152 lines · 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-exception6//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 19namespace llvm {20 21// We sort the stack variables by alignment (largest first) to minimize22// unnecessary large gaps due to alignment.23// It is tempting to also sort variables by size so that larger variables24// have larger redzones at both ends. But reordering will make report analysis25// 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.28static 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 vars34// with e.g. alignment 1 and alignment 16 do not get reordered by CompareVars.35static 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.40static 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 52ASanStackFrameLayout53ComputeASanStackFrameLayout(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 96SmallString<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 114SmallVector<uint8_t, 64>115GetShadowBytes(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 133SmallVector<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 namespace152