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 "llvm/Support/MathExtras.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.
CompareVars(const ASanStackVariableDescription & a,const ASanStackVariableDescription & b)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 size_t kMinAlignment = 16;
36
37 // The larger the variable Size the larger is the redzone.
38 // The resulting frame size is a multiple of Alignment.
VarAndRedzoneSize(size_t Size,size_t Alignment)39 static size_t VarAndRedzoneSize(size_t Size, size_t Alignment) {
40 size_t Res = 0;
41 if (Size <= 4) Res = 16;
42 else if (Size <= 16) Res = 32;
43 else if (Size <= 128) Res = Size + 32;
44 else if (Size <= 512) Res = Size + 64;
45 else if (Size <= 4096) Res = Size + 128;
46 else Res = Size + 256;
47 return RoundUpToAlignment(Res, Alignment);
48 }
49
50 void
ComputeASanStackFrameLayout(SmallVectorImpl<ASanStackVariableDescription> & Vars,size_t Granularity,size_t MinHeaderSize,ASanStackFrameLayout * Layout)51 ComputeASanStackFrameLayout(SmallVectorImpl<ASanStackVariableDescription> &Vars,
52 size_t Granularity, size_t MinHeaderSize,
53 ASanStackFrameLayout *Layout) {
54 assert(Granularity >= 8 && Granularity <= 64 &&
55 (Granularity & (Granularity - 1)) == 0);
56 assert(MinHeaderSize >= 16 && (MinHeaderSize & (MinHeaderSize - 1)) == 0 &&
57 MinHeaderSize >= Granularity);
58 size_t NumVars = Vars.size();
59 assert(NumVars > 0);
60 for (size_t i = 0; i < NumVars; i++)
61 Vars[i].Alignment = std::max(Vars[i].Alignment, kMinAlignment);
62
63 std::stable_sort(Vars.begin(), Vars.end(), CompareVars);
64 SmallString<2048> StackDescriptionStorage;
65 raw_svector_ostream StackDescription(StackDescriptionStorage);
66 StackDescription << NumVars;
67 Layout->FrameAlignment = std::max(Granularity, Vars[0].Alignment);
68 SmallVector<uint8_t, 64> &SB(Layout->ShadowBytes);
69 SB.clear();
70 size_t Offset = std::max(std::max(MinHeaderSize, Granularity),
71 Vars[0].Alignment);
72 assert((Offset % Granularity) == 0);
73 SB.insert(SB.end(), Offset / Granularity, kAsanStackLeftRedzoneMagic);
74 for (size_t i = 0; i < NumVars; i++) {
75 bool IsLast = i == NumVars - 1;
76 size_t Alignment = std::max(Granularity, Vars[i].Alignment);
77 (void)Alignment; // Used only in asserts.
78 size_t Size = Vars[i].Size;
79 const char *Name = Vars[i].Name;
80 assert((Alignment & (Alignment - 1)) == 0);
81 assert(Layout->FrameAlignment >= Alignment);
82 assert((Offset % Alignment) == 0);
83 assert(Size > 0);
84 StackDescription << " " << Offset << " " << Size << " " << strlen(Name)
85 << " " << Name;
86 size_t NextAlignment = IsLast ? Granularity
87 : std::max(Granularity, Vars[i + 1].Alignment);
88 size_t SizeWithRedzone = VarAndRedzoneSize(Vars[i].Size, NextAlignment);
89 SB.insert(SB.end(), Size / Granularity, 0);
90 if (Size % Granularity)
91 SB.insert(SB.end(), Size % Granularity);
92 SB.insert(SB.end(), (SizeWithRedzone - Size) / Granularity,
93 IsLast ? kAsanStackRightRedzoneMagic
94 : kAsanStackMidRedzoneMagic);
95 Vars[i].Offset = Offset;
96 Offset += SizeWithRedzone;
97 }
98 if (Offset % MinHeaderSize) {
99 size_t ExtraRedzone = MinHeaderSize - (Offset % MinHeaderSize);
100 SB.insert(SB.end(), ExtraRedzone / Granularity,
101 kAsanStackRightRedzoneMagic);
102 Offset += ExtraRedzone;
103 }
104 Layout->DescriptionString = StackDescription.str();
105 Layout->FrameSize = Offset;
106 assert((Layout->FrameSize % MinHeaderSize) == 0);
107 assert(Layout->FrameSize / Granularity == Layout->ShadowBytes.size());
108 }
109
110 } // llvm namespace
111