1 /*
2 * Copyright (c) 2019, 2023, 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.
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23 */
24
25 #include "precompiled.hpp"
26 #include "logging/log.hpp"
27 #include "memory/metaspace.hpp"
28 #include "oops/klass.hpp"
29 #include "oops/compressedKlass.inline.hpp"
30 #include "runtime/globals.hpp"
31 #include "runtime/java.hpp"
32 #include "runtime/os.hpp"
33 #include "utilities/debug.hpp"
34 #include "utilities/globalDefinitions.hpp"
35 #include "utilities/ostream.hpp"
36
37 int CompressedKlassPointers::_tiny_cp = -1;
38 int CompressedKlassPointers::_narrow_klass_pointer_bits = -1;
39 int CompressedKlassPointers::_max_shift = -1;
40 #ifdef ASSERT
41 address CompressedKlassPointers::_klass_range_start = (address)-1;
42 address CompressedKlassPointers::_klass_range_end = (address)-1;
43 narrowKlass CompressedKlassPointers::_lowest_valid_narrow_klass_id = (narrowKlass)-1;
44 narrowKlass CompressedKlassPointers::_highest_valid_narrow_klass_id = (narrowKlass)-1;
45 #endif
46
47 address CompressedKlassPointers::_base = (address)-1;
48 int CompressedKlassPointers::_shift = -1;
49 size_t CompressedKlassPointers::_range = (size_t)-1;
50
51 // The maximum allowed length of the Klass range (the address range engulfing
52 // CDS + class space) must not exceed 32-bit.
53 // There is a theoretical limit of: must not exceed the size of a fully-shifted
54 // narrow Klass pointer, which would be 32 + 3 = 35 bits in legacy mode;
55 // however, keeping this size below 32-bit allows us to use decoding techniques
56 // like 16-bit moves into the third quadrant on some architectures, and keeps
57 // the code less complex. 32-bit have always been enough for CDS+class space.
58 static constexpr size_t max_klass_range_size = 4 * G;
59
60 #ifdef _LP64
61
62 void CompressedKlassPointers::pre_initialize() {
63 if (UseCompactObjectHeaders) {
64 _tiny_cp = 1;
65 _narrow_klass_pointer_bits = narrow_klass_pointer_bits_tinycp;
66 _max_shift = max_shift_tinycp;
67 } else {
68 _tiny_cp = 0;
69 _narrow_klass_pointer_bits = narrow_klass_pointer_bits_legacy;
70 _max_shift = max_shift_legacy;
71 }
72 }
73
74 #ifdef ASSERT
75 void CompressedKlassPointers::sanity_check_after_initialization() {
76 // In expectation of an assert, prepare condensed info to be printed with the assert.
77 char tmp[256];
78 os::snprintf(tmp, sizeof(tmp), PTR_FORMAT " " PTR_FORMAT " " PTR_FORMAT " %d " SIZE_FORMAT " %u %u",
79 p2i(_klass_range_start), p2i(_klass_range_end), p2i(_base), _shift, _range,
80 _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id);
81 #define ASSERT_HERE(cond) assert(cond, " (%s)", tmp);
82 #define ASSERT_HERE_2(cond, msg) assert(cond, msg " (%s)", tmp);
83
84 // There is no technical reason preventing us from using other klass pointer bit lengths,
85 // but it should be a deliberate choice
86 ASSERT_HERE(_narrow_klass_pointer_bits == 32 || _narrow_klass_pointer_bits == 22);
87
88 // All values must be inited
89 ASSERT_HERE(_max_shift != -1);
90 ASSERT_HERE(_klass_range_start != (address)-1);
91 ASSERT_HERE(_klass_range_end != (address)-1);
92 ASSERT_HERE(_lowest_valid_narrow_klass_id != (narrowKlass)-1);
93 ASSERT_HERE(_base != (address)-1);
94 ASSERT_HERE(_shift != -1);
95 ASSERT_HERE(_range != (size_t)-1);
96
97 const size_t klab = klass_alignment_in_bytes();
98 ASSERT_HERE(klab >= sizeof(uint64_t) && klab <= K);
99
100 // Check that Klass range is fully engulfed in the encoding range
101 ASSERT_HERE(_klass_range_end > _klass_range_start);
102
103 const address encoding_end = _base + nth_bit(narrow_klass_pointer_bits() + _shift);
104 ASSERT_HERE_2(_klass_range_start >= _base && _klass_range_end <= encoding_end,
105 "Resulting encoding range does not fully cover the class range");
106
107 // Check that Klass range is aligned to Klass alignment. That should never be an issue since we mmap the
108 // relevant regions and klass alignment - tied to smallest metachunk size of 1K - will always be smaller
109 // than smallest page size of 4K.
110 ASSERT_HERE_2(is_aligned(_klass_range_start, klab) && is_aligned(_klass_range_end, klab),
111 "Klass range must start at a properly aligned address");
112
113 // Check that lowest and highest possible narrowKlass values make sense
114 ASSERT_HERE_2(_lowest_valid_narrow_klass_id > 0, "Null is not a valid narrowKlass");
115 ASSERT_HERE(_highest_valid_narrow_klass_id > _lowest_valid_narrow_klass_id);
116
117 Klass* k1 = decode_not_null_without_asserts(_lowest_valid_narrow_klass_id, _base, _shift);
118 ASSERT_HERE_2((address)k1 == _klass_range_start + klab, "Not lowest");
119 narrowKlass nk1 = encode_not_null_without_asserts(k1, _base, _shift);
120 ASSERT_HERE_2(nk1 == _lowest_valid_narrow_klass_id, "not reversible");
121
122 Klass* k2 = decode_not_null_without_asserts(_highest_valid_narrow_klass_id, _base, _shift);
123 // _highest_valid_narrow_klass_id must be decoded to the highest theoretically possible
124 // valid Klass* position in range, if we assume minimal Klass size
125 ASSERT_HERE((address)k2 < _klass_range_end);
126 ASSERT_HERE_2(align_up(((address)k2 + sizeof(Klass)), klab) >= _klass_range_end, "Not highest");
127 narrowKlass nk2 = encode_not_null_without_asserts(k2, _base, _shift);
128 ASSERT_HERE_2(nk2 == _highest_valid_narrow_klass_id, "not reversible");
129
130 #ifdef AARCH64
131 // On aarch64, we never expect a shift value > 0 in legacy mode
132 ASSERT_HERE_2(tiny_classpointer_mode() || _shift == 0, "Shift > 0 in legacy mode?");
133 #endif
134 #undef ASSERT_HERE
135 #undef ASSERT_HERE_2
136 }
137
138 void CompressedKlassPointers::calc_lowest_highest_narrow_klass_id() {
139 // Given a Klass range, calculate lowest and highest narrowKlass.
140 const size_t klab = klass_alignment_in_bytes();
141 // Note that 0 is not a valid narrowKlass, and Metaspace prevents us for that reason from allocating at
142 // the very start of class space. So the very first valid Klass position is start-of-range + klab.
143 _lowest_valid_narrow_klass_id =
144 (narrowKlass) (((uintptr_t)(_klass_range_start - _base) + klab) >> _shift);
145 address highest_possible_klass = align_down(_klass_range_end - sizeof(Klass), klab);
146 _highest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(highest_possible_klass - _base) >> _shift);
147 }
148 #endif // ASSERT
149
150 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
151 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
152 // archived heap objects.
153 void CompressedKlassPointers::initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift) {
154 address const end = addr + len;
155
156 if (len > max_klass_range_size) {
157 // Class space size is limited to 3G. This can theoretically happen if the CDS archive
158 // is larger than 1G and class space size is set to the maximum possible 3G.
159 vm_exit_during_initialization("Sum of CDS archive size and class space size exceed 4 GB");
160 }
161
162 const size_t encoding_range_size = nth_bit(narrow_klass_pointer_bits() + requested_shift);
163 address encoding_range_end = requested_base + encoding_range_size;
164
165 // Note: it would be technically valid for the encoding base to precede the start of the Klass range. But we only call
166 // this function from CDS, and therefore know this to be true.
167 assert(requested_base == addr, "Invalid requested base");
168
169 _base = requested_base;
170 _shift = requested_shift;
171 _range = encoding_range_size;
172
173 #ifdef ASSERT
174 _klass_range_start = addr;
175 _klass_range_end = addr + len;
176 calc_lowest_highest_narrow_klass_id();
177 sanity_check_after_initialization();
178 #endif
179
180 DEBUG_ONLY(sanity_check_after_initialization();)
181 }
182
183 char* CompressedKlassPointers::reserve_address_space_X(uintptr_t from, uintptr_t to, size_t size, size_t alignment, bool aslr) {
184 alignment = MAX2(Metaspace::reserve_alignment(), alignment);
185 return os::attempt_reserve_memory_between((char*)from, (char*)to, size, alignment, aslr);
186 }
187
188 char* CompressedKlassPointers::reserve_address_space_for_unscaled_encoding(size_t size, bool aslr) {
189 if (tiny_classpointer_mode()) {
190 return nullptr;
191 }
192 const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
193 return reserve_address_space_X(0, unscaled_max, size, Metaspace::reserve_alignment(), aslr);
194 }
195
196 char* CompressedKlassPointers::reserve_address_space_for_zerobased_encoding(size_t size, bool aslr) {
197 if (tiny_classpointer_mode()) {
198 return nullptr;
199 }
200 const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
201 const size_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
202 return reserve_address_space_X(unscaled_max, zerobased_max, size, Metaspace::reserve_alignment(), aslr);
203 }
204
205 char* CompressedKlassPointers::reserve_address_space_for_16bit_move(size_t size, bool aslr) {
206 return reserve_address_space_X(nth_bit(32), nth_bit(48), size, nth_bit(32), aslr);
207 }
208
209 void CompressedKlassPointers::initialize(address addr, size_t len) {
210
211 if (len > max_klass_range_size) {
212 // Class space size is limited to 3G. This can theoretically happen if the CDS archive
213 // is larger than 1G and class space size is set to the maximum possible 3G.
214 vm_exit_during_initialization("Sum of CDS archive size and class space size exceed 4 GB");
215 }
216
217 // Give CPU a shot at a specialized init sequence
218 #ifndef ZERO
219 if (pd_initialize(addr, len)) {
220 return;
221 }
222 #endif
223
224 if (tiny_classpointer_mode()) {
225
226 // This handles the case that we - experimentally - reduce the number of
227 // class pointer bits further, such that (shift + num bits) < 32.
228 assert(len <= (size_t)nth_bit(narrow_klass_pointer_bits() + max_shift()),
229 "klass range size exceeds encoding");
230
231 // In tiny classpointer mode, we don't attempt for zero-based mode.
232 // Instead, we set the base to the start of the klass range and then try
233 // for the smallest shift possible that still covers the whole range.
234 // The reason is that we want to avoid, if possible, shifts larger than
235 // a cacheline size.
236 _base = addr;
237 _range = len;
238
239 if (TinyClassPointerShift != 0) {
240 _shift = TinyClassPointerShift;
241 } else {
242 constexpr int log_cacheline = 6;
243 int s = max_shift();
244 while (s > log_cacheline && ((size_t)nth_bit(narrow_klass_pointer_bits() + s - 1) > len)) {
245 s--;
246 }
247 _shift = s;
248 }
249
250 } else {
251
252 // In legacy mode, we try, in order of preference:
253 // -unscaled (base=0 shift=0)
254 // -zero-based (base=0 shift>0)
255 // -nonzero-base (base>0 shift=0)
256 // Note that base>0 shift>0 should never be needed, since the klass range will
257 // never exceed 4GB.
258 const uintptr_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
259 const uintptr_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
260
261 address const end = addr + len;
262 if (end <= (address)unscaled_max) {
263 _base = nullptr;
264 _shift = 0;
265 } else {
266 if (end <= (address)zerobased_max) {
267 _base = nullptr;
268 _shift = max_shift();
269 } else {
270 _base = addr;
271 _shift = 0;
272 }
273 }
274 _range = end - _base;
275
276 }
277
278 #ifdef ASSERT
279 _klass_range_start = addr;
280 _klass_range_end = addr + len;
281 calc_lowest_highest_narrow_klass_id();
282 sanity_check_after_initialization();
283 #endif
284 }
285
286 void CompressedKlassPointers::print_mode(outputStream* st) {
287 st->print_cr("UseCompressedClassPointers %d, UseCompactObjectHeaders %d, "
288 "narrow klass pointer bits %d, max shift %d",
289 UseCompressedClassPointers, UseCompactObjectHeaders,
290 _narrow_klass_pointer_bits, _max_shift);
291 if (_base == (address)-1) {
292 st->print_cr("Narrow klass encoding not initialized");
293 return;
294 }
295 st->print_cr("Narrow klass base: " PTR_FORMAT ", Narrow klass shift: %d, "
296 "Narrow klass range: " SIZE_FORMAT_X, p2i(base()), shift(),
297 range());
298 #ifdef ASSERT
299 st->print_cr("Klass range: [" PTR_FORMAT "," PTR_FORMAT ")",
300 p2i(_klass_range_start), p2i(_klass_range_end));
301 st->print_cr("Lowest valid nklass id: %u Highest valid nklass id: %u",
302 _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id);
303 #endif
304 }
305
306 #endif // _LP64