- });
- if (p_height > 0) {
- /* Remember the height for next time. */
- if (be == 0) {
- ensure_struct(p);
- back_ptr = GET_OH_BG_PTR(p);
- be = (back_edges *)((word)back_ptr & ~FLAG_MANY);
- }
- be -> flags |= RETAIN;
- be -> height = p_height;
- be -> height_gc_no = GC_gc_no;
- }
- if (p_height > GC_max_height) {
- GC_max_height = p_height;
- GC_deepest_obj = p_deepest_obj;
- }
- }
-}
-
-void GC_traverse_back_graph(void)
-{
- static word max_max_height = 0;
- GC_max_height = 0;
- GC_apply_to_each_object(update_max_height);
- GC_printf2("Maximum backwards height of reachable objects at GC %lu is %ld\n",
- (unsigned long) GC_gc_no, GC_max_height);
- if (GC_max_height > max_max_height) {
- max_max_height = GC_max_height;
- GC_printf0("The following unreachable object is last in a longest chain "
- "of unreachable objects:\n");
- GC_print_heap_obj(GC_deepest_obj);
- }
- if (GC_print_stats) {
- GC_printf1("Needed max total of %ld back-edge structs\n",
- GC_n_back_edge_structs);
- }
- GC_apply_to_each_object(reset_back_edge);
- GC_deepest_obj = 0;
-}
-
-#endif /* MAKE_BACK_GRAPH */
projects / msp430-gcc.git / blobdiff