1//===- OutputSegment.cpp --------------------------------------------------===//
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 "OutputSegment.h"
10#include "ConcatOutputSection.h"
11#include "InputSection.h"
12#include "Symbols.h"
13#include "SyntheticSections.h"
14
15#include "lld/Common/ErrorHandler.h"
16#include "lld/Common/Memory.h"
17#include "llvm/ADT/StringSwitch.h"
18#include "llvm/BinaryFormat/MachO.h"
19
20using namespace llvm;
21using namespace llvm::MachO;
22using namespace lld;
23using namespace lld::macho;
24
25static uint32_t initProt(StringRef name) {
26 auto it = find_if(
27 Range&: config->segmentProtections,
28 P: [&](const SegmentProtection &segprot) { return segprot.name == name; });
29 if (it != config->segmentProtections.end())
30 return it->initProt;
31
32 if (name == segment_names::text)
33 return VM_PROT_READ | VM_PROT_EXECUTE;
34 if (name == segment_names::pageZero)
35 return 0;
36 if (name == segment_names::linkEdit)
37 return VM_PROT_READ;
38 return VM_PROT_READ | VM_PROT_WRITE;
39}
40
41static uint32_t maxProt(StringRef name) {
42 assert(config->arch() != AK_i386 &&
43 "TODO: i386 has different maxProt requirements");
44 return initProt(name);
45}
46
47static uint32_t flags(StringRef name) {
48 // If we ever implement shared cache output support, SG_READ_ONLY should not
49 // be used for dylibs that can be placed in it.
50 return name == segment_names::dataConst ? (uint32_t)SG_READ_ONLY : 0;
51}
52
53size_t OutputSegment::numNonHiddenSections() const {
54 size_t count = 0;
55 for (const OutputSection *osec : sections)
56 count += (!osec->isHidden() ? 1 : 0);
57 return count;
58}
59
60void OutputSegment::addOutputSection(OutputSection *osec) {
61 inputOrder = std::min(a: inputOrder, b: osec->inputOrder);
62
63 osec->parent = this;
64 sections.push_back(x: osec);
65
66 for (const SectionAlign &sectAlign : config->sectionAlignments)
67 if (sectAlign.segName == name && sectAlign.sectName == osec->name)
68 osec->align = sectAlign.align;
69}
70
71template <typename T, typename F> static auto compareByOrder(F ord) {
72 return [=](T a, T b) { return ord(a) < ord(b); };
73}
74
75static int segmentOrder(OutputSegment *seg) {
76 return StringSwitch<int>(seg->name)
77 .Case(S: segment_names::pageZero, Value: -4)
78 .Case(S: segment_names::text, Value: -3)
79 .Case(S: segment_names::dataConst, Value: -2)
80 .Case(S: segment_names::data, Value: -1)
81 .Case(S: segment_names::llvm, Value: std::numeric_limits<int>::max() - 1)
82 // Make sure __LINKEDIT is the last segment (i.e. all its hidden
83 // sections must be ordered after other sections).
84 .Case(S: segment_names::linkEdit, Value: std::numeric_limits<int>::max())
85 .Default(Value: seg->inputOrder);
86}
87
88static int sectionOrder(OutputSection *osec) {
89 StringRef segname = osec->parent->name;
90 // Sections are uniquely identified by their segment + section name.
91 if (segname == segment_names::text) {
92 return StringSwitch<int>(osec->name)
93 .Case(S: section_names::header, Value: -6)
94 .Case(S: section_names::text, Value: -5)
95 .Case(S: section_names::stubs, Value: -4)
96 .Case(S: section_names::stubHelper, Value: -3)
97 .Case(S: section_names::objcStubs, Value: -2)
98 .Case(S: section_names::initOffsets, Value: -1)
99 .Case(S: section_names::unwindInfo, Value: std::numeric_limits<int>::max() - 1)
100 .Case(S: section_names::ehFrame, Value: std::numeric_limits<int>::max())
101 .Default(Value: osec->inputOrder);
102 } else if (segname == segment_names::data ||
103 segname == segment_names::dataConst) {
104 // For each thread spawned, dyld will initialize its TLVs by copying the
105 // address range from the start of the first thread-local data section to
106 // the end of the last one. We therefore arrange these sections contiguously
107 // to minimize the amount of memory used. Additionally, since zerofill
108 // sections must be at the end of their segments, and since TLV data
109 // sections can be zerofills, we end up putting all TLV data sections at the
110 // end of the segment.
111 switch (sectionType(flags: osec->flags)) {
112 case S_THREAD_LOCAL_VARIABLE_POINTERS:
113 return std::numeric_limits<int>::max() - 3;
114 case S_THREAD_LOCAL_REGULAR:
115 return std::numeric_limits<int>::max() - 2;
116 case S_THREAD_LOCAL_ZEROFILL:
117 return std::numeric_limits<int>::max() - 1;
118 case S_ZEROFILL:
119 return std::numeric_limits<int>::max();
120 default:
121 return StringSwitch<int>(osec->name)
122 .Case(S: section_names::got, Value: -3)
123 .Case(S: section_names::lazySymbolPtr, Value: -2)
124 .Case(S: section_names::const_, Value: -1)
125 .Default(Value: osec->inputOrder);
126 }
127 } else if (segname == segment_names::linkEdit) {
128 return StringSwitch<int>(osec->name)
129 .Case(S: section_names::chainFixups, Value: -11)
130 .Case(S: section_names::rebase, Value: -10)
131 .Case(S: section_names::binding, Value: -9)
132 .Case(S: section_names::weakBinding, Value: -8)
133 .Case(S: section_names::lazyBinding, Value: -7)
134 .Case(S: section_names::export_, Value: -6)
135 .Case(S: section_names::functionStarts, Value: -5)
136 .Case(S: section_names::dataInCode, Value: -4)
137 .Case(S: section_names::symbolTable, Value: -3)
138 .Case(S: section_names::indirectSymbolTable, Value: -2)
139 .Case(S: section_names::stringTable, Value: -1)
140 .Case(S: section_names::codeSignature, Value: std::numeric_limits<int>::max())
141 .Default(Value: osec->inputOrder);
142 }
143 // ZeroFill sections must always be the at the end of their segments:
144 // dyld checks if a segment's file size is smaller than its in-memory
145 // size to detect if a segment has zerofill sections, and if so it maps
146 // the missing tail as zerofill.
147 if (sectionType(flags: osec->flags) == S_ZEROFILL)
148 return std::numeric_limits<int>::max();
149 return osec->inputOrder;
150}
151
152void OutputSegment::sortOutputSections() {
153 // Must be stable_sort() to keep special sections such as
154 // S_THREAD_LOCAL_REGULAR in input order.
155 llvm::stable_sort(Range&: sections, C: compareByOrder<OutputSection *>(ord: sectionOrder));
156}
157
158void OutputSegment::assignAddressesToStartEndSymbols() {
159 for (Defined *d : segmentStartSymbols)
160 d->value = addr;
161 for (Defined *d : segmentEndSymbols)
162 d->value = addr + vmSize;
163}
164
165void macho::sortOutputSegments() {
166 llvm::stable_sort(Range&: outputSegments,
167 C: compareByOrder<OutputSegment *>(ord: segmentOrder));
168}
169
170static DenseMap<StringRef, OutputSegment *> nameToOutputSegment;
171std::vector<OutputSegment *> macho::outputSegments;
172
173void macho::resetOutputSegments() {
174 outputSegments.clear();
175 nameToOutputSegment.clear();
176}
177
178static StringRef maybeRenameSegment(StringRef name) {
179 auto newName = config->segmentRenameMap.find(Val: name);
180 if (newName != config->segmentRenameMap.end())
181 return newName->second;
182 return name;
183}
184
185OutputSegment *macho::getOrCreateOutputSegment(StringRef name) {
186 name = maybeRenameSegment(name);
187
188 OutputSegment *&segRef = nameToOutputSegment[name];
189 if (segRef)
190 return segRef;
191
192 segRef = make<OutputSegment>();
193 segRef->name = name;
194 segRef->maxProt = maxProt(name);
195 segRef->initProt = initProt(name);
196 segRef->flags = flags(name);
197
198 outputSegments.push_back(x: segRef);
199 return segRef;
200}
201

source code of lld/MachO/OutputSegment.cpp