1 /*
2 * Copyright (c) 2019, 2025, 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 "logging/log.hpp"
26 #include "memory/metaspace.hpp"
27 #include "oops/compressedKlass.inline.hpp"
28 #include "runtime/globals.hpp"
29 #include "runtime/java.hpp"
30 #include "runtime/os.hpp"
31 #include "utilities/debug.hpp"
32 #include "utilities/formatBuffer.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 size_t CompressedKlassPointers::_protection_zone_size = 0;
46
47 size_t CompressedKlassPointers::max_klass_range_size() {
48 #ifdef _LP64
49 const size_t encoding_allows = nth_bit(narrow_klass_pointer_bits() + max_shift());
50 constexpr size_t cap = 4 * G;
51 return MIN2(encoding_allows, cap);
52 #else
53 // 32-bit: only 32-bit "narrow" Klass pointers allowed. If we ever support smaller narrow
54 // Klass pointers here, coding needs to be revised.
55 // We keep one page safety zone free to guard against size_t overflows on 32-bit. In practice
56 // this is irrelevant because these upper address space parts are not user-addressable on
57 // any of our 32-bit platforms.
58 return align_down(UINT_MAX, os::vm_page_size());
59 #endif
60 }
61
62 void CompressedKlassPointers::pre_initialize() {
63 if (UseCompactObjectHeaders) {
64 _narrow_klass_pointer_bits = narrow_klass_pointer_bits_coh;
65 _max_shift = max_shift_coh;
66 } else {
67 #ifdef _LP64
68 _narrow_klass_pointer_bits = narrow_klass_pointer_bits_noncoh;
69 _max_shift = max_shift_noncoh;
70 #else
71 _narrow_klass_pointer_bits = 32;
72 _max_shift = 0;
73 #endif
74 }
75 }
76
77 #ifdef ASSERT
78 void CompressedKlassPointers::sanity_check_after_initialization() {
79 // In expectation of an assert, prepare condensed info to be printed with the assert.
80 char tmp[256];
81 os::snprintf_checked(tmp, sizeof(tmp), "klass range: " RANGE2FMT ","
82 " base " PTR_FORMAT ", shift %d, lowest/highest valid narrowKlass %u/%u",
83 RANGE2FMTARGS(_klass_range_start, _klass_range_end),
84 p2i(_base), _shift, _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id);
85 #define ASSERT_HERE(cond) assert(cond, " (%s)", tmp);
86 #define ASSERT_HERE_2(cond, msg) assert(cond, msg " (%s)", tmp);
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
96 // We should need a class space if address space is larger than what narrowKlass can address
97 const bool should_need_class_space = (BytesPerWord * BitsPerByte) > narrow_klass_pointer_bits();
98 ASSERT_HERE(should_need_class_space == needs_class_space());
99
100 const size_t klass_align = klass_alignment_in_bytes();
101
102 // must be aligned enough hold 64-bit data
103 ASSERT_HERE(is_aligned(klass_align, sizeof(uint64_t)));
104
105 // should be smaller than the minimum metaspace chunk size (soft requirement)
106 ASSERT_HERE(klass_align <= K);
107
108 ASSERT_HERE(_klass_range_end > _klass_range_start);
109
110 // Check that Klass range is fully engulfed in the encoding range
111 const address encoding_start = _base;
112 const address encoding_end = (address)
113 LP64_ONLY((p2u(_base) + (uintptr_t)nth_bit(narrow_klass_pointer_bits() + _shift)))
114 NOT_LP64(max_klass_range_size());
115 ASSERT_HERE_2(_klass_range_start >= _base && _klass_range_end <= encoding_end,
116 "Resulting encoding range does not fully cover the class range");
117
118 // Check that Klass range is aligned to Klass alignment. Note that this should never be
119 // an issue since the Klass range is handed in by either CDS- or Metaspace-initialization, and
120 // it should be the result of an mmap operation that operates on page sizes. So as long as
121 // the Klass alignment is <= page size, we are fine.
122 ASSERT_HERE_2(is_aligned(_klass_range_start, klass_align) &&
123 is_aligned(_klass_range_end, klass_align),
124 "Klass range must start and end at a properly aligned address");
125
126 // Check _lowest_valid_narrow_klass_id and _highest_valid_narrow_klass_id
127 ASSERT_HERE_2(_lowest_valid_narrow_klass_id > 0, "Null is not a valid narrowKlass");
128 ASSERT_HERE(_highest_valid_narrow_klass_id > _lowest_valid_narrow_klass_id);
129
130 Klass* const k1 = decode_not_null_without_asserts(_lowest_valid_narrow_klass_id, _base, _shift);
131 if (encoding_start == _klass_range_start) {
132 ASSERT_HERE_2((address)k1 == _klass_range_start + klass_align, "Not lowest");
133 } else {
134 ASSERT_HERE_2((address)k1 == _klass_range_start, "Not lowest");
135 }
136 narrowKlass nk1 = encode_not_null_without_asserts(k1, _base, _shift);
137 ASSERT_HERE_2(nk1 == _lowest_valid_narrow_klass_id, "not reversible");
138
139 Klass* const k2 = decode_not_null_without_asserts(_highest_valid_narrow_klass_id, _base, _shift);
140 ASSERT_HERE((address)k2 == _klass_range_end - klass_align);
141 narrowKlass nk2 = encode_not_null_without_asserts(k2, _base, _shift);
142 ASSERT_HERE_2(nk2 == _highest_valid_narrow_klass_id, "not reversible");
143
144 #ifdef AARCH64
145 // On aarch64, we never expect a shift value > 0 in standard (non-coh) mode
146 ASSERT_HERE_2(UseCompactObjectHeaders || _shift == 0, "Shift > 0 in non-coh mode?");
147 #endif
148 #undef ASSERT_HERE
149 #undef ASSERT_HERE_2
150 }
151 #endif // ASSERT
152
153 // Helper function: given current Klass Range, Base and Shift, calculate the lowest and highest values
154 // of narrowKlass we can expect.
155 void CompressedKlassPointers::calc_lowest_highest_narrow_klass_id() {
156 address lowest_possible_klass_location = _klass_range_start;
157
158 // A Klass will never be placed at the Encoding range start, since that would translate to a narrowKlass=0, which
159 // is disallowed. If the encoding range starts at the klass range start, both Metaspace and CDS establish an
160 // mprotected zone for this reason (see establish_protection_zone).
161 if (lowest_possible_klass_location == _base) {
162 lowest_possible_klass_location += klass_alignment_in_bytes();
163 }
164 _lowest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(lowest_possible_klass_location - _base) >> _shift);
165
166 address highest_possible_klass_location = _klass_range_end - klass_alignment_in_bytes();
167 _highest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(highest_possible_klass_location - _base) >> _shift);
168 }
169
170 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
171 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
172 // archived heap objects.
173 void CompressedKlassPointers::initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift) {
174 if (len > max_klass_range_size()) {
175 stringStream ss;
176 ss.print("Class space size and CDS archive size combined (%zu) "
177 "exceed the maximum possible size (%zu)",
178 len, max_klass_range_size());
179 vm_exit_during_initialization(ss.base());
180 }
181
182 // Remember Klass range:
183 _klass_range_start = addr;
184 _klass_range_end = addr + len;
185
186 _base = requested_base;
187 _shift = requested_shift;
188
189 calc_lowest_highest_narrow_klass_id();
190
191 // This has already been checked for SharedBaseAddress and if this fails, it's a bug in the allocation code.
192 if (!set_klass_decode_mode()) {
193 fatal("base=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
194 p2i(_base), _shift);
195 }
196
197 DEBUG_ONLY(sanity_check_after_initialization();)
198 }
199
200 char* CompressedKlassPointers::reserve_address_space_X(uintptr_t from, uintptr_t to, size_t size, size_t alignment, bool aslr) {
201 alignment = MAX2(Metaspace::reserve_alignment(), alignment);
202 return os::attempt_reserve_memory_between((char*)from, (char*)to, size, alignment, aslr);
203 }
204
205 char* CompressedKlassPointers::reserve_address_space_below_4G(size_t size, bool aslr) {
206 return reserve_address_space_X(0, nth_bit(32), size, Metaspace::reserve_alignment(), aslr);
207 }
208
209 char* CompressedKlassPointers::reserve_address_space_for_unscaled_encoding(size_t size, bool aslr) {
210 const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
211 return reserve_address_space_X(0, unscaled_max, size, Metaspace::reserve_alignment(), aslr);
212 }
213
214 char* CompressedKlassPointers::reserve_address_space_for_zerobased_encoding(size_t size, bool aslr) {
215 const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
216 const size_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
217 return reserve_address_space_X(unscaled_max, zerobased_max, size, Metaspace::reserve_alignment(), aslr);
218 }
219
220 char* CompressedKlassPointers::reserve_address_space_for_16bit_move(size_t size, bool aslr) {
221 return reserve_address_space_X(nth_bit(32), nth_bit(48), size, nth_bit(32), aslr);
222 }
223
224 void CompressedKlassPointers::initialize(address addr, size_t len) {
225
226 if (len > max_klass_range_size()) {
227 stringStream ss;
228 ss.print("Class space size (%zu) exceeds the maximum possible size (%zu)",
229 len, max_klass_range_size());
230 vm_exit_during_initialization(ss.base());
231 }
232
233 // Remember the Klass range:
234 _klass_range_start = addr;
235 _klass_range_end = addr + len;
236
237 // Calculate Base and Shift:
238
239 if (UseCompactObjectHeaders) {
240
241 // In compact object header mode, with 22-bit narrowKlass, we don't attempt for
242 // zero-based mode. Instead, we set the base to the start of the klass range and
243 // then try for the smallest shift possible that still covers the whole range.
244 // The reason is that we want to avoid, if possible, shifts larger than
245 // a cacheline size.
246 _base = addr;
247
248 const int log_cacheline = exact_log2(DEFAULT_CACHE_LINE_SIZE);
249 int s = max_shift();
250 while (s > log_cacheline && ((size_t)nth_bit(narrow_klass_pointer_bits() + s - 1) > len)) {
251 s--;
252 }
253 _shift = s;
254
255 } else {
256
257 #ifdef _LP64
258 // Traditional (non-compact) header mode
259 const uintptr_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
260 const uintptr_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
261
262 #ifdef AARCH64
263 // Aarch64 avoids zero-base shifted mode (_base=0 _shift>0), instead prefers
264 // non-zero-based mode with a zero shift.
265 _shift = 0;
266 address const end = addr + len;
267 _base = (end <= (address)unscaled_max) ? nullptr : addr;
268 #else
269
270 // We try, in order of preference:
271 // -unscaled (base=0 shift=0)
272 // -zero-based (base=0 shift>0)
273 // -nonzero-base (base>0 shift=0)
274 // Note that base>0 shift>0 should never be needed, since the klass range will
275 // never exceed 4GB.
276 address const end = addr + len;
277 if (end <= (address)unscaled_max) {
278 _base = nullptr;
279 _shift = 0;
280 } else {
281 if (end <= (address)zerobased_max) {
282 _base = nullptr;
283 _shift = max_shift();
284 } else {
285 _base = addr;
286 _shift = 0;
287 }
288 }
289 #endif // AARCH64
290 #else
291 // 32-bit "compressed class pointer" mode
292 _base = nullptr;
293 _shift = 0;
294 // as our "protection zone", we just assume the lowest protected parts of
295 // the user address space.
296 _protection_zone_size = os::vm_min_address();
297 #endif // LP64
298 }
299
300 calc_lowest_highest_narrow_klass_id();
301
302 // Initialize JIT-specific decoding settings
303 if (!set_klass_decode_mode()) {
304
305 // Give fatal error if this is a specified address
306 if (CompressedClassSpaceBaseAddress == (size_t)_base) {
307 vm_exit_during_initialization(
308 err_msg("CompressedClassSpaceBaseAddress=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
309 CompressedClassSpaceBaseAddress, _shift));
310 } else {
311 // If this fails, it's a bug in the allocation code.
312 fatal("CompressedClassSpaceBaseAddress=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
313 p2i(_base), _shift);
314 }
315 }
316
317 DEBUG_ONLY(sanity_check_after_initialization();)
318 }
319
320 void CompressedKlassPointers::print_mode(outputStream* st) {
321 st->print_cr("UseCompressedClassPointers %d, UseCompactObjectHeaders %d",
322 UseCompressedClassPointers, UseCompactObjectHeaders);
323 if (UseCompressedClassPointers) {
324 st->print_cr("Narrow klass pointer bits %d, Max shift %d",
325 _narrow_klass_pointer_bits, _max_shift);
326 st->print_cr("Narrow klass base: " PTR_FORMAT ", Narrow klass shift: %d",
327 p2i(base()), shift());
328 st->print_cr("Encoding Range: " RANGE2FMT, RANGE2FMTARGS(_base, encoding_range_end()));
329 st->print_cr("Klass Range: " RANGE2FMT, RANGE2FMTARGS(_klass_range_start, _klass_range_end));
330 st->print_cr("Klass ID Range: [%u - %u) (%u)", _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id + 1,
331 _highest_valid_narrow_klass_id + 1 - _lowest_valid_narrow_klass_id);
332 if (_protection_zone_size > 0) {
333 st->print_cr("Protection zone: " RANGEFMT, RANGEFMTARGS(_base, _protection_zone_size));
334 } else {
335 st->print_cr("No protection zone.");
336 }
337 } else {
338 st->print_cr("UseCompressedClassPointers off");
339 }
340 }
341
342 // On AIX, we cannot mprotect archive space or class space since they are reserved with SystemV shm.
343 static constexpr bool can_mprotect_archive_space = NOT_AIX(true) AIX_ONLY(false);
344
345 // Protect a zone a the start of the encoding range
346 void CompressedKlassPointers::establish_protection_zone(address addr, size_t size) {
347 assert(_protection_zone_size == 0, "just once");
348 assert(addr == base(), "Protection zone not at start of encoding range?");
349 assert(size > 0 && is_aligned(size, os::vm_page_size()), "Protection zone not page sized");
350 const bool rc = can_mprotect_archive_space && os::protect_memory((char*)addr, size, os::MEM_PROT_NONE, false);
351 log_info(metaspace)("%s Narrow Klass Protection zone " RANGEFMT,
352 (rc ? "Established" : "FAILED to establish "),
353 RANGEFMTARGS(addr, size));
354 if (!rc) {
355 // If we fail to establish the protection zone, we fill it with a clear pattern to make it
356 // stick out in register values (0x50 aka 'P', repeated)
357 os::commit_memory((char*)addr, size, false);
358 memset(addr, 'P', size);
359 }
360 _protection_zone_size = size;
361 }
362
363 bool CompressedKlassPointers::is_in_protection_zone(address addr) {
364 return _protection_zone_size > 0 ?
365 (addr >= base() && addr < base() + _protection_zone_size) : false;
366 }
367