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 // There is no technical reason preventing us from using other klass pointer bit lengths,
80 // but it should be a deliberate choice
81 ASSERT_HERE(_narrow_klass_pointer_bits == 32 || _narrow_klass_pointer_bits == 19);
82
83 // All values must be inited
84 ASSERT_HERE(_max_shift != -1);
85 ASSERT_HERE(_klass_range_start != (address)-1);
86 ASSERT_HERE(_klass_range_end != (address)-1);
87 ASSERT_HERE(_lowest_valid_narrow_klass_id != (narrowKlass)-1);
88 ASSERT_HERE(_base != (address)-1);
89 ASSERT_HERE(_shift != -1);
90
91 const size_t klass_align = klass_alignment_in_bytes();
92
93 // must be aligned enough hold 64-bit data
94 ASSERT_HERE(is_aligned(klass_align, sizeof(uint64_t)));
95
96 // should be smaller than the minimum metaspace chunk size (soft requirement)
97 ASSERT_HERE(klass_align <= K);
98
99 ASSERT_HERE(_klass_range_end > _klass_range_start);
100
101 // Check that Klass range is fully engulfed in the encoding range
102 const address encoding_start = _base;
103 const address encoding_end = (address)(p2u(_base) + (uintptr_t)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. Note that this should never be
108 // an issue since the Klass range is handed in by either CDS- or Metaspace-initialization, and
109 // it should be the result of an mmap operation that operates on page sizes. So as long as
110 // the Klass alignment is <= page size, we are fine.
111 ASSERT_HERE_2(is_aligned(_klass_range_start, klass_align) &&
112 is_aligned(_klass_range_end, klass_align),
113 "Klass range must start and end at a properly aligned address");
114
115 // Check _lowest_valid_narrow_klass_id and _highest_valid_narrow_klass_id
116 ASSERT_HERE_2(_lowest_valid_narrow_klass_id > 0, "Null is not a valid narrowKlass");
117 ASSERT_HERE(_highest_valid_narrow_klass_id > _lowest_valid_narrow_klass_id);
118
119 Klass* const k1 = decode_not_null_without_asserts(_lowest_valid_narrow_klass_id, _base, _shift);
120 if (encoding_start == _klass_range_start) {
121 ASSERT_HERE_2((address)k1 == _klass_range_start + klass_align, "Not lowest");
122 } else {
123 ASSERT_HERE_2((address)k1 == _klass_range_start, "Not lowest");
124 }
125 narrowKlass nk1 = encode_not_null_without_asserts(k1, _base, _shift);
126 ASSERT_HERE_2(nk1 == _lowest_valid_narrow_klass_id, "not reversible");
127
128 Klass* const k2 = decode_not_null_without_asserts(_highest_valid_narrow_klass_id, _base, _shift);
129 ASSERT_HERE((address)k2 == _klass_range_end - klass_align);
130 narrowKlass nk2 = encode_not_null_without_asserts(k2, _base, _shift);
131 ASSERT_HERE_2(nk2 == _highest_valid_narrow_klass_id, "not reversible");
132
133 #ifdef AARCH64
134 // On aarch64, we never expect a shift value > 0 in standard (non-coh) mode
135 ASSERT_HERE_2(UseCompactObjectHeaders || _shift == 0, "Shift > 0 in non-coh mode?");
136 #endif
137 #undef ASSERT_HERE
138 #undef ASSERT_HERE_2
139 }
140 #endif // ASSERT
141
142 // Helper function: given current Klass Range, Base and Shift, calculate the lowest and highest values
143 // of narrowKlass we can expect.
144 void CompressedKlassPointers::calc_lowest_highest_narrow_klass_id() {
145 address lowest_possible_klass_location = _klass_range_start;
146
147 // A Klass will never be placed at the Encoding range start, since that would translate to a narrowKlass=0, which
148 // is disallowed. Note that both Metaspace and CDS prvent allocation at the first address for this reason.
149 if (lowest_possible_klass_location == _base) {
150 lowest_possible_klass_location += klass_alignment_in_bytes();
151 }
152 _lowest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(lowest_possible_klass_location - _base) >> _shift);
153
154 address highest_possible_klass_location = _klass_range_end - klass_alignment_in_bytes();
155 _highest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(highest_possible_klass_location - _base) >> _shift);
156 }
157
158 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
159 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
160 // archived heap objects.
161 void CompressedKlassPointers::initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift) {
162 if (len > max_klass_range_size()) {
163 stringStream ss;
164 ss.print("Class space size and CDS archive size combined (%zu) "
165 "exceed the maximum possible size (%zu)",
166 len, max_klass_range_size());
167 vm_exit_during_initialization(ss.base());
168 }
169
170 // Remember Klass range:
171 _klass_range_start = addr;
172 _klass_range_end = addr + len;
173
174 _base = requested_base;
175 _shift = requested_shift;
176
177 calc_lowest_highest_narrow_klass_id();
178
179 // This has already been checked for SharedBaseAddress and if this fails, it's a bug in the allocation code.
180 if (!set_klass_decode_mode()) {
181 fatal("base=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
182 p2i(_base), _shift);
183 }
184
185 DEBUG_ONLY(sanity_check_after_initialization();)
186 }
187
188 char* CompressedKlassPointers::reserve_address_space_X(uintptr_t from, uintptr_t to, size_t size, size_t alignment, bool aslr) {
189 alignment = MAX2(Metaspace::reserve_alignment(), alignment);
190 return os::attempt_reserve_memory_between((char*)from, (char*)to, size, alignment, aslr);
191 }
192
193 char* CompressedKlassPointers::reserve_address_space_for_unscaled_encoding(size_t size, bool aslr) {
194 const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
195 return reserve_address_space_X(0, unscaled_max, size, Metaspace::reserve_alignment(), aslr);
196 }
197
198 char* CompressedKlassPointers::reserve_address_space_for_zerobased_encoding(size_t size, bool aslr) {
199 const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
200 const size_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
201 return reserve_address_space_X(unscaled_max, zerobased_max, size, Metaspace::reserve_alignment(), aslr);
202 }
203
204 char* CompressedKlassPointers::reserve_address_space_for_16bit_move(size_t size, bool aslr) {
205 return reserve_address_space_X(nth_bit(32), nth_bit(48), size, nth_bit(32), aslr);
206 }
207
208 void CompressedKlassPointers::initialize(address addr, size_t len) {
209
210 if (len > max_klass_range_size()) {
211 stringStream ss;
212 ss.print("Class space size (%zu) exceeds the maximum possible size (%zu)",
213 len, max_klass_range_size());
214 vm_exit_during_initialization(ss.base());
215 }
216
217 // Remember the Klass range:
218 _klass_range_start = addr;
219 _klass_range_end = addr + len;
220
221 // Calculate Base and Shift:
222
223 if (UseCompactObjectHeaders) {
224
225 // This handles the case that we - experimentally - reduce the number of
226 // class pointer bits further, such that (shift + num bits) < 32.
227 assert(len <= (size_t)nth_bit(narrow_klass_pointer_bits() + max_shift()),
228 "klass range size exceeds encoding, len: %zu, narrow_klass_pointer_bits: %d, max_shift: %d", len, narrow_klass_pointer_bits(), max_shift());
229
230 // In compact object header mode, with 19-bit narrowKlass, we don't attempt for
231 // zero-based mode. Instead, we set the base to the start of the klass range and
232 // then try for the smallest shift possible that still covers the whole range.
233 // The reason is that we want to avoid, if possible, shifts larger than
234 // a cacheline size.
235 _base = addr;
236
237 const int log_cacheline = exact_log2(DEFAULT_CACHE_LINE_SIZE);
238 int s = max_shift();
239 while (s > log_cacheline && ((size_t)nth_bit(narrow_klass_pointer_bits() + s - 1) > len)) {
240 s--;
241 }
242 _shift = s;
243
244 } else {
245
246 // Traditional (non-compact) header mode
247 const uintptr_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
248 const uintptr_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
249
250 #ifdef AARCH64
251 // Aarch64 avoids zero-base shifted mode (_base=0 _shift>0), instead prefers
252 // non-zero-based mode with a zero shift.
253 _shift = 0;
254 address const end = addr + len;
255 _base = (end <= (address)unscaled_max) ? nullptr : addr;
256 #else
257 // We try, in order of preference:
258 // -unscaled (base=0 shift=0)
259 // -zero-based (base=0 shift>0)
260 // -nonzero-base (base>0 shift=0)
261 // Note that base>0 shift>0 should never be needed, since the klass range will
262 // never exceed 4GB.
263 address const end = addr + len;
264 if (end <= (address)unscaled_max) {
265 _base = nullptr;
266 _shift = 0;
267 } else {
268 if (end <= (address)zerobased_max) {
269 _base = nullptr;
270 _shift = max_shift();
271 } else {
272 _base = addr;
273 _shift = 0;
274 }
275 }
276 #endif // AARCH64
277 }
278
279 calc_lowest_highest_narrow_klass_id();
280
281 // Initialize klass decode mode and check compability with decode instructions
282 if (!set_klass_decode_mode()) {
283
284 // Give fatal error if this is a specified address
285 if (CompressedClassSpaceBaseAddress == (size_t)_base) {
286 vm_exit_during_initialization(
287 err_msg("CompressedClassSpaceBaseAddress=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
288 CompressedClassSpaceBaseAddress, _shift));
289 } else {
290 // If this fails, it's a bug in the allocation code.
291 fatal("CompressedClassSpaceBaseAddress=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
292 p2i(_base), _shift);
293 }
294 }
295 #ifdef ASSERT
296 sanity_check_after_initialization();
297 #endif
298 }
299
300 void CompressedKlassPointers::print_mode(outputStream* st) {
301 st->print_cr("UseCompressedClassPointers %d, UseCompactObjectHeaders %d",
302 UseCompressedClassPointers, UseCompactObjectHeaders);
303 if (UseCompressedClassPointers) {
304 st->print_cr("Narrow klass pointer bits %d, Max shift %d",
305 _narrow_klass_pointer_bits, _max_shift);
306 st->print_cr("Narrow klass base: " PTR_FORMAT ", Narrow klass shift: %d",
307 p2i(base()), shift());
308 st->print_cr("Encoding Range: " RANGE2FMT, RANGE2FMTARGS(_base, encoding_range_end()));
309 st->print_cr("Klass Range: " RANGE2FMT, RANGE2FMTARGS(_klass_range_start, _klass_range_end));
310 st->print_cr("Klass ID Range: [%u - %u) (%u)", _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id + 1,
311 _highest_valid_narrow_klass_id + 1 - _lowest_valid_narrow_klass_id);
312 if (_protection_zone_size > 0) {
313 st->print_cr("Protection zone: " RANGEFMT, RANGEFMTARGS(_base, _protection_zone_size));
314 } else {
315 st->print_cr("No protection zone.");
316 }
317 } else {
318 st->print_cr("UseCompressedClassPointers off");
319 }
320 }
321
322 // On AIX, we cannot mprotect archive space or class space since they are reserved with SystemV shm.
323 static constexpr bool can_mprotect_archive_space = NOT_AIX(true) AIX_ONLY(false);
324
325 // Protect a zone a the start of the encoding range
326 void CompressedKlassPointers::establish_protection_zone(address addr, size_t size) {
327 assert(_protection_zone_size == 0, "just once");
328 assert(addr == base(), "Protection zone not at start of encoding range?");
329 assert(size > 0 && is_aligned(size, os::vm_page_size()), "Protection zone not page sized");
330 const bool rc = can_mprotect_archive_space && os::protect_memory((char*)addr, size, os::MEM_PROT_NONE, false);
331 log_info(metaspace)("%s Narrow Klass Protection zone " RANGEFMT,
332 (rc ? "Established" : "FAILED to establish "),
333 RANGEFMTARGS(addr, size));
334 if (!rc) {
335 // If we fail to establish the protection zone, we fill it with a clear pattern to make it
336 // stick out in register values (0x50 aka 'P', repeated)
337 os::commit_memory((char*)addr, size, false);
338 memset(addr, 'P', size);
339 }
340 _protection_zone_size = size;
341 }
342
343 bool CompressedKlassPointers::is_in_protection_zone(address addr) {
344 return _protection_zone_size > 0 ?
345 (addr >= base() && addr < base() + _protection_zone_size) : false;
346 }
347
348 #endif // _LP64