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 #ifdef _LP64
48
49 size_t CompressedKlassPointers::max_klass_range_size() {
50 // We disallow klass range sizes larger than 4GB even if the encoding
51 // range would allow for a larger Klass range (e.g. Base=zero, shift=3 -> 32GB).
52 // That is because many CPU-specific compiler decodings do not want the
53 // shifted narrow Klass to spill over into the third quadrant of the 64-bit target
54 // address, e.g. to use a 16-bit move for a simplified base addition.
55 return MIN2(4 * G, max_encoding_range_size());
56 }
57
58 void CompressedKlassPointers::pre_initialize() {
59 if (UseCompactObjectHeaders) {
60 _narrow_klass_pointer_bits = narrow_klass_pointer_bits_coh;
61 _max_shift = max_shift_coh;
62 } else {
63 _narrow_klass_pointer_bits = narrow_klass_pointer_bits_noncoh;
64 _max_shift = max_shift_noncoh;
65 }
66 }
67
68 #ifdef ASSERT
69 void CompressedKlassPointers::sanity_check_after_initialization() {
70 // In expectation of an assert, prepare condensed info to be printed with the assert.
71 char tmp[256];
72 os::snprintf(tmp, sizeof(tmp), "klass range: " RANGE2FMT ","
73 " base " PTR_FORMAT ", shift %d, lowest/highest valid narrowKlass %u/%u",
74 RANGE2FMTARGS(_klass_range_start, _klass_range_end),
75 p2i(_base), _shift, _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id);
76 #define ASSERT_HERE(cond) assert(cond, " (%s)", tmp);
77 #define ASSERT_HERE_2(cond, msg) assert(cond, msg " (%s)", tmp);
78
79 // All values must be inited
80 ASSERT_HERE(_max_shift != -1);
81 ASSERT_HERE(_klass_range_start != (address)-1);
82 ASSERT_HERE(_klass_range_end != (address)-1);
83 ASSERT_HERE(_lowest_valid_narrow_klass_id != (narrowKlass)-1);
84 ASSERT_HERE(_base != (address)-1);
85 ASSERT_HERE(_shift != -1);
86
87 const size_t klass_align = klass_alignment_in_bytes();
88
89 // must be aligned enough hold 64-bit data
90 ASSERT_HERE(is_aligned(klass_align, sizeof(uint64_t)));
91
92 // should be smaller than the minimum metaspace chunk size (soft requirement)
93 ASSERT_HERE(klass_align <= K);
94
95 ASSERT_HERE(_klass_range_end > _klass_range_start);
96
97 // Check that Klass range is fully engulfed in the encoding range
98 const address encoding_start = _base;
99 const address encoding_end = (address)(p2u(_base) + (uintptr_t)nth_bit(narrow_klass_pointer_bits() + _shift));
100 ASSERT_HERE_2(_klass_range_start >= _base && _klass_range_end <= encoding_end,
101 "Resulting encoding range does not fully cover the class range");
102
103 // Check that Klass range is aligned to Klass alignment. Note that this should never be
104 // an issue since the Klass range is handed in by either CDS- or Metaspace-initialization, and
105 // it should be the result of an mmap operation that operates on page sizes. So as long as
106 // the Klass alignment is <= page size, we are fine.
107 ASSERT_HERE_2(is_aligned(_klass_range_start, klass_align) &&
108 is_aligned(_klass_range_end, klass_align),
109 "Klass range must start and end at a properly aligned address");
110
111 // Check _lowest_valid_narrow_klass_id and _highest_valid_narrow_klass_id
112 ASSERT_HERE_2(_lowest_valid_narrow_klass_id > 0, "Null is not a valid narrowKlass");
113 ASSERT_HERE(_highest_valid_narrow_klass_id > _lowest_valid_narrow_klass_id);
114
115 Klass* const k1 = decode_not_null_without_asserts(_lowest_valid_narrow_klass_id, _base, _shift);
116 if (encoding_start == _klass_range_start) {
117 ASSERT_HERE_2((address)k1 == _klass_range_start + klass_align, "Not lowest");
118 } else {
119 ASSERT_HERE_2((address)k1 == _klass_range_start, "Not lowest");
120 }
121 narrowKlass nk1 = encode_not_null_without_asserts(k1, _base, _shift);
122 ASSERT_HERE_2(nk1 == _lowest_valid_narrow_klass_id, "not reversible");
123
124 Klass* const k2 = decode_not_null_without_asserts(_highest_valid_narrow_klass_id, _base, _shift);
125 ASSERT_HERE((address)k2 == _klass_range_end - klass_align);
126 narrowKlass nk2 = encode_not_null_without_asserts(k2, _base, _shift);
127 ASSERT_HERE_2(nk2 == _highest_valid_narrow_klass_id, "not reversible");
128
129 #ifdef AARCH64
130 // On aarch64, we never expect a shift value > 0 in standard (non-coh) mode
131 ASSERT_HERE_2(UseCompactObjectHeaders || _shift == 0, "Shift > 0 in non-coh mode?");
132 #endif
133 #undef ASSERT_HERE
134 #undef ASSERT_HERE_2
135 }
136 #endif // ASSERT
137
138 // Helper function: given current Klass Range, Base and Shift, calculate the lowest and highest values
139 // of narrowKlass we can expect.
140 void CompressedKlassPointers::calc_lowest_highest_narrow_klass_id() {
141 address lowest_possible_klass_location = _klass_range_start;
142
143 // A Klass will never be placed at the Encoding range start, since that would translate to a narrowKlass=0, which
144 // is disallowed. Note that both Metaspace and CDS prvent allocation at the first address for this reason.
145 if (lowest_possible_klass_location == _base) {
146 lowest_possible_klass_location += klass_alignment_in_bytes();
147 }
148 _lowest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(lowest_possible_klass_location - _base) >> _shift);
149
150 address highest_possible_klass_location = _klass_range_end - klass_alignment_in_bytes();
151 _highest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(highest_possible_klass_location - _base) >> _shift);
152 }
153
154 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
155 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
156 // archived heap objects.
157 void CompressedKlassPointers::initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift) {
158 if (len > max_klass_range_size()) {
159 stringStream ss;
160 ss.print("Class space size and CDS archive size combined (%zu) "
161 "exceed the maximum possible size (%zu)",
162 len, max_klass_range_size());
163 vm_exit_during_initialization(ss.base());
164 }
165
166 // Remember Klass range:
167 _klass_range_start = addr;
168 _klass_range_end = addr + len;
169
170 _base = requested_base;
171 _shift = requested_shift;
172
173 calc_lowest_highest_narrow_klass_id();
174
175 // This has already been checked for SharedBaseAddress and if this fails, it's a bug in the allocation code.
176 if (!set_klass_decode_mode()) {
177 fatal("base=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
178 p2i(_base), _shift);
179 }
180
181 DEBUG_ONLY(sanity_check_after_initialization();)
182 }
183
184 char* CompressedKlassPointers::reserve_address_space_X(uintptr_t from, uintptr_t to, size_t size, size_t alignment, bool aslr) {
185 alignment = MAX2(Metaspace::reserve_alignment(), alignment);
186 return os::attempt_reserve_memory_between((char*)from, (char*)to, size, alignment, aslr);
187 }
188
189 char* CompressedKlassPointers::reserve_address_space_for_unscaled_encoding(size_t size, bool aslr) {
190 const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
191 return reserve_address_space_X(0, unscaled_max, size, Metaspace::reserve_alignment(), aslr);
192 }
193
194 char* CompressedKlassPointers::reserve_address_space_for_zerobased_encoding(size_t size, bool aslr) {
195 const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
196 const size_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
197 return reserve_address_space_X(unscaled_max, zerobased_max, size, Metaspace::reserve_alignment(), aslr);
198 }
199
200 char* CompressedKlassPointers::reserve_address_space_for_16bit_move(size_t size, bool aslr) {
201 return reserve_address_space_X(nth_bit(32), nth_bit(48), size, nth_bit(32), aslr);
202 }
203
204 void CompressedKlassPointers::initialize(address addr, size_t len) {
205
206 if (len > max_klass_range_size()) {
207 stringStream ss;
208 ss.print("Class space size (%zu) exceeds the maximum possible size (%zu)",
209 len, max_klass_range_size());
210 vm_exit_during_initialization(ss.base());
211 }
212
213 // Remember the Klass range:
214 _klass_range_start = addr;
215 _klass_range_end = addr + len;
216
217 // Calculate Base and Shift:
218
219 if (UseCompactObjectHeaders) {
220
221 // In compact object header mode, with 22-bit narrowKlass, we don't attempt for
222 // zero-based mode. Instead, we set the base to the start of the klass range and
223 // then try for the smallest shift possible that still covers the whole range.
224 // The reason is that we want to avoid, if possible, shifts larger than
225 // a cacheline size.
226 _base = addr;
227
228 const int log_cacheline = exact_log2(DEFAULT_CACHE_LINE_SIZE);
229 int s = max_shift();
230 while (s > log_cacheline && ((size_t)nth_bit(narrow_klass_pointer_bits() + s - 1) > len)) {
231 s--;
232 }
233 _shift = s;
234
235 } else {
236
237 // Traditional (non-compact) header mode
238 const uintptr_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
239 const uintptr_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
240
241 #ifdef AARCH64
242 // Aarch64 avoids zero-base shifted mode (_base=0 _shift>0), instead prefers
243 // non-zero-based mode with a zero shift.
244 _shift = 0;
245 address const end = addr + len;
246 _base = (end <= (address)unscaled_max) ? nullptr : addr;
247 #else
248 // We try, in order of preference:
249 // -unscaled (base=0 shift=0)
250 // -zero-based (base=0 shift>0)
251 // -nonzero-base (base>0 shift=0)
252 // Note that base>0 shift>0 should never be needed, since the klass range will
253 // never exceed 4GB.
254 address const end = addr + len;
255 if (end <= (address)unscaled_max) {
256 _base = nullptr;
257 _shift = 0;
258 } else {
259 if (end <= (address)zerobased_max) {
260 _base = nullptr;
261 _shift = max_shift();
262 } else {
263 _base = addr;
264 _shift = 0;
265 }
266 }
267 #endif // AARCH64
268 }
269
270 calc_lowest_highest_narrow_klass_id();
271
272 // Initialize klass decode mode and check compability with decode instructions
273 if (!set_klass_decode_mode()) {
274
275 // Give fatal error if this is a specified address
276 if (CompressedClassSpaceBaseAddress == (size_t)_base) {
277 vm_exit_during_initialization(
278 err_msg("CompressedClassSpaceBaseAddress=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
279 CompressedClassSpaceBaseAddress, _shift));
280 } else {
281 // If this fails, it's a bug in the allocation code.
282 fatal("CompressedClassSpaceBaseAddress=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
283 p2i(_base), _shift);
284 }
285 }
286 #ifdef ASSERT
287 sanity_check_after_initialization();
288 #endif
289 }
290
291 void CompressedKlassPointers::print_mode(outputStream* st) {
292 st->print_cr("UseCompressedClassPointers %d, UseCompactObjectHeaders %d",
293 UseCompressedClassPointers, UseCompactObjectHeaders);
294 if (UseCompressedClassPointers) {
295 st->print_cr("Narrow klass pointer bits %d, Max shift %d",
296 _narrow_klass_pointer_bits, _max_shift);
297 st->print_cr("Narrow klass base: " PTR_FORMAT ", Narrow klass shift: %d",
298 p2i(base()), shift());
299 st->print_cr("Encoding Range: " RANGE2FMT, RANGE2FMTARGS(_base, encoding_range_end()));
300 st->print_cr("Klass Range: " RANGE2FMT, RANGE2FMTARGS(_klass_range_start, _klass_range_end));
301 st->print_cr("Klass ID Range: [%u - %u) (%u)", _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id + 1,
302 _highest_valid_narrow_klass_id + 1 - _lowest_valid_narrow_klass_id);
303 if (_protection_zone_size > 0) {
304 st->print_cr("Protection zone: " RANGEFMT, RANGEFMTARGS(_base, _protection_zone_size));
305 } else {
306 st->print_cr("No protection zone.");
307 }
308 } else {
309 st->print_cr("UseCompressedClassPointers off");
310 }
311 }
312
313 // On AIX, we cannot mprotect archive space or class space since they are reserved with SystemV shm.
314 static constexpr bool can_mprotect_archive_space = NOT_AIX(true) AIX_ONLY(false);
315
316 // Protect a zone a the start of the encoding range
317 void CompressedKlassPointers::establish_protection_zone(address addr, size_t size) {
318 assert(_protection_zone_size == 0, "just once");
319 assert(addr == base(), "Protection zone not at start of encoding range?");
320 assert(size > 0 && is_aligned(size, os::vm_page_size()), "Protection zone not page sized");
321 const bool rc = can_mprotect_archive_space && os::protect_memory((char*)addr, size, os::MEM_PROT_NONE, false);
322 log_info(metaspace)("%s Narrow Klass Protection zone " RANGEFMT,
323 (rc ? "Established" : "FAILED to establish "),
324 RANGEFMTARGS(addr, size));
325 if (!rc) {
326 // If we fail to establish the protection zone, we fill it with a clear pattern to make it
327 // stick out in register values (0x50 aka 'P', repeated)
328 os::commit_memory((char*)addr, size, false);
329 memset(addr, 'P', size);
330 }
331 _protection_zone_size = size;
332 }
333
334 bool CompressedKlassPointers::is_in_protection_zone(address addr) {
335 return _protection_zone_size > 0 ?
336 (addr >= base() && addr < base() + _protection_zone_size) : false;
337 }
338
339 #endif // _LP64