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/Support/raw_ostream.h" 16 #include <algorithm> 17 18 namespace llvm { 19 20 // We sort the stack variables by alignment (largest first) to minimize 21 // unnecessary large gaps due to alignment. 22 // It is tempting to also sort variables by size so that larger variables 23 // have larger redzones at both ends. But reordering will make report analysis 24 // harder, especially when temporary unnamed variables are present. 25 // So, until we can provide more information (type, line number, etc) 26 // for the stack variables we avoid reordering them too much. 27 static inline bool CompareVars(const ASanStackVariableDescription &a, 28 const ASanStackVariableDescription &b) { 29 return a.Alignment > b.Alignment; 30 } 31 32 // We also force minimal alignment for all vars to kMinAlignment so that vars 33 // with e.g. alignment 1 and alignment 16 do not get reordered by CompareVars. 34 static const size_t kMinAlignment = 16; 35 36 static size_t RoundUpTo(size_t X, size_t RoundTo) { 37 assert((RoundTo & (RoundTo - 1)) == 0); 38 return (X + RoundTo - 1) & ~(RoundTo - 1); 39 } 40 41 // The larger the variable Size the larger is the redzone. 42 // The resulting frame size is a multiple of Alignment. 43 static size_t VarAndRedzoneSize(size_t Size, size_t Alignment) { 44 size_t Res = 0; 45 if (Size <= 4) Res = 16; 46 else if (Size <= 16) Res = 32; 47 else if (Size <= 128) Res = Size + 32; 48 else if (Size <= 512) Res = Size + 64; 49 else if (Size <= 4096) Res = Size + 128; 50 else Res = Size + 256; 51 return RoundUpTo(Res, Alignment); 52 } 53 54 void 55 ComputeASanStackFrameLayout(SmallVectorImpl<ASanStackVariableDescription> &Vars, 56 size_t Granularity, size_t MinHeaderSize, 57 ASanStackFrameLayout *Layout) { 58 assert(Granularity >= 8 && Granularity <= 64 && 59 (Granularity & (Granularity - 1)) == 0); 60 assert(MinHeaderSize >= 16 && (MinHeaderSize & (MinHeaderSize - 1)) == 0 && 61 MinHeaderSize >= Granularity); 62 size_t NumVars = Vars.size(); 63 assert(NumVars > 0); 64 for (size_t i = 0; i < NumVars; i++) 65 Vars[i].Alignment = std::max(Vars[i].Alignment, kMinAlignment); 66 67 std::stable_sort(Vars.begin(), Vars.end(), CompareVars); 68 SmallString<2048> StackDescriptionStorage; 69 raw_svector_ostream StackDescription(StackDescriptionStorage); 70 StackDescription << NumVars; 71 Layout->FrameAlignment = std::max(Granularity, Vars[0].Alignment); 72 SmallVector<uint8_t, 64> &SB(Layout->ShadowBytes); 73 SB.clear(); 74 size_t Offset = std::max(std::max(MinHeaderSize, Granularity), 75 Vars[0].Alignment); 76 assert((Offset % Granularity) == 0); 77 SB.insert(SB.end(), Offset / Granularity, kAsanStackLeftRedzoneMagic); 78 for (size_t i = 0; i < NumVars; i++) { 79 bool IsLast = i == NumVars - 1; 80 size_t Alignment = std::max(Granularity, Vars[i].Alignment); 81 (void)Alignment; // Used only in asserts. 82 size_t Size = Vars[i].Size; 83 const char *Name = Vars[i].Name; 84 assert((Alignment & (Alignment - 1)) == 0); 85 assert(Layout->FrameAlignment >= Alignment); 86 assert((Offset % Alignment) == 0); 87 assert(Size > 0); 88 StackDescription << " " << Offset << " " << Size << " " << strlen(Name) 89 << " " << Name; 90 size_t NextAlignment = IsLast ? Granularity 91 : std::max(Granularity, Vars[i + 1].Alignment); 92 size_t SizeWithRedzone = VarAndRedzoneSize(Vars[i].Size, NextAlignment); 93 SB.insert(SB.end(), Size / Granularity, 0); 94 if (Size % Granularity) 95 SB.insert(SB.end(), Size % Granularity); 96 SB.insert(SB.end(), (SizeWithRedzone - Size) / Granularity, 97 IsLast ? kAsanStackRightRedzoneMagic 98 : kAsanStackMidRedzoneMagic); 99 Vars[i].Offset = Offset; 100 Offset += SizeWithRedzone; 101 } 102 if (Offset % MinHeaderSize) { 103 size_t ExtraRedzone = MinHeaderSize - (Offset % MinHeaderSize); 104 SB.insert(SB.end(), ExtraRedzone / Granularity, 105 kAsanStackRightRedzoneMagic); 106 Offset += ExtraRedzone; 107 } 108 Layout->DescriptionString = StackDescription.str(); 109 Layout->FrameSize = Offset; 110 assert((Layout->FrameSize % MinHeaderSize) == 0); 111 assert(Layout->FrameSize / Granularity == Layout->ShadowBytes.size()); 112 } 113 114 } // llvm namespace 115
