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