< prev index next > src/hotspot/share/oops/compressedKlass.cpp
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*/
#include "precompiled.hpp"
#include "logging/log.hpp"
#include "memory/metaspace.hpp"
- #include "oops/compressedKlass.hpp"
+ #include "oops/klass.hpp"
+ #include "oops/compressedKlass.inline.hpp"
#include "runtime/globals.hpp"
+ #include "runtime/java.hpp"
#include "runtime/os.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/ostream.hpp"
- address CompressedKlassPointers::_base = nullptr;
- int CompressedKlassPointers::_shift = 0;
- size_t CompressedKlassPointers::_range = 0;
+ int CompressedKlassPointers::_tiny_cp = -1;
+ int CompressedKlassPointers::_narrow_klass_pointer_bits = -1;
+ int CompressedKlassPointers::_max_shift = -1;
+ #ifdef ASSERT
+ address CompressedKlassPointers::_klass_range_start = (address)-1;
+ address CompressedKlassPointers::_klass_range_end = (address)-1;
+ narrowKlass CompressedKlassPointers::_lowest_valid_narrow_klass_id = (narrowKlass)-1;
+ narrowKlass CompressedKlassPointers::_highest_valid_narrow_klass_id = (narrowKlass)-1;
+ #endif
+
+ address CompressedKlassPointers::_base = (address)-1;
+ int CompressedKlassPointers::_shift = -1;
+ size_t CompressedKlassPointers::_range = (size_t)-1;
+
+ // The maximum allowed length of the Klass range (the address range engulfing
+ // CDS + class space) must not exceed 32-bit.
+ // There is a theoretical limit of: must not exceed the size of a fully-shifted
+ // narrow Klass pointer, which would be 32 + 3 = 35 bits in legacy mode;
+ // however, keeping this size below 32-bit allows us to use decoding techniques
+ // like 16-bit moves into the third quadrant on some architectures, and keeps
+ // the code less complex. 32-bit have always been enough for CDS+class space.
+ static constexpr size_t max_klass_range_size = 4 * G;
#ifdef _LP64
- #ifdef ASSERT
- void CompressedKlassPointers::assert_is_valid_encoding(address addr, size_t len, address base, int shift) {
- assert(base + nth_bit(32 + shift) >= addr + len, "Encoding (base=" PTR_FORMAT ", shift=%d) does not "
- "fully cover the class range " PTR_FORMAT "-" PTR_FORMAT, p2i(base), shift, p2i(addr), p2i(addr + len));
+ void CompressedKlassPointers::pre_initialize() {
+ if (UseCompactObjectHeaders) {
+ _tiny_cp = 1;
+ _narrow_klass_pointer_bits = narrow_klass_pointer_bits_tinycp;
+ _max_shift = max_shift_tinycp;
+ } else {
+ _tiny_cp = 0;
+ _narrow_klass_pointer_bits = narrow_klass_pointer_bits_legacy;
+ _max_shift = max_shift_legacy;
+ }
}
+
+ #ifdef ASSERT
+ void CompressedKlassPointers::sanity_check_after_initialization() {
+ // In expectation of an assert, prepare condensed info to be printed with the assert.
+ char tmp[256];
+ os::snprintf(tmp, sizeof(tmp), PTR_FORMAT " " PTR_FORMAT " " PTR_FORMAT " %d " SIZE_FORMAT " %u %u",
+ p2i(_klass_range_start), p2i(_klass_range_end), p2i(_base), _shift, _range,
+ _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id);
+ #define ASSERT_HERE(cond) assert(cond, " (%s)", tmp);
+ #define ASSERT_HERE_2(cond, msg) assert(cond, msg " (%s)", tmp);
+
+ // There is no technical reason preventing us from using other klass pointer bit lengths,
+ // but it should be a deliberate choice
+ ASSERT_HERE(_narrow_klass_pointer_bits == 32 || _narrow_klass_pointer_bits == 22);
+
+ // All values must be inited
+ ASSERT_HERE(_max_shift != -1);
+ ASSERT_HERE(_klass_range_start != (address)-1);
+ ASSERT_HERE(_klass_range_end != (address)-1);
+ ASSERT_HERE(_lowest_valid_narrow_klass_id != (narrowKlass)-1);
+ ASSERT_HERE(_base != (address)-1);
+ ASSERT_HERE(_shift != -1);
+ ASSERT_HERE(_range != (size_t)-1);
+
+ const size_t klab = klass_alignment_in_bytes();
+ ASSERT_HERE(klab >= sizeof(uint64_t) && klab <= K);
+
+ // Check that Klass range is fully engulfed in the encoding range
+ ASSERT_HERE(_klass_range_end > _klass_range_start);
+
+ const address encoding_end = _base + nth_bit(narrow_klass_pointer_bits() + _shift);
+ ASSERT_HERE_2(_klass_range_start >= _base && _klass_range_end <= encoding_end,
+ "Resulting encoding range does not fully cover the class range");
+
+ // Check that Klass range is aligned to Klass alignment. That should never be an issue since we mmap the
+ // relevant regions and klass alignment - tied to smallest metachunk size of 1K - will always be smaller
+ // than smallest page size of 4K.
+ ASSERT_HERE_2(is_aligned(_klass_range_start, klab) && is_aligned(_klass_range_end, klab),
+ "Klass range must start at a properly aligned address");
+
+ // Check that lowest and highest possible narrowKlass values make sense
+ ASSERT_HERE_2(_lowest_valid_narrow_klass_id > 0, "Null is not a valid narrowKlass");
+ ASSERT_HERE(_highest_valid_narrow_klass_id > _lowest_valid_narrow_klass_id);
+
+ Klass* k1 = decode_not_null_without_asserts(_lowest_valid_narrow_klass_id, _base, _shift);
+ ASSERT_HERE_2((address)k1 == _klass_range_start + klab, "Not lowest");
+ narrowKlass nk1 = encode_not_null_without_asserts(k1, _base, _shift);
+ ASSERT_HERE_2(nk1 == _lowest_valid_narrow_klass_id, "not reversible");
+
+ Klass* k2 = decode_not_null_without_asserts(_highest_valid_narrow_klass_id, _base, _shift);
+ // _highest_valid_narrow_klass_id must be decoded to the highest theoretically possible
+ // valid Klass* position in range, if we assume minimal Klass size
+ ASSERT_HERE((address)k2 < _klass_range_end);
+ ASSERT_HERE_2(align_up(((address)k2 + sizeof(Klass)), klab) >= _klass_range_end, "Not highest");
+ narrowKlass nk2 = encode_not_null_without_asserts(k2, _base, _shift);
+ ASSERT_HERE_2(nk2 == _highest_valid_narrow_klass_id, "not reversible");
+
+ #ifdef AARCH64
+ // On aarch64, we never expect a shift value > 0 in legacy mode
+ ASSERT_HERE_2(tiny_classpointer_mode() || _shift == 0, "Shift > 0 in legacy mode?");
#endif
+ #undef ASSERT_HERE
+ #undef ASSERT_HERE_2
+ }
+
+ void CompressedKlassPointers::calc_lowest_highest_narrow_klass_id() {
+ // Given a Klass range, calculate lowest and highest narrowKlass.
+ const size_t klab = klass_alignment_in_bytes();
+ // Note that 0 is not a valid narrowKlass, and Metaspace prevents us for that reason from allocating at
+ // the very start of class space. So the very first valid Klass position is start-of-range + klab.
+ _lowest_valid_narrow_klass_id =
+ (narrowKlass) (((uintptr_t)(_klass_range_start - _base) + klab) >> _shift);
+ address highest_possible_klass = align_down(_klass_range_end - sizeof(Klass), klab);
+ _highest_valid_narrow_klass_id = (narrowKlass) ((uintptr_t)(highest_possible_klass - _base) >> _shift);
+ }
+ #endif // ASSERT
// Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
// set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
// archived heap objects.
void CompressedKlassPointers::initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift) {
address const end = addr + len;
- const int narrow_klasspointer_bits = sizeof(narrowKlass) * 8;
- const size_t encoding_range_size = nth_bit(narrow_klasspointer_bits + requested_shift);
+ if (len > max_klass_range_size) {
+ // Class space size is limited to 3G. This can theoretically happen if the CDS archive
+ // is larger than 1G and class space size is set to the maximum possible 3G.
+ vm_exit_during_initialization("Sum of CDS archive size and class space size exceed 4 GB");
+ }
+
+ const size_t encoding_range_size = nth_bit(narrow_klass_pointer_bits() + requested_shift);
address encoding_range_end = requested_base + encoding_range_size;
// Note: it would be technically valid for the encoding base to precede the start of the Klass range. But we only call
// this function from CDS, and therefore know this to be true.
assert(requested_base == addr, "Invalid requested base");
- assert(encoding_range_end >= end, "Encoding does not cover the full Klass range");
_base = requested_base;
_shift = requested_shift;
_range = encoding_range_size;
- DEBUG_ONLY(assert_is_valid_encoding(addr, len, _base, _shift);)
+ #ifdef ASSERT
+ _klass_range_start = addr;
+ _klass_range_end = addr + len;
+ calc_lowest_highest_narrow_klass_id();
+ sanity_check_after_initialization();
+ #endif
+
+ DEBUG_ONLY(sanity_check_after_initialization();)
}
char* CompressedKlassPointers::reserve_address_space_X(uintptr_t from, uintptr_t to, size_t size, size_t alignment, bool aslr) {
alignment = MAX2(Metaspace::reserve_alignment(), alignment);
return os::attempt_reserve_memory_between((char*)from, (char*)to, size, alignment, aslr);
}
char* CompressedKlassPointers::reserve_address_space_for_unscaled_encoding(size_t size, bool aslr) {
- return reserve_address_space_X(0, nth_bit(32), size, Metaspace::reserve_alignment(), aslr);
+ const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
+ return reserve_address_space_X(0, unscaled_max, size, Metaspace::reserve_alignment(), aslr);
}
char* CompressedKlassPointers::reserve_address_space_for_zerobased_encoding(size_t size, bool aslr) {
- return reserve_address_space_X(nth_bit(32), nth_bit(32 + LogKlassAlignmentInBytes), size, Metaspace::reserve_alignment(), aslr);
+ const size_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
+ const size_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
+ return reserve_address_space_X(unscaled_max, zerobased_max, size, Metaspace::reserve_alignment(), aslr);
}
char* CompressedKlassPointers::reserve_address_space_for_16bit_move(size_t size, bool aslr) {
return reserve_address_space_X(nth_bit(32), nth_bit(48), size, nth_bit(32), aslr);
}
- #if !defined(AARCH64) || defined(ZERO)
- // On aarch64 we have an own version; all other platforms use the default version
void CompressedKlassPointers::initialize(address addr, size_t len) {
- // The default version of this code tries, in order of preference:
- // -unscaled (base=0 shift=0)
- // -zero-based (base=0 shift>0)
- // -nonzero-base (base>0 shift=0)
- // Note that base>0 shift>0 should never be needed, since the klass range will
- // never exceed 4GB.
- constexpr uintptr_t unscaled_max = nth_bit(32);
- assert(len <= unscaled_max, "Klass range larger than 32 bits?");
- constexpr uintptr_t zerobased_max = nth_bit(32 + LogKlassAlignmentInBytes);
+ if (len > max_klass_range_size) {
+ // Class space size is limited to 3G. This can theoretically happen if the CDS archive
+ // is larger than 1G and class space size is set to the maximum possible 3G.
+ vm_exit_during_initialization("Sum of CDS archive size and class space size exceed 4 GB");
+ }
+
+ // Give CPU a shot at a specialized init sequence
+ #ifndef ZERO
+ if (pd_initialize(addr, len)) {
+ return;
+ }
+ #endif
+
+ if (tiny_classpointer_mode()) {
+
+ // This handles the case that we - experimentally - reduce the number of
+ // class pointer bits further, such that (shift + num bits) < 32.
+ assert(len <= (size_t)nth_bit(narrow_klass_pointer_bits() + max_shift()),
+ "klass range size exceeds encoding");
+
+ // In tiny classpointer mode, we don't attempt for zero-based mode.
+ // Instead, we set the base to the start of the klass range and then try
+ // for the smallest shift possible that still covers the whole range.
+ // The reason is that we want to avoid, if possible, shifts larger than
+ // a cacheline size.
+ _base = addr;
+ _range = len;
+
+ if (TinyClassPointerShift != 0) {
+ _shift = TinyClassPointerShift;
+ } else {
+ constexpr int log_cacheline = 6;
+ int s = max_shift();
+ while (s > log_cacheline && ((size_t)nth_bit(narrow_klass_pointer_bits() + s - 1) > len)) {
+ s--;
+ }
+ _shift = s;
+ }
- address const end = addr + len;
- if (end <= (address)unscaled_max) {
- _base = nullptr;
- _shift = 0;
} else {
- if (end <= (address)zerobased_max) {
+
+ // In legacy mode, we try, in order of preference:
+ // -unscaled (base=0 shift=0)
+ // -zero-based (base=0 shift>0)
+ // -nonzero-base (base>0 shift=0)
+ // Note that base>0 shift>0 should never be needed, since the klass range will
+ // never exceed 4GB.
+ const uintptr_t unscaled_max = nth_bit(narrow_klass_pointer_bits());
+ const uintptr_t zerobased_max = nth_bit(narrow_klass_pointer_bits() + max_shift());
+
+ address const end = addr + len;
+ if (end <= (address)unscaled_max) {
_base = nullptr;
- _shift = LogKlassAlignmentInBytes;
- } else {
- _base = addr;
_shift = 0;
+ } else {
+ if (end <= (address)zerobased_max) {
+ _base = nullptr;
+ _shift = max_shift();
+ } else {
+ _base = addr;
+ _shift = 0;
+ }
}
+ _range = end - _base;
+
}
- _range = end - _base;
- DEBUG_ONLY(assert_is_valid_encoding(addr, len, _base, _shift);)
+ #ifdef ASSERT
+ _klass_range_start = addr;
+ _klass_range_end = addr + len;
+ calc_lowest_highest_narrow_klass_id();
+ sanity_check_after_initialization();
+ #endif
}
- #endif // !AARCH64 || ZERO
void CompressedKlassPointers::print_mode(outputStream* st) {
+ st->print_cr("UseCompressedClassPointers %d, UseCompactObjectHeaders %d, "
+ "narrow klass pointer bits %d, max shift %d",
+ UseCompressedClassPointers, UseCompactObjectHeaders,
+ _narrow_klass_pointer_bits, _max_shift);
+ if (_base == (address)-1) {
+ st->print_cr("Narrow klass encoding not initialized");
+ return;
+ }
st->print_cr("Narrow klass base: " PTR_FORMAT ", Narrow klass shift: %d, "
"Narrow klass range: " SIZE_FORMAT_X, p2i(base()), shift(),
range());
+ #ifdef ASSERT
+ st->print_cr("Klass range: [" PTR_FORMAT "," PTR_FORMAT ")",
+ p2i(_klass_range_start), p2i(_klass_range_end));
+ st->print_cr("Lowest valid nklass id: %u Highest valid nklass id: %u",
+ _lowest_valid_narrow_klass_id, _highest_valid_narrow_klass_id);
+ #endif
}
#endif // _LP64
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