llvm/lib/Transforms/Utils/ASanStackFrameLayout.cpp

   1 //===-- ASanStackFrameLayout.cpp - helper for AddressSanitizer ------------===//
   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 // Definition of ComputeASanStackFrameLayout (see ASanStackFrameLayout.h).
  10 //
  11 //===----------------------------------------------------------------------===//
  12 #include "llvm/Transforms/Utils/ASanStackFrameLayout.h"
  13 #include "llvm/ADT/SmallString.h"
  14 #include "llvm/Support/MathExtras.h"
  15 #include "llvm/Support/ScopedPrinter.h"
  16 #include "llvm/Support/raw_ostream.h"
  17 #include <algorithm>
  18
  19 namespace llvm {
  20
  21 // We sort the stack variables by alignment (largest first) to minimize
  22 // unnecessary large gaps due to alignment.
  23 // It is tempting to also sort variables by size so that larger variables
  24 // have larger redzones at both ends. But reordering will make report analysis
  25 // harder, especially when temporary unnamed variables are present.
  26 // So, until we can provide more information (type, line number, etc)
  27 // for the stack variables we avoid reordering them too much.
  28 static inline bool CompareVars(const ASanStackVariableDescription &a,
  29                                const ASanStackVariableDescription &b) {
  30   return a.Alignment > b.Alignment;
  31 }
  32
  33 // We also force minimal alignment for all vars to kMinAlignment so that vars
  34 // with e.g. alignment 1 and alignment 16 do not get reordered by CompareVars.
  35 static const uint64_t kMinAlignment = 16;
  36
  37 // We want to add a full redzone after every variable.
  38 // The larger the variable Size the larger is the redzone.
  39 // The resulting frame size is a multiple of Alignment.
  40 static uint64_t VarAndRedzoneSize(uint64_t Size, uint64_t Granularity,
  41                                   uint64_t Alignment) {
  42   uint64_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(std::max(Res, 2 * Granularity), Alignment);
  50 }
  51
  52 ASanStackFrameLayout
  53 ComputeASanStackFrameLayout(SmallVectorImpl<ASanStackVariableDescription> &Vars,
  54                             uint64_t Granularity, uint64_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   llvm::stable_sort(Vars, CompareVars);
  65
  66   ASanStackFrameLayout Layout;
  67   Layout.Granularity = Granularity;
  68   Layout.FrameAlignment = std::max(Granularity, Vars[0].Alignment);
  69   uint64_t Offset =
  70       std::max(std::max(MinHeaderSize, Granularity), Vars[0].Alignment);
  71   assert((Offset % Granularity) == 0);
  72   for (size_t i = 0; i < NumVars; i++) {
  73     bool IsLast = i == NumVars - 1;
  74     uint64_t Alignment = std::max(Granularity, Vars[i].Alignment);
  75     (void)Alignment;  // Used only in asserts.
  76     uint64_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     uint64_t NextAlignment =
  82         IsLast ? Granularity : std::max(Granularity, Vars[i + 1].Alignment);
  83     uint64_t SizeWithRedzone =
  84         VarAndRedzoneSize(Size, Granularity, NextAlignment);
  85     Vars[i].Offset = Offset;
  86     Offset += SizeWithRedzone;
  87   }
  88   if (Offset % MinHeaderSize) {
  89     Offset += MinHeaderSize - (Offset % MinHeaderSize);
  90   }
  91   Layout.FrameSize = Offset;
  92   assert((Layout.FrameSize % MinHeaderSize) == 0);
  93   return Layout;
  94 }
  95
  96 SmallString<64> ComputeASanStackFrameDescription(
  97     const SmallVectorImpl<ASanStackVariableDescription> &Vars) {
  98   SmallString<2048> StackDescriptionStorage;
  99   raw_svector_ostream StackDescription(StackDescriptionStorage);
 100   StackDescription << Vars.size();
 101
 102   for (const auto &Var : Vars) {
 103     std::string Name = Var.Name;
 104     if (Var.Line) {
 105       Name += ":";
 106       Name += to_string(Var.Line);
 107     }
 108     StackDescription << " " << Var.Offset << " " << Var.Size << " "
 109                      << Name.size() << " " << Name;
 110   }
 111   return StackDescription.str();
 112 }
 113
 114 SmallVector<uint8_t, 64>
 115 GetShadowBytes(const SmallVectorImpl<ASanStackVariableDescription> &Vars,
 116                const ASanStackFrameLayout &Layout) {
 117   assert(Vars.size() > 0);
 118   SmallVector<uint8_t, 64> SB;
 119   SB.clear();
 120   const uint64_t Granularity = Layout.Granularity;
 121   SB.resize(Vars[0].Offset / Granularity, kAsanStackLeftRedzoneMagic);
 122   for (const auto &Var : Vars) {
 123     SB.resize(Var.Offset / Granularity, kAsanStackMidRedzoneMagic);
 124
 125     SB.resize(SB.size() + Var.Size / Granularity, 0);
 126     if (Var.Size % Granularity)
 127       SB.push_back(Var.Size % Granularity);
 128   }
 129   SB.resize(Layout.FrameSize / Granularity, kAsanStackRightRedzoneMagic);
 130   return SB;
 131 }
 132
 133 SmallVector<uint8_t, 64> GetShadowBytesAfterScope(
 134     const SmallVectorImpl<ASanStackVariableDescription> &Vars,
 135     const ASanStackFrameLayout &Layout) {
 136   SmallVector<uint8_t, 64> SB = GetShadowBytes(Vars, Layout);
 137   const uint64_t Granularity = Layout.Granularity;
 138
 139   for (const auto &Var : Vars) {
 140     assert(Var.LifetimeSize <= Var.Size);
 141     const uint64_t LifetimeShadowSize =
 142         (Var.LifetimeSize + Granularity - 1) / Granularity;
 143     const uint64_t Offset = Var.Offset / Granularity;
 144     std::fill(SB.begin() + Offset, SB.begin() + Offset + LifetimeShadowSize,
 145               kAsanStackUseAfterScopeMagic);
 146   }
 147
 148   return SB;
 149 }
 150
 151 } // llvm namespace