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1 //===- OutputSections.h -----------------------------------------*- C++ -*-===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8
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9 #ifndef LLD_ELF_OUTPUT_SECTIONS_H
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10 #define LLD_ELF_OUTPUT_SECTIONS_H
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11
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12 #include "Config.h"
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13 #include "InputSection.h"
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14 #include "LinkerScript.h"
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15 #include "Relocations.h"
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16 #include "lld/Common/LLVM.h"
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17 #include "llvm/MC/StringTableBuilder.h"
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18 #include "llvm/Object/ELF.h"
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19 #include <array>
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20
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21 namespace lld {
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22 namespace elf {
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23
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24 struct PhdrEntry;
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25 class InputSection;
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26 class InputSectionBase;
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27
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28 // This represents a section in an output file.
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29 // It is composed of multiple InputSections.
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30 // The writer creates multiple OutputSections and assign them unique,
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31 // non-overlapping file offsets and VAs.
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32 class OutputSection final : public BaseCommand, public SectionBase {
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33 public:
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34 OutputSection(StringRef name, uint32_t type, uint64_t flags);
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35
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36 static bool classof(const SectionBase *s) {
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37 return s->kind() == SectionBase::Output;
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38 }
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39
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40 static bool classof(const BaseCommand *c);
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41
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42 uint64_t getLMA() const { return ptLoad ? addr + ptLoad->lmaOffset : addr; }
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43 template <typename ELFT> void writeHeaderTo(typename ELFT::Shdr *sHdr);
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44
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45 uint32_t sectionIndex = UINT32_MAX;
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46 unsigned sortRank;
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47
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48 uint32_t getPhdrFlags() const;
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49
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50 // Pointer to the PT_LOAD segment, which this section resides in. This field
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51 // is used to correctly compute file offset of a section. When two sections
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52 // share the same load segment, difference between their file offsets should
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53 // be equal to difference between their virtual addresses. To compute some
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54 // section offset we use the following formula: Off = Off_first + VA -
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55 // VA_first, where Off_first and VA_first is file offset and VA of first
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56 // section in PT_LOAD.
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57 PhdrEntry *ptLoad = nullptr;
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58
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59 // Pointer to a relocation section for this section. Usually nullptr because
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60 // we consume relocations, but if --emit-relocs is specified (which is rare),
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61 // it may have a non-null value.
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62 OutputSection *relocationSection = nullptr;
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63
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64 // Initially this field is the number of InputSections that have been added to
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65 // the OutputSection so far. Later on, after a call to assignAddresses, it
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66 // corresponds to the Elf_Shdr member.
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67 uint64_t size = 0;
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68
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69 // The following fields correspond to Elf_Shdr members.
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70 uint64_t offset = 0;
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71 uint64_t addr = 0;
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72 uint32_t shName = 0;
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73
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74 void recordSection(InputSectionBase *isec);
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75 void commitSection(InputSection *isec);
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76 void finalizeInputSections();
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77
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78 // The following members are normally only used in linker scripts.
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79 MemoryRegion *memRegion = nullptr;
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80 MemoryRegion *lmaRegion = nullptr;
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81 Expr addrExpr;
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82 Expr alignExpr;
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83 Expr lmaExpr;
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84 Expr subalignExpr;
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85 std::vector<BaseCommand *> sectionCommands;
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86 std::vector<StringRef> phdrs;
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87 llvm::Optional<std::array<uint8_t, 4>> filler;
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88 ConstraintKind constraint = ConstraintKind::NoConstraint;
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89 std::string location;
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90 std::string memoryRegionName;
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91 std::string lmaRegionName;
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92 bool nonAlloc = false;
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93 bool noload = false;
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94 bool expressionsUseSymbols = false;
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95 bool usedInExpression = false;
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96 bool inOverlay = false;
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97
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98 // Tracks whether the section has ever had an input section added to it, even
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99 // if the section was later removed (e.g. because it is a synthetic section
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100 // that wasn't needed). This is needed for orphan placement.
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101 bool hasInputSections = false;
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102
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103 void finalize();
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104 template <class ELFT> void writeTo(uint8_t *buf);
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105 template <class ELFT> void maybeCompress();
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106
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107 void sort(llvm::function_ref<int(InputSectionBase *s)> order);
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108 void sortInitFini();
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109 void sortCtorsDtors();
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110
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111 private:
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112 // Used for implementation of --compress-debug-sections option.
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113 std::vector<uint8_t> zDebugHeader;
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114 llvm::SmallVector<char, 1> compressedData;
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115
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116 std::array<uint8_t, 4> getFiller();
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117 };
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118
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119 int getPriority(StringRef s);
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120
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121 InputSection *getFirstInputSection(const OutputSection *os);
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122 std::vector<InputSection *> getInputSections(const OutputSection *os);
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123
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124 // All output sections that are handled by the linker specially are
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125 // globally accessible. Writer initializes them, so don't use them
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126 // until Writer is initialized.
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127 struct Out {
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128 static uint8_t *bufferStart;
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129 static uint8_t first;
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130 static PhdrEntry *tlsPhdr;
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131 static OutputSection *elfHeader;
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132 static OutputSection *programHeaders;
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133 static OutputSection *preinitArray;
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134 static OutputSection *initArray;
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135 static OutputSection *finiArray;
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136 };
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137
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138 } // namespace elf
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139 } // namespace lld
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140
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141 namespace lld {
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142 namespace elf {
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143
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144 uint64_t getHeaderSize();
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145
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146 extern std::vector<OutputSection *> outputSections;
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147 } // namespace elf
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148 } // namespace lld
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149
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150 #endif
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