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
19namespace 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.
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 vars
34// 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(Value: std::max(a: Res, b: 2 * Granularity), Align: Alignment);
50}
51
52ASanStackFrameLayout
53ComputeASanStackFrameLayout(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(a: Vars[i].Alignment, b: kMinAlignment);
63
64 llvm::stable_sort(Range&: Vars, C: CompareVars);
65
66 ASanStackFrameLayout Layout;
67 Layout.Granularity = Granularity;
68 Layout.FrameAlignment = std::max(a: Granularity, b: Vars[0].Alignment);
69 uint64_t Offset =
70 std::max(a: std::max(a: MinHeaderSize, b: Granularity), b: 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(a: Granularity, b: 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(a: Granularity, b: Vars[i + 1].Alignment);
83 uint64_t SizeWithRedzone =
84 VarAndRedzoneSize(Size, Granularity, Alignment: 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(Value: 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(N: Vars[0].Offset / Granularity, NV: kAsanStackLeftRedzoneMagic);
122 for (const auto &Var : Vars) {
123 SB.resize(N: Var.Offset / Granularity, NV: kAsanStackMidRedzoneMagic);
124
125 SB.resize(N: SB.size() + Var.Size / Granularity, NV: 0);
126 if (Var.Size % Granularity)
127 SB.push_back(Elt: Var.Size % Granularity);
128 }
129 SB.resize(N: Layout.FrameSize / Granularity, NV: 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(first: SB.begin() + Offset, last: SB.begin() + Offset + LifetimeShadowSize,
145 value: kAsanStackUseAfterScopeMagic);
146 }
147
148 return SB;
149}
150
151} // llvm namespace
152