rev 55196 : 8225716: G1 GC: Undefined behaviour in G1BlockOffsetTablePart::block_at_or_preceding
Reviewed-by: duke

   1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
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  24 
  25 #ifndef SHARE_GC_G1_G1BLOCKOFFSETTABLE_INLINE_HPP
  26 #define SHARE_GC_G1_G1BLOCKOFFSETTABLE_INLINE_HPP
  27 
  28 #include "gc/g1/g1BlockOffsetTable.hpp"
  29 #include "gc/g1/heapRegion.hpp"
  30 #include "gc/shared/memset_with_concurrent_readers.hpp"
  31 #include "gc/shared/space.hpp"
  32 
  33 inline HeapWord* G1BlockOffsetTablePart::block_start(const void* addr) {
  34   if (addr >= _space->bottom() && addr < _space->end()) {
  35     HeapWord* q = block_at_or_preceding(addr, true, _next_offset_index-1);
  36     return forward_to_block_containing_addr(q, addr);
  37   } else {
  38     return NULL;
  39   }
  40 }
  41 
  42 inline HeapWord* G1BlockOffsetTablePart::block_start_const(const void* addr) const {
  43   if (addr >= _space->bottom() && addr < _space->end()) {
  44     HeapWord* q = block_at_or_preceding(addr, true, _next_offset_index-1);
  45     HeapWord* n = q + block_size(q);
  46     return forward_to_block_containing_addr_const(q, n, addr);
  47   } else {
  48     return NULL;
  49   }
  50 }
  51 
  52 u_char G1BlockOffsetTable::offset_array(size_t index) const {
  53   check_index(index, "index out of range");
  54   return _offset_array[index];
  55 }
  56 
  57 void G1BlockOffsetTable::set_offset_array(size_t index, u_char offset) {
  58   check_index(index, "index out of range");
  59   set_offset_array_raw(index, offset);
  60 }
  61 
  62 void G1BlockOffsetTable::set_offset_array(size_t index, HeapWord* high, HeapWord* low) {
  63   check_index(index, "index out of range");
  64   assert(high >= low, "addresses out of order");
  65   size_t offset = pointer_delta(high, low);
  66   check_offset(offset, "offset too large");
  67   set_offset_array(index, (u_char)offset);
  68 }
  69 
  70 void G1BlockOffsetTable::set_offset_array(size_t left, size_t right, u_char offset) {
  71   check_index(right, "right index out of range");
  72   assert(left <= right, "indexes out of order");
  73   size_t num_cards = right - left + 1;
  74   memset_with_concurrent_readers(&_offset_array[left], offset, num_cards);
  75 }
  76 
  77 // Variant of index_for that does not check the index for validity.
  78 inline size_t G1BlockOffsetTable::index_for_raw(const void* p) const {
  79   return pointer_delta((char*)p, _reserved.start(), sizeof(char)) >> BOTConstants::LogN;
  80 }
  81 
  82 inline size_t G1BlockOffsetTable::index_for(const void* p) const {
  83   char* pc = (char*)p;
  84   assert(pc >= (char*)_reserved.start() &&
  85          pc <  (char*)_reserved.end(),
  86          "p (" PTR_FORMAT ") not in reserved [" PTR_FORMAT ", " PTR_FORMAT ")",
  87          p2i(p), p2i(_reserved.start()), p2i(_reserved.end()));
  88   size_t result = index_for_raw(p);
  89   check_index(result, "bad index from address");
  90   return result;
  91 }
  92 
  93 inline HeapWord* G1BlockOffsetTable::address_for_index(size_t index) const {
  94   check_index(index, "index out of range");
  95   HeapWord* result = address_for_index_raw(index);
  96   assert(result >= _reserved.start() && result < _reserved.end(),
  97          "bad address from index result " PTR_FORMAT
  98          " _reserved.start() " PTR_FORMAT " _reserved.end() " PTR_FORMAT,
  99          p2i(result), p2i(_reserved.start()), p2i(_reserved.end()));
 100   return result;
 101 }
 102 
 103 inline size_t G1BlockOffsetTablePart::block_size(const HeapWord* p) const {
 104   return _space->block_size(p);
 105 }
 106 
 107 inline HeapWord* G1BlockOffsetTablePart::block_at_or_preceding(const void* addr,
 108                                                                bool has_max_index,
 109                                                                size_t max_index) const {
 110   assert(_object_can_span || _bot->offset_array(_bot->index_for(_space->bottom())) == 0,
 111          "Object crossed region boundary, found offset %u instead of 0",
 112          (uint) _bot->offset_array(_bot->index_for(_space->bottom())));
 113   size_t index = _bot->index_for(addr);
 114   // We must make sure that the offset table entry we use is valid.  If
 115   // "addr" is past the end, start at the last known one and go forward.
 116   if (has_max_index) {
 117     index = MIN2(index, max_index);
 118   }
 119   HeapWord* q = _bot->address_for_index(index);
 120 
 121   uint offset = _bot->offset_array(index);  // Extend u_char to uint.
 122   while (offset >= BOTConstants::N_words) {
 123     // The excess of the offset from N_words indicates a power of Base
 124     // to go back by.
 125     size_t n_cards_back = BOTConstants::entry_to_cards_back(offset);
 126     q -= (BOTConstants::N_words * n_cards_back);
 127     index -= n_cards_back;
 128     offset = _bot->offset_array(index);
 129   }
 130   assert(offset < BOTConstants::N_words, "offset too large");
 131   q -= offset;
 132   return q;
 133 }
 134 
 135 inline HeapWord* G1BlockOffsetTablePart::forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
 136                                                                                 const void* addr) const {
 137   if (addr >= _space->top()) return _space->top();
 138   while (n <= addr) {
 139     q = n;
 140     oop obj = oop(q);
 141     if (obj->klass_or_null_acquire() == NULL) {
 142       return q;
 143     }
 144     n += block_size(q);
 145   }
 146   assert(q <= n, "wrong order for q and addr");
 147   assert(addr < n, "wrong order for addr and n");
 148   return q;
 149 }
 150 
 151 inline HeapWord* G1BlockOffsetTablePart::forward_to_block_containing_addr(HeapWord* q,
 152                                                                           const void* addr) {
 153   if (oop(q)->klass_or_null_acquire() == NULL) {
 154     return q;
 155   }
 156   HeapWord* n = q + block_size(q);
 157   // In the normal case, where the query "addr" is a card boundary, and the
 158   // offset table chunks are the same size as cards, the block starting at
 159   // "q" will contain addr, so the test below will fail, and we'll fall
 160   // through quickly.
 161   if (n <= addr) {
 162     q = forward_to_block_containing_addr_slow(q, n, addr);
 163   }
 164   assert(q <= addr, "wrong order for current and arg");
 165   return q;
 166 }
 167 
 168 #endif // SHARE_GC_G1_G1BLOCKOFFSETTABLE_INLINE_HPP
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