1 //===-- ASanStackFrameLayout.cpp - helper for AddressSanitizer ------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // Definition of ComputeASanStackFrameLayout (see ASanStackFrameLayout.h). 11 // 12 //===----------------------------------------------------------------------===// 13 #include "llvm/Transforms/Utils/ASanStackFrameLayout.h" 14 #include "llvm/ADT/SmallString.h" 15 #include "llvm/IR/DebugInfo.h" 16 #include "llvm/Support/MathExtras.h" 17 #include "llvm/Support/ScopedPrinter.h" 18 #include "llvm/Support/raw_ostream.h" 19 #include <algorithm> 20 21 namespace llvm { 22 23 // We sort the stack variables by alignment (largest first) to minimize 24 // unnecessary large gaps due to alignment. 25 // It is tempting to also sort variables by size so that larger variables 26 // have larger redzones at both ends. But reordering will make report analysis 27 // harder, especially when temporary unnamed variables are present. 28 // So, until we can provide more information (type, line number, etc) 29 // for the stack variables we avoid reordering them too much. 30 static inline bool CompareVars(const ASanStackVariableDescription &a, 31 const ASanStackVariableDescription &b) { 32 return a.Alignment > b.Alignment; 33 } 34 35 // We also force minimal alignment for all vars to kMinAlignment so that vars 36 // with e.g. alignment 1 and alignment 16 do not get reordered by CompareVars. 37 static const size_t kMinAlignment = 16; 38 39 // The larger the variable Size the larger is the redzone. 40 // The resulting frame size is a multiple of Alignment. 41 static size_t VarAndRedzoneSize(size_t Size, size_t Alignment) { 42 size_t Res = 0; 43 if (Size <= 4) Res = 16; 44 else if (Size <= 16) Res = 32; 45 else if (Size <= 128) Res = Size + 32; 46 else if (Size <= 512) Res = Size + 64; 47 else if (Size <= 4096) Res = Size + 128; 48 else Res = Size + 256; 49 return alignTo(Res, Alignment); 50 } 51 52 ASanStackFrameLayout 53 ComputeASanStackFrameLayout(SmallVectorImpl<ASanStackVariableDescription> &Vars, 54 size_t Granularity, size_t MinHeaderSize) { 55 assert(Granularity >= 8 && Granularity <= 64 && 56 (Granularity & (Granularity - 1)) == 0); 57 assert(MinHeaderSize >= 16 && (MinHeaderSize & (MinHeaderSize - 1)) == 0 && 58 MinHeaderSize >= Granularity); 59 const size_t NumVars = Vars.size(); 60 assert(NumVars > 0); 61 for (size_t i = 0; i < NumVars; i++) 62 Vars[i].Alignment = std::max(Vars[i].Alignment, kMinAlignment); 63 64 std::stable_sort(Vars.begin(), Vars.end(), CompareVars); 65 66 ASanStackFrameLayout Layout; 67 Layout.Granularity = Granularity; 68 Layout.FrameAlignment = std::max(Granularity, Vars[0].Alignment); 69 size_t Offset = std::max(std::max(MinHeaderSize, Granularity), 70 Vars[0].Alignment); 71 assert((Offset % Granularity) == 0); 72 for (size_t i = 0; i < NumVars; i++) { 73 bool IsLast = i == NumVars - 1; 74 size_t Alignment = std::max(Granularity, Vars[i].Alignment); 75 (void)Alignment; // Used only in asserts. 76 size_t Size = Vars[i].Size; 77 assert((Alignment & (Alignment - 1)) == 0); 78 assert(Layout.FrameAlignment >= Alignment); 79 assert((Offset % Alignment) == 0); 80 assert(Size > 0); 81 size_t NextAlignment = IsLast ? Granularity 82 : std::max(Granularity, Vars[i + 1].Alignment); 83 size_t SizeWithRedzone = VarAndRedzoneSize(Size, NextAlignment); 84 Vars[i].Offset = Offset; 85 Offset += SizeWithRedzone; 86 } 87 if (Offset % MinHeaderSize) { 88 Offset += MinHeaderSize - (Offset % MinHeaderSize); 89 } 90 Layout.FrameSize = Offset; 91 assert((Layout.FrameSize % MinHeaderSize) == 0); 92 return Layout; 93 } 94 95 SmallString<64> ComputeASanStackFrameDescription( 96 const SmallVectorImpl<ASanStackVariableDescription> &Vars) { 97 SmallString<2048> StackDescriptionStorage; 98 raw_svector_ostream StackDescription(StackDescriptionStorage); 99 StackDescription << Vars.size(); 100 101 for (const auto &Var : Vars) { 102 std::string Name = Var.Name; 103 if (Var.Line) { 104 Name += ":"; 105 Name += to_string(Var.Line); 106 } 107 StackDescription << " " << Var.Offset << " " << Var.Size << " " 108 << Name.size() << " " << Name; 109 } 110 return StackDescription.str(); 111 } 112 113 SmallVector<uint8_t, 64> 114 GetShadowBytes(const SmallVectorImpl<ASanStackVariableDescription> &Vars, 115 const ASanStackFrameLayout &Layout) { 116 assert(Vars.size() > 0); 117 SmallVector<uint8_t, 64> SB; 118 SB.clear(); 119 const size_t Granularity = Layout.Granularity; 120 SB.resize(Vars[0].Offset / Granularity, kAsanStackLeftRedzoneMagic); 121 for (const auto &Var : Vars) { 122 SB.resize(Var.Offset / Granularity, kAsanStackMidRedzoneMagic); 123 124 SB.resize(SB.size() + Var.Size / Granularity, 0); 125 if (Var.Size % Granularity) 126 SB.push_back(Var.Size % Granularity); 127 } 128 SB.resize(Layout.FrameSize / Granularity, kAsanStackRightRedzoneMagic); 129 return SB; 130 } 131 132 SmallVector<uint8_t, 64> GetShadowBytesAfterScope( 133 const SmallVectorImpl<ASanStackVariableDescription> &Vars, 134 const ASanStackFrameLayout &Layout) { 135 SmallVector<uint8_t, 64> SB = GetShadowBytes(Vars, Layout); 136 const size_t Granularity = Layout.Granularity; 137 138 for (const auto &Var : Vars) { 139 assert(Var.LifetimeSize <= Var.Size); 140 const size_t LifetimeShadowSize = 141 (Var.LifetimeSize + Granularity - 1) / Granularity; 142 const size_t Offset = Var.Offset / Granularity; 143 std::fill(SB.begin() + Offset, SB.begin() + Offset + LifetimeShadowSize, 144 kAsanStackUseAfterScopeMagic); 145 } 146 147 return SB; 148 } 149 150 } // llvm namespace 151