1 /*
2 * Copyright (c) 2019, 2024, 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 "memory/metaspace.hpp"
28 #include "oops/compressedKlass.inline.hpp"
29 #include "runtime/globals.hpp"
30 #include "runtime/java.hpp"
31 #include "runtime/os.hpp"
32 #include "utilities/debug.hpp"
33 #include "utilities/globalDefinitions.hpp"
34 #include "utilities/ostream.hpp"
35
36 int CompressedKlassPointers::_narrow_klass_pointer_bits = -1;
37 int CompressedKlassPointers::_max_shift = -1;
38
39 address CompressedKlassPointers::_base = (address)-1;
40 int CompressedKlassPointers::_shift = -1;
41 address CompressedKlassPointers::_klass_range_start = nullptr;
42 address CompressedKlassPointers::_klass_range_end = nullptr;
43 narrowKlass CompressedKlassPointers::_lowest_valid_narrow_klass_id = (narrowKlass)-1;
44 narrowKlass CompressedKlassPointers::_highest_valid_narrow_klass_id = (narrowKlass)-1;
45
46 #ifdef _LP64
47
48 size_t CompressedKlassPointers::max_klass_range_size() {
49 // We disallow klass range sizes larger than 4GB even if the encoding
50 // range would allow for a larger Klass range (e.g. Base=zero, shift=3 -> 32GB).
51 // That is because many CPU-specific compiler decodings do not want the
52 // shifted narrow Klass to spill over into the third quadrant of the 64-bit target
53 // address, e.g. to use a 16-bit move for a simplified base addition.
54 return MIN2(4 * G, max_encoding_range_size());
55 }
56
57 void CompressedKlassPointers::pre_initialize() {
58 if (UseCompactObjectHeaders) {
59 _narrow_klass_pointer_bits = narrow_klass_pointer_bits_coh;
60 _max_shift = max_shift_coh;
61 } else {
62 _narrow_klass_pointer_bits = narrow_klass_pointer_bits_noncoh;
63 _max_shift = max_shift_noncoh;
64 }
65 }
66
67 #ifdef ASSERT
68 void CompressedKlassPointers::sanity_check_after_initialization() {
69 // In expectation of an assert, prepare condensed info to be printed with the assert.
70 char tmp[256];
71 os::snprintf(tmp, sizeof(tmp), "klass range: " RANGE2FMT ","
72 " base " PTR_FORMAT ", shift %d, lowest/highest valid narrowKlass %u/%u",
73 RANGE2FMTARGS(_klass_range_start, _klass_range_end),
74 p2i(_base), _shift, _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id);
75 #define ASSERT_HERE(cond) assert(cond, " (%s)", tmp);
76 #define ASSERT_HERE_2(cond, msg) assert(cond, msg " (%s)", tmp);
77
78 // There is no technical reason preventing us from using other klass pointer bit lengths,
79 // but it should be a deliberate choice
80 ASSERT_HERE(_narrow_klass_pointer_bits == 32 || _narrow_klass_pointer_bits == 19);
81
82 // All values must be inited
83 ASSERT_HERE(_max_shift != -1);
84 ASSERT_HERE(_klass_range_start != (address)-1);
85 ASSERT_HERE(_klass_range_end != (address)-1);
86 ASSERT_HERE(_lowest_valid_narrow_klass_id != (narrowKlass)-1);
87 ASSERT_HERE(_base != (address)-1);
88 ASSERT_HERE(_shift != -1);
89
90 const size_t klass_align = klass_alignment_in_bytes();
91
92 // must be aligned enough hold 64-bit data
93 ASSERT_HERE(is_aligned(klass_align, sizeof(uint64_t)));
94
95 // should be smaller than the minimum metaspace chunk size (soft requirement)
96 ASSERT_HERE(klass_align <= K);
97
98 ASSERT_HERE(_klass_range_end > _klass_range_start);
99
100 // Check that Klass range is fully engulfed in the encoding range
101 const address encoding_start = _base;
102 const address encoding_end = _base + nth_bit(narrow_klass_pointer_bits() + _shift);
103 ASSERT_HERE_2(_klass_range_start >= _base && _klass_range_end <= encoding_end,
104 "Resulting encoding range does not fully cover the class range");
105
106 // Check that Klass range is aligned to Klass alignment. Note that this should never be
107 // an issue since the Klass range is handed in by either CDS- or Metaspace-initialization, and
108 // it should be the result of an mmap operation that operates on page sizes. So as long as
109 // the Klass alignment is <= page size, we are fine.
110 ASSERT_HERE_2(is_aligned(_klass_range_start, klass_align) &&
111 is_aligned(_klass_range_end, klass_align),
112 "Klass range must start and end at a properly aligned address");
113
114 // Check _lowest_valid_narrow_klass_id and _highest_valid_narrow_klass_id
115 ASSERT_HERE_2(_lowest_valid_narrow_klass_id > 0, "Null is not a valid narrowKlass");
116 ASSERT_HERE(_highest_valid_narrow_klass_id > _lowest_valid_narrow_klass_id);
117
118 Klass* const k1 = decode_not_null_without_asserts(_lowest_valid_narrow_klass_id, _base, _shift);
119 if (encoding_start == _klass_range_start) {
120 ASSERT_HERE_2((address)k1 == _klass_range_start + klass_align, "Not lowest");
121 } else {
122 ASSERT_HERE_2((address)k1 == _klass_range_start, "Not lowest");
123 }
124 narrowKlass nk1 = encode_not_null_without_asserts(k1, _base, _shift);
125 ASSERT_HERE_2(nk1 == _lowest_valid_narrow_klass_id, "not reversible");
126
127 Klass* const k2 = decode_not_null_without_asserts(_highest_valid_narrow_klass_id, _base, _shift);
128 ASSERT_HERE((address)k2 == _klass_range_end - klass_align);
129 narrowKlass nk2 = encode_not_null_without_asserts(k2, _base, _shift);
130 ASSERT_HERE_2(nk2 == _highest_valid_narrow_klass_id, "not reversible");
131
132 #ifdef AARCH64
133 // On aarch64, we never expect a shift value > 0 in standard (non-coh) mode
134 ASSERT_HERE_2(UseCompactObjectHeaders || _shift == 0, "Shift > 0 in non-coh mode?");
135 #endif
136 #undef ASSERT_HERE
137 #undef ASSERT_HERE_2
138 }
139 #endif // ASSERT
140
141 // Helper function: given current Klass Range, Base and Shift, calculate the lowest and highest values
142 // of narrowKlass we can expect.
143 void CompressedKlassPointers::calc_lowest_highest_narrow_klass_id() {
144 address lowest_possible_klass_location = _klass_range_start;
145
146 // A Klass will never be placed at the Encoding range start, since that would translate to a narrowKlass=0, which
147 // is disallowed. Note that both Metaspace and CDS prvent allocation at the first address for this reason.
148 if (lowest_possible_klass_location == _base) {
149 lowest_possible_klass_location += klass_alignment_in_bytes();
150 }
151 _lowest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(lowest_possible_klass_location - _base) >> _shift);
152
153 address highest_possible_klass_location = _klass_range_end - klass_alignment_in_bytes();
154 _highest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(highest_possible_klass_location - _base) >> _shift);
155 }
156
157 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
158 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
159 // archived heap objects.
160 void CompressedKlassPointers::initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift) {
161 if (len > max_klass_range_size()) {
162 stringStream ss;
163 ss.print("Class space size and CDS archive size combined (%zu) "
164 "exceed the maximum possible size (%zu)",
165 len, max_klass_range_size());
166 vm_exit_during_initialization(ss.base());
167 }
168
169 // Note: While it would be technically valid for the encoding base to precede the start of the Klass range,
170 // we never do this here. This is used at CDS runtime to re-instate the scheme used to precompute the
171 // narrow Klass IDs in the archive, and the requested base should point to the start of the Klass range.
172 assert(requested_base == addr, "Invalid requested base");
173
174 // Remember Klass range:
175 _klass_range_start = addr;
176 _klass_range_end = addr + len;
177
178 _base = requested_base;
179 _shift = requested_shift;
180
181 calc_lowest_highest_narrow_klass_id();
182
183 DEBUG_ONLY(sanity_check_after_initialization();)
184 }
185
186 char* CompressedKlassPointers::reserve_address_space_X(uintptr_t from, uintptr_t to, size_t size, size_t alignment, bool aslr) {
187 alignment = MAX2(Metaspace::reserve_alignment(), alignment);
188 return os::attempt_reserve_memory_between((char*)from, (char*)to, size, alignment, aslr);
189 }
190
191 char* CompressedKlassPointers::reserve_address_space_for_unscaled_encoding(size_t size, bool aslr) {
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 const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
198 const size_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
199 return reserve_address_space_X(unscaled_max, zerobased_max, size, Metaspace::reserve_alignment(), aslr);
200 }
201
202 char* CompressedKlassPointers::reserve_address_space_for_16bit_move(size_t size, bool aslr) {
203 return reserve_address_space_X(nth_bit(32), nth_bit(48), size, nth_bit(32), aslr);
204 }
205
206 void CompressedKlassPointers::initialize(address addr, size_t len) {
207
208 if (len > max_klass_range_size()) {
209 stringStream ss;
210 ss.print("Class space size (%zu) exceeds the maximum possible size (%zu)",
211 len, max_klass_range_size());
212 vm_exit_during_initialization(ss.base());
213 }
214
215 // Remember the Klass range:
216 _klass_range_start = addr;
217 _klass_range_end = addr + len;
218
219 // Calculate Base and Shift:
220
221 if (UseCompactObjectHeaders) {
222
223 // This handles the case that we - experimentally - reduce the number of
224 // class pointer bits further, such that (shift + num bits) < 32.
225 assert(len <= (size_t)nth_bit(narrow_klass_pointer_bits() + max_shift()),
226 "klass range size exceeds encoding, len: " SIZE_FORMAT ", narrow_klass_pointer_bits: %d, max_shift: %d", len, narrow_klass_pointer_bits(), max_shift());
227
228 // In compact object header mode, with 19-bit narrowKlass, we don't attempt for
229 // zero-based mode. Instead, we set the base to the start of the klass range and
230 // then try for the smallest shift possible that still covers the whole range.
231 // The reason is that we want to avoid, if possible, shifts larger than
232 // a cacheline size.
233 _base = addr;
234
235 const int log_cacheline = exact_log2(DEFAULT_CACHE_LINE_SIZE);
236 int s = max_shift();
237 while (s > log_cacheline && ((size_t)nth_bit(narrow_klass_pointer_bits() + s - 1) > len)) {
238 s--;
239 }
240 _shift = s;
241
242 } else {
243
244 // Traditional (non-compact) header mode
245 const uintptr_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
246 const uintptr_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
247
248 #ifdef AARCH64
249 // Aarch64 avoids zero-base shifted mode (_base=0 _shift>0), instead prefers
250 // non-zero-based mode with a zero shift.
251 _shift = 0;
252 address const end = addr + len;
253 _base = (end <= (address)unscaled_max) ? nullptr : addr;
254 #else
255 // We try, in order of preference:
256 // -unscaled (base=0 shift=0)
257 // -zero-based (base=0 shift>0)
258 // -nonzero-base (base>0 shift=0)
259 // Note that base>0 shift>0 should never be needed, since the klass range will
260 // never exceed 4GB.
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 #endif // AARCH64
275 }
276
277 calc_lowest_highest_narrow_klass_id();
278
279 #ifdef ASSERT
280 sanity_check_after_initialization();
281 #endif
282 }
283
284 void CompressedKlassPointers::print_mode(outputStream* st) {
285 st->print_cr("UseCompressedClassPointers %d, UseCompactObjectHeaders %d",
286 UseCompressedClassPointers, UseCompactObjectHeaders);
287 if (UseCompressedClassPointers) {
288 st->print_cr("Narrow klass pointer bits %d, Max shift %d",
289 _narrow_klass_pointer_bits, _max_shift);
290 st->print_cr("Narrow klass base: " PTR_FORMAT ", Narrow klass shift: %d",
291 p2i(base()), shift());
292 st->print_cr("Encoding Range: " RANGE2FMT, RANGE2FMTARGS(_base, encoding_range_end()));
293 st->print_cr("Klass Range: " RANGE2FMT, RANGE2FMTARGS(_klass_range_start, _klass_range_end));
294 st->print_cr("Klass ID Range: [%u - %u) (%u)", _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id + 1,
295 _highest_valid_narrow_klass_id + 1 - _lowest_valid_narrow_klass_id);
296 } else {
297 st->print_cr("UseCompressedClassPointers off");
298 }
299 }
300
301 #endif // _LP64