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https://github.com/dart-lang/sdk
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a2ab7ccea4
FinalizeHash(hash) was trying to avoid UB in expression 1 << 32 by casting 1 to uintptr_t. This type however is not wide enough on 32-bit platforms. Instead just use explicit comparison hashbits < kBitsPerInt32 to avoid overflow in left shift. This bug went unnoticed for a while because it the only place where we call FinalizeHash(hash) is in the snapshot profile writer code and it only triggers when gen_snapshot is a 32-bit binary - which is only true on Windows, as Mac and Linux seem to use simarm_x64 configuration instead. This UB was explicitly affecting the code behavior because C++ compiler would either optimize out or change behavior of any code that consumed value produced by FinalizeHash(hash). Fixes https://github.com/flutter/flutter/issues/97764 TEST=vm/cc/DirectChainedHashMap Change-Id: I39f2b09e7516c875b765e5a065d1c1331f89fa33 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/250741 Commit-Queue: Slava Egorov <vegorov@google.com> Reviewed-by: Daco Harkes <dacoharkes@google.com>
42 lines
1 KiB
C++
42 lines
1 KiB
C++
// Copyright (c) 2018, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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#ifndef RUNTIME_VM_HASH_H_
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#define RUNTIME_VM_HASH_H_
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#include "platform/globals.h"
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namespace dart {
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inline uint32_t CombineHashes(uint32_t hash, uint32_t other_hash) {
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hash += other_hash;
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hash += hash << 10;
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hash ^= hash >> 6; // Logical shift, unsigned hash.
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return hash;
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}
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inline uint32_t FinalizeHash(uint32_t hash, intptr_t hashbits = kBitsPerInt32) {
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hash += hash << 3;
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hash ^= hash >> 11; // Logical shift, unsigned hash.
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hash += hash << 15;
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if (hashbits < kBitsPerInt32) {
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hash &= (static_cast<uint32_t>(1) << hashbits) - 1;
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}
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return (hash == 0) ? 1 : hash;
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}
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inline uint32_t HashBytes(const uint8_t* bytes, intptr_t size) {
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uint32_t hash = size;
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while (size > 0) {
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hash = CombineHashes(hash, *bytes);
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bytes++;
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size--;
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}
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return hash;
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}
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} // namespace dart
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#endif // RUNTIME_VM_HASH_H_
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