lib/Transforms/Utils/ASanStackFrameLayout.cpp

   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