LLVM 17.0.0git
SafeStackLayout.cpp
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1//===- SafeStackLayout.cpp - SafeStack frame layout -----------------------===//
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#include "SafeStackLayout.h"
10#include "llvm/IR/Value.h"
13#include "llvm/Support/Debug.h"
15#include <algorithm>
16#include <cassert>
17
18using namespace llvm;
19using namespace llvm::safestack;
20
21#define DEBUG_TYPE "safestacklayout"
22
23static cl::opt<bool> ClLayout("safe-stack-layout",
24 cl::desc("enable safe stack layout"), cl::Hidden,
25 cl::init(true));
26
28 OS << "Stack regions:\n";
29 for (unsigned i = 0; i < Regions.size(); ++i) {
30 OS << " " << i << ": [" << Regions[i].Start << ", " << Regions[i].End
31 << "), range " << Regions[i].Range << "\n";
32 }
33 OS << "Stack objects:\n";
34 for (auto &IT : ObjectOffsets) {
35 OS << " at " << IT.getSecond() << ": " << *IT.getFirst() << "\n";
36 }
37}
38
39void StackLayout::addObject(const Value *V, unsigned Size, Align Alignment,
40 const StackLifetime::LiveRange &Range) {
41 StackObjects.push_back({V, Size, Alignment, Range});
42 ObjectAlignments[V] = Alignment;
43 MaxAlignment = std::max(MaxAlignment, Alignment);
44}
45
46static unsigned AdjustStackOffset(unsigned Offset, unsigned Size,
47 Align Alignment) {
48 return alignTo(Offset + Size, Alignment) - Size;
49}
50
51void StackLayout::layoutObject(StackObject &Obj) {
52 if (!ClLayout) {
53 // If layout is disabled, just grab the next aligned address.
54 // This effectively disables stack coloring as well.
55 unsigned LastRegionEnd = Regions.empty() ? 0 : Regions.back().End;
56 unsigned Start = AdjustStackOffset(LastRegionEnd, Obj.Size, Obj.Alignment);
57 unsigned End = Start + Obj.Size;
58 Regions.emplace_back(Start, End, Obj.Range);
59 ObjectOffsets[Obj.Handle] = End;
60 return;
61 }
62
63 LLVM_DEBUG(dbgs() << "Layout: size " << Obj.Size << ", align "
64 << Obj.Alignment.value() << ", range " << Obj.Range
65 << "\n");
66 assert(Obj.Alignment <= MaxAlignment);
67 unsigned Start = AdjustStackOffset(0, Obj.Size, Obj.Alignment);
68 unsigned End = Start + Obj.Size;
69 LLVM_DEBUG(dbgs() << " First candidate: " << Start << " .. " << End << "\n");
70 for (const StackRegion &R : Regions) {
71 LLVM_DEBUG(dbgs() << " Examining region: " << R.Start << " .. " << R.End
72 << ", range " << R.Range << "\n");
73 assert(End >= R.Start);
74 if (Start >= R.End) {
75 LLVM_DEBUG(dbgs() << " Does not intersect, skip.\n");
76 continue;
77 }
78 if (Obj.Range.overlaps(R.Range)) {
79 // Find the next appropriate location.
80 Start = AdjustStackOffset(R.End, Obj.Size, Obj.Alignment);
81 End = Start + Obj.Size;
82 LLVM_DEBUG(dbgs() << " Overlaps. Next candidate: " << Start << " .. "
83 << End << "\n");
84 continue;
85 }
86 if (End <= R.End) {
87 LLVM_DEBUG(dbgs() << " Reusing region(s).\n");
88 break;
89 }
90 }
91
92 unsigned LastRegionEnd = Regions.empty() ? 0 : Regions.back().End;
93 if (End > LastRegionEnd) {
94 // Insert a new region at the end. Maybe two.
95 if (Start > LastRegionEnd) {
96 LLVM_DEBUG(dbgs() << " Creating gap region: " << LastRegionEnd << " .. "
97 << Start << "\n");
98 Regions.emplace_back(LastRegionEnd, Start, StackLifetime::LiveRange(0));
99 LastRegionEnd = Start;
100 }
101 LLVM_DEBUG(dbgs() << " Creating new region: " << LastRegionEnd << " .. "
102 << End << ", range " << Obj.Range << "\n");
103 Regions.emplace_back(LastRegionEnd, End, Obj.Range);
104 LastRegionEnd = End;
105 }
106
107 // Split starting and ending regions if necessary.
108 for (unsigned i = 0; i < Regions.size(); ++i) {
109 StackRegion &R = Regions[i];
110 if (Start > R.Start && Start < R.End) {
111 StackRegion R0 = R;
112 R.Start = R0.End = Start;
113 Regions.insert(&R, R0);
114 continue;
115 }
116 if (End > R.Start && End < R.End) {
117 StackRegion R0 = R;
118 R0.End = R.Start = End;
119 Regions.insert(&R, R0);
120 break;
121 }
122 }
123
124 // Update live ranges for all affected regions.
125 for (StackRegion &R : Regions) {
126 if (Start < R.End && End > R.Start)
127 R.Range.join(Obj.Range);
128 if (End <= R.End)
129 break;
130 }
131
132 ObjectOffsets[Obj.Handle] = End;
133}
134
136 // Simple greedy algorithm.
137 // If this is replaced with something smarter, it must preserve the property
138 // that the first object is always at the offset 0 in the stack frame (for
139 // StackProtectorSlot), or handle stack protector in some other way.
140
141 // Sort objects by size (largest first) to reduce fragmentation.
142 if (StackObjects.size() > 2)
143 llvm::stable_sort(drop_begin(StackObjects),
144 [](const StackObject &a, const StackObject &b) {
145 return a.Size > b.Size;
146 });
147
148 for (auto &Obj : StackObjects)
149 layoutObject(Obj);
150
152}
static cl::opt< ITMode > IT(cl::desc("IT block support"), cl::Hidden, cl::init(DefaultIT), cl::values(clEnumValN(DefaultIT, "arm-default-it", "Generate any type of IT block"), clEnumValN(RestrictedIT, "arm-restrict-it", "Disallow complex IT blocks")))
#define LLVM_DUMP_METHOD
Mark debug helper function definitions like dump() that should not be stripped from debug builds.
Definition: Compiler.h:492
#define LLVM_DEBUG(X)
Definition: Debug.h:101
uint64_t Size
static void AdjustStackOffset(MachineFrameInfo &MFI, int FrameIdx, bool StackGrowsDown, int64_t &Offset, Align &MaxAlign, unsigned Skew)
AdjustStackOffset - Helper function used to adjust the stack frame offset.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
static cl::opt< bool > ClLayout("safe-stack-layout", cl::desc("enable safe stack layout"), cl::Hidden, cl::init(true))
bool empty() const
Definition: SmallVector.h:94
size_t size() const
Definition: SmallVector.h:91
reference emplace_back(ArgTypes &&... Args)
Definition: SmallVector.h:941
void push_back(const T &Elt)
Definition: SmallVector.h:416
This class represents a set of interesting instructions where an alloca is live.
Definition: StackLifetime.h:63
LLVM Value Representation.
Definition: Value.h:74
This class implements an extremely fast bulk output stream that can only output to a stream.
Definition: raw_ostream.h:52
void computeLayout()
Run the layout computation for all previously added objects.
void print(raw_ostream &OS)
void addObject(const Value *V, unsigned Size, Align Alignment, const StackLifetime::LiveRange &Range)
Add an object to the stack frame.
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:445
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
auto drop_begin(T &&RangeOrContainer, size_t N=1)
Return a range covering RangeOrContainer with the first N elements excluded.
Definition: STLExtras.h:386
@ Offset
Definition: DWP.cpp:406
void stable_sort(R &&Range)
Definition: STLExtras.h:1948
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
uint64_t alignTo(uint64_t Size, Align A)
Returns a multiple of A needed to store Size bytes.
Definition: Alignment.h:155
This struct is a compact representation of a valid (non-zero power of two) alignment.
Definition: Alignment.h:39