src/llvm/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/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