1 /*
   2  * Copyright (c) 2002, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "gc/parallel/mutableSpace.hpp"
  27 #include "gc/shared/space.inline.hpp"
  28 #include "gc/shared/spaceDecorator.inline.hpp"
  29 #include "logging/log.hpp"
  30 #include "utilities/copy.hpp"
  31 
  32 // Catch-all file for utility classes
  33 
  34 #ifndef PRODUCT
  35 
  36 // Returns true is the location q matches the mangling
  37 // pattern.
  38 bool SpaceMangler::is_mangled(HeapWord* q) {
  39   // This test loses precision but is good enough
  40   return badHeapWord == (max_juint & reinterpret_cast<uintptr_t>(*q));
  41 }
  42 
  43 
  44 void SpaceMangler::set_top_for_allocations(HeapWord* v)  {
  45   if (v < end()) {
  46     assert(!CheckZapUnusedHeapArea || is_mangled(v),
  47       "The high water mark is not mangled");
  48   }
  49   _top_for_allocations = v;
  50 }
  51 
  52 // Mangle only the unused space that has not previously
  53 // been mangled and that has not been allocated since being
  54 // mangled.
  55 void SpaceMangler::mangle_unused_area() {
  56   assert(ZapUnusedHeapArea, "Mangling should not be in use");
  57   // Mangle between top and the high water mark.  Safeguard
  58   // against the space changing since top_for_allocations was
  59   // set.
  60   HeapWord* mangled_end = MIN2(top_for_allocations(), end());
  61   if (top() < mangled_end) {
  62     MemRegion mangle_mr(top(), mangled_end);
  63     SpaceMangler::mangle_region(mangle_mr);
  64     // Light weight check of mangling.
  65     check_mangled_unused_area(end());
  66   }
  67   // Complete check of unused area which is functional when
  68   // DEBUG_MANGLING is defined.
  69   check_mangled_unused_area_complete();
  70 }
  71 
  72 // A complete mangle is expected in the
  73 // exceptional case where top_for_allocations is not
  74 // properly tracking the high water mark for mangling.
  75 // This can be the case when to-space is being used for
  76 // scratch space during a mark-sweep-compact.  See
  77 // contribute_scratch() and PSMarkSweep::allocate_stacks().
  78 void SpaceMangler::mangle_unused_area_complete() {
  79   assert(ZapUnusedHeapArea, "Mangling should not be in use");
  80   MemRegion mangle_mr(top(), end());
  81   SpaceMangler::mangle_region(mangle_mr);
  82 }
  83 
  84 // Simply mangle the MemRegion mr.
  85 void SpaceMangler::mangle_region(MemRegion mr) {
  86   assert(ZapUnusedHeapArea, "Mangling should not be in use");
  87 #ifdef ASSERT
  88   Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord);
  89 #endif
  90 }
  91 
  92 // Check that top, top_for_allocations and the last
  93 // word of the space are mangled.  In a tight memory
  94 // situation even this light weight mangling could
  95 // cause paging by touching the end of the space.
  96 void  SpaceMangler::check_mangled_unused_area(HeapWord* limit) {
  97   if (CheckZapUnusedHeapArea) {
  98     // This method can be called while the spaces are
  99     // being reshaped so skip the test if the end of the
 100     // space is beyond the specified limit;
 101     if (end() > limit) return;
 102 
 103     assert(top() == end() ||
 104            (is_mangled(top())), "Top not mangled");
 105     assert((top_for_allocations() < top()) ||
 106            (top_for_allocations() >= end()) ||
 107            (is_mangled(top_for_allocations())),
 108            "Older unused not mangled");
 109     assert(top() == end() ||
 110            (is_mangled(end() - 1)), "End not properly mangled");
 111     // Only does checking when DEBUG_MANGLING is defined.
 112     check_mangled_unused_area_complete();
 113   }
 114 }
 115 
 116 #undef DEBUG_MANGLING
 117 // This should only be used while debugging the mangling
 118 // because of the high cost of checking the completeness.
 119 void  SpaceMangler::check_mangled_unused_area_complete() {
 120   if (CheckZapUnusedHeapArea) {
 121     assert(ZapUnusedHeapArea, "Not mangling unused area");
 122 #ifdef DEBUG_MANGLING
 123     HeapWord* q = top();
 124     HeapWord* limit = end();
 125 
 126     bool passed = true;
 127     while (q < limit) {
 128       if (!is_mangled(q)) {
 129         passed = false;
 130         break;
 131       }
 132       q++;
 133     }
 134     assert(passed, "Mangling is not complete");
 135 #endif
 136   }
 137 }
 138 #undef DEBUG_MANGLING
 139 #endif // not PRODUCT