1 /*
  2  * Copyright (c) 2019, 2021, 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 "logging/log.hpp"
 27 #include "logging/logStream.hpp"
 28 #include "memory/memRegion.hpp"
 29 #include "memory/resourceArea.hpp"
 30 #include "memory/universe.hpp"
 31 #include "memory/virtualspace.hpp"
 32 #include "oops/compressedOops.hpp"
 33 #include "gc/shared/collectedHeap.hpp"
 34 #include "runtime/arguments.hpp"
 35 #include "runtime/globals.hpp"
 36 
 37 // For UseCompressedOops.
 38 NarrowPtrStruct CompressedOops::_narrow_oop = { NULL, 0, true };
 39 MemRegion       CompressedOops::_heap_address_range;
 40 
 41 // Choose the heap base address and oop encoding mode
 42 // when compressed oops are used:
 43 // Unscaled  - Use 32-bits oops without encoding when
 44 //     NarrowOopHeapBaseMin + heap_size < 4Gb
 45 // ZeroBased - Use zero based compressed oops with encoding when
 46 //     NarrowOopHeapBaseMin + heap_size < 32Gb
 47 // HeapBased - Use compressed oops with heap base + encoding.
 48 void CompressedOops::initialize(const ReservedHeapSpace& heap_space) {
 49 #ifdef _LP64
 50   // Subtract a page because something can get allocated at heap base.
 51   // This also makes implicit null checking work, because the
 52   // memory+1 page below heap_base needs to cause a signal.
 53   // See needs_explicit_null_check.
 54   // Only set the heap base for compressed oops because it indicates
 55   // compressed oops for pstack code.
 56   if ((uint64_t)heap_space.end() > UnscaledOopHeapMax) {
 57     // Didn't reserve heap below 4Gb.  Must shift.
 58     set_shift(LogMinObjAlignmentInBytes);
 59   }
 60   if ((uint64_t)heap_space.end() <= OopEncodingHeapMax) {
 61     // Did reserve heap below 32Gb. Can use base == 0;
 62     set_base(0);
 63   } else {
 64     set_base((address)heap_space.compressed_oop_base());
 65   }
 66 
 67   _heap_address_range = heap_space.region();
 68 
 69   LogTarget(Debug, gc, heap, coops) lt;
 70   if (lt.is_enabled()) {
 71     ResourceMark rm;
 72     LogStream ls(lt);
 73     print_mode(&ls);
 74   }
 75 
 76   // Tell tests in which mode we run.
 77   Arguments::PropertyList_add(new SystemProperty("java.vm.compressedOopsMode",
 78                                                  mode_to_string(mode()),
 79                                                  false));
 80 
 81   // base() is one page below the heap.
 82   assert((intptr_t)base() <= ((intptr_t)_heap_address_range.start() - os::vm_page_size()) ||
 83          base() == NULL, "invalid value");
 84   assert(shift() == LogMinObjAlignmentInBytes ||
 85          shift() == 0, "invalid value");
 86 #endif
 87 }
 88 
 89 void CompressedOops::set_base(address base) {
 90   assert(UseCompressedOops, "no compressed oops?");
 91   _narrow_oop._base    = base;
 92 }
 93 
 94 void CompressedOops::set_shift(int shift) {
 95   _narrow_oop._shift   = shift;
 96 }
 97 
 98 void CompressedOops::set_use_implicit_null_checks(bool use) {
 99   assert(UseCompressedOops, "no compressed ptrs?");
100   _narrow_oop._use_implicit_null_checks   = use;
101 }
102 
103 bool CompressedOops::is_in(void* addr) {
104   return _heap_address_range.contains(addr);
105 }
106 
107 bool CompressedOops::is_in(MemRegion mr) {
108   return _heap_address_range.contains(mr);
109 }
110 
111 CompressedOops::Mode CompressedOops::mode() {
112   if (base_disjoint()) {
113     return DisjointBaseNarrowOop;
114   }
115 
116   if (base() != 0) {
117     return HeapBasedNarrowOop;
118   }
119 
120   if (shift() != 0) {
121     return ZeroBasedNarrowOop;
122   }
123 
124   return UnscaledNarrowOop;
125 }
126 
127 const char* CompressedOops::mode_to_string(Mode mode) {
128   switch (mode) {
129     case UnscaledNarrowOop:
130       return "32-bit";
131     case ZeroBasedNarrowOop:
132       return "Zero based";
133     case DisjointBaseNarrowOop:
134       return "Non-zero disjoint base";
135     case HeapBasedNarrowOop:
136       return "Non-zero based";
137     default:
138       ShouldNotReachHere();
139       return "";
140   }
141 }
142 
143 // Test whether bits of addr and possible offsets into the heap overlap.
144 bool CompressedOops::is_disjoint_heap_base_address(address addr) {
145   return (((uint64_t)(intptr_t)addr) &
146           (((uint64_t)UCONST64(0xFFFFffffFFFFffff)) >> (32-LogMinObjAlignmentInBytes))) == 0;
147 }
148 
149 // Check for disjoint base compressed oops.
150 bool CompressedOops::base_disjoint() {
151   return _narrow_oop._base != NULL && is_disjoint_heap_base_address(_narrow_oop._base);
152 }
153 
154 // Check for real heapbased compressed oops.
155 // We must subtract the base as the bits overlap.
156 // If we negate above function, we also get unscaled and zerobased.
157 bool CompressedOops::base_overlaps() {
158   return _narrow_oop._base != NULL && !is_disjoint_heap_base_address(_narrow_oop._base);
159 }
160 
161 void CompressedOops::print_mode(outputStream* st) {
162   st->print("Heap address: " PTR_FORMAT ", size: " SIZE_FORMAT " MB",
163             p2i(_heap_address_range.start()), _heap_address_range.byte_size()/M);
164 
165   st->print(", Compressed Oops mode: %s", mode_to_string(mode()));
166 
167   if (base() != 0) {
168     st->print(": " PTR_FORMAT, p2i(base()));
169   }
170 
171   if (shift() != 0) {
172     st->print(", Oop shift amount: %d", shift());
173   }
174 
175   if (!use_implicit_null_checks()) {
176     st->print(", no protected page in front of the heap");
177   }
178   st->cr();
179 }