| File: | compiler-rt/lib/scudo/scudo_allocator_secondary.h |
| Warning: | line 121, column 9 Value stored to 'ReservedEnd' is never read |
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| 1 | //===-- scudo_allocator_secondary.h -----------------------------*- C++ -*-===// |
| 2 | // |
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | // See https://llvm.org/LICENSE.txt for license information. |
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | // |
| 7 | //===----------------------------------------------------------------------===// |
| 8 | /// |
| 9 | /// Scudo Secondary Allocator. |
| 10 | /// This services allocation that are too large to be serviced by the Primary |
| 11 | /// Allocator. It is directly backed by the memory mapping functions of the |
| 12 | /// operating system. |
| 13 | /// |
| 14 | //===----------------------------------------------------------------------===// |
| 15 | |
| 16 | #ifndef SCUDO_ALLOCATOR_SECONDARY_H_ |
| 17 | #define SCUDO_ALLOCATOR_SECONDARY_H_ |
| 18 | |
| 19 | #ifndef SCUDO_ALLOCATOR_H_ |
| 20 | # error "This file must be included inside scudo_allocator.h." |
| 21 | #endif |
| 22 | |
| 23 | // Secondary backed allocations are standalone chunks that contain extra |
| 24 | // information stored in a LargeChunk::Header prior to the frontend's header. |
| 25 | // |
| 26 | // The secondary takes care of alignment requirements (so that it can release |
| 27 | // unnecessary pages in the rare event of larger alignments), and as such must |
| 28 | // know about the frontend's header size. |
| 29 | // |
| 30 | // Since Windows doesn't support partial releasing of a reserved memory region, |
| 31 | // we have to keep track of both the reserved and the committed memory. |
| 32 | // |
| 33 | // The resulting chunk resembles the following: |
| 34 | // |
| 35 | // +--------------------+ |
| 36 | // | Guard page(s) | |
| 37 | // +--------------------+ |
| 38 | // | Unused space* | |
| 39 | // +--------------------+ |
| 40 | // | LargeChunk::Header | |
| 41 | // +--------------------+ |
| 42 | // | {Unp,P}ackedHeader | |
| 43 | // +--------------------+ |
| 44 | // | Data (aligned) | |
| 45 | // +--------------------+ |
| 46 | // | Unused space** | |
| 47 | // +--------------------+ |
| 48 | // | Guard page(s) | |
| 49 | // +--------------------+ |
| 50 | |
| 51 | namespace LargeChunk { |
| 52 | struct Header { |
| 53 | ReservedAddressRange StoredRange; |
| 54 | uptr CommittedSize; |
| 55 | uptr Size; |
| 56 | }; |
| 57 | constexpr uptr getHeaderSize() { |
| 58 | return RoundUpTo(sizeof(Header), MinAlignment); |
| 59 | } |
| 60 | static Header *getHeader(uptr Ptr) { |
| 61 | return reinterpret_cast<Header *>(Ptr - getHeaderSize()); |
| 62 | } |
| 63 | static Header *getHeader(const void *Ptr) { |
| 64 | return getHeader(reinterpret_cast<uptr>(Ptr)); |
| 65 | } |
| 66 | } // namespace LargeChunk |
| 67 | |
| 68 | class LargeMmapAllocator { |
| 69 | public: |
| 70 | void Init() { |
| 71 | internal_memset(this, 0, sizeof(*this)); |
| 72 | } |
| 73 | |
| 74 | void *Allocate(AllocatorStats *Stats, uptr Size, uptr Alignment) { |
| 75 | const uptr UserSize = Size - Chunk::getHeaderSize(); |
| 76 | // The Scudo frontend prevents us from allocating more than |
| 77 | // MaxAllowedMallocSize, so integer overflow checks would be superfluous. |
| 78 | uptr ReservedSize = Size + LargeChunk::getHeaderSize(); |
| 79 | if (UNLIKELY(Alignment > MinAlignment)__builtin_expect(!!(Alignment > MinAlignment), 0)) |
| 80 | ReservedSize += Alignment; |
| 81 | const uptr PageSize = GetPageSizeCached(); |
| 82 | ReservedSize = RoundUpTo(ReservedSize, PageSize); |
| 83 | // Account for 2 guard pages, one before and one after the chunk. |
| 84 | ReservedSize += 2 * PageSize; |
| 85 | |
| 86 | ReservedAddressRange AddressRange; |
| 87 | uptr ReservedBeg = AddressRange.Init(ReservedSize, SecondaryAllocatorName); |
| 88 | if (UNLIKELY(ReservedBeg == ~static_cast<uptr>(0))__builtin_expect(!!(ReservedBeg == ~static_cast<uptr>(0 )), 0)) |
| 89 | return nullptr; |
| 90 | // A page-aligned pointer is assumed after that, so check it now. |
| 91 | DCHECK(IsAligned(ReservedBeg, PageSize)); |
| 92 | uptr ReservedEnd = ReservedBeg + ReservedSize; |
| 93 | // The beginning of the user area for that allocation comes after the |
| 94 | // initial guard page, and both headers. This is the pointer that has to |
| 95 | // abide by alignment requirements. |
| 96 | uptr CommittedBeg = ReservedBeg + PageSize; |
| 97 | uptr UserBeg = CommittedBeg + HeadersSize; |
| 98 | uptr UserEnd = UserBeg + UserSize; |
| 99 | uptr CommittedEnd = RoundUpTo(UserEnd, PageSize); |
| 100 | |
| 101 | // In the rare event of larger alignments, we will attempt to fit the mmap |
| 102 | // area better and unmap extraneous memory. This will also ensure that the |
| 103 | // offset and unused bytes field of the header stay small. |
| 104 | if (UNLIKELY(Alignment > MinAlignment)__builtin_expect(!!(Alignment > MinAlignment), 0)) { |
| 105 | if (!IsAligned(UserBeg, Alignment)) { |
| 106 | UserBeg = RoundUpTo(UserBeg, Alignment); |
| 107 | CommittedBeg = RoundDownTo(UserBeg - HeadersSize, PageSize); |
| 108 | const uptr NewReservedBeg = CommittedBeg - PageSize; |
| 109 | DCHECK_GE(NewReservedBeg, ReservedBeg); |
| 110 | if (!SANITIZER_WINDOWS0 && NewReservedBeg != ReservedBeg) { |
| 111 | AddressRange.Unmap(ReservedBeg, NewReservedBeg - ReservedBeg); |
| 112 | ReservedBeg = NewReservedBeg; |
| 113 | } |
| 114 | UserEnd = UserBeg + UserSize; |
| 115 | CommittedEnd = RoundUpTo(UserEnd, PageSize); |
| 116 | } |
| 117 | const uptr NewReservedEnd = CommittedEnd + PageSize; |
| 118 | DCHECK_LE(NewReservedEnd, ReservedEnd); |
| 119 | if (!SANITIZER_WINDOWS0 && NewReservedEnd != ReservedEnd) { |
| 120 | AddressRange.Unmap(NewReservedEnd, ReservedEnd - NewReservedEnd); |
| 121 | ReservedEnd = NewReservedEnd; |
Value stored to 'ReservedEnd' is never read | |
| 122 | } |
| 123 | } |
| 124 | |
| 125 | DCHECK_LE(UserEnd, CommittedEnd); |
| 126 | const uptr CommittedSize = CommittedEnd - CommittedBeg; |
| 127 | // Actually mmap the memory, preserving the guard pages on either sides. |
| 128 | CHECK_EQ(CommittedBeg, AddressRange.Map(CommittedBeg, CommittedSize))do { __sanitizer::u64 v1 = (__sanitizer::u64)((CommittedBeg)) ; __sanitizer::u64 v2 = (__sanitizer::u64)((AddressRange.Map( CommittedBeg, CommittedSize))); if (__builtin_expect(!!(!(v1 == v2)), 0)) __sanitizer::CheckFailed("/build/llvm-toolchain-snapshot-10~++20200112100611+7fa5290d5bd/compiler-rt/lib/scudo/scudo_allocator_secondary.h" , 128, "(" "(CommittedBeg)" ") " "==" " (" "(AddressRange.Map(CommittedBeg, CommittedSize))" ")", v1, v2); } while (false); |
| 129 | const uptr Ptr = UserBeg - Chunk::getHeaderSize(); |
| 130 | LargeChunk::Header *H = LargeChunk::getHeader(Ptr); |
| 131 | H->StoredRange = AddressRange; |
| 132 | H->Size = CommittedEnd - Ptr; |
| 133 | H->CommittedSize = CommittedSize; |
| 134 | |
| 135 | // The primary adds the whole class size to the stats when allocating a |
| 136 | // chunk, so we will do something similar here. But we will not account for |
| 137 | // the guard pages. |
| 138 | { |
| 139 | SpinMutexLock l(&StatsMutex); |
| 140 | Stats->Add(AllocatorStatAllocated, CommittedSize); |
| 141 | Stats->Add(AllocatorStatMapped, CommittedSize); |
| 142 | AllocatedBytes += CommittedSize; |
| 143 | if (LargestSize < CommittedSize) |
| 144 | LargestSize = CommittedSize; |
| 145 | NumberOfAllocs++; |
| 146 | } |
| 147 | |
| 148 | return reinterpret_cast<void *>(Ptr); |
| 149 | } |
| 150 | |
| 151 | void Deallocate(AllocatorStats *Stats, void *Ptr) { |
| 152 | LargeChunk::Header *H = LargeChunk::getHeader(Ptr); |
| 153 | // Since we're unmapping the entirety of where the ReservedAddressRange |
| 154 | // actually is, copy onto the stack. |
| 155 | ReservedAddressRange AddressRange = H->StoredRange; |
| 156 | const uptr Size = H->CommittedSize; |
| 157 | { |
| 158 | SpinMutexLock l(&StatsMutex); |
| 159 | Stats->Sub(AllocatorStatAllocated, Size); |
| 160 | Stats->Sub(AllocatorStatMapped, Size); |
| 161 | FreedBytes += Size; |
| 162 | NumberOfFrees++; |
| 163 | } |
| 164 | AddressRange.Unmap(reinterpret_cast<uptr>(AddressRange.base()), |
| 165 | AddressRange.size()); |
| 166 | } |
| 167 | |
| 168 | static uptr GetActuallyAllocatedSize(void *Ptr) { |
| 169 | return LargeChunk::getHeader(Ptr)->Size; |
| 170 | } |
| 171 | |
| 172 | void PrintStats() { |
| 173 | Printf("Stats: LargeMmapAllocator: allocated %zd times (%zd K), " |
| 174 | "freed %zd times (%zd K), remains %zd (%zd K) max %zd M\n", |
| 175 | NumberOfAllocs, AllocatedBytes >> 10, NumberOfFrees, |
| 176 | FreedBytes >> 10, NumberOfAllocs - NumberOfFrees, |
| 177 | (AllocatedBytes - FreedBytes) >> 10, LargestSize >> 20); |
| 178 | } |
| 179 | |
| 180 | private: |
| 181 | static constexpr uptr HeadersSize = |
| 182 | LargeChunk::getHeaderSize() + Chunk::getHeaderSize(); |
| 183 | |
| 184 | StaticSpinMutex StatsMutex; |
| 185 | u32 NumberOfAllocs; |
| 186 | u32 NumberOfFrees; |
| 187 | uptr AllocatedBytes; |
| 188 | uptr FreedBytes; |
| 189 | uptr LargestSize; |
| 190 | }; |
| 191 | |
| 192 | #endif // SCUDO_ALLOCATOR_SECONDARY_H_ |