1//===- OutputSections.h -----------------------------------------*- C++ -*-===//
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#ifndef LLD_ELF_OUTPUT_SECTIONS_H
10#define LLD_ELF_OUTPUT_SECTIONS_H
11
12#include "InputSection.h"
13#include "LinkerScript.h"
14#include "lld/Common/LLVM.h"
15#include "llvm/Support/Compiler.h"
16#include "llvm/Support/Parallel.h"
17
18#include <array>
19
20namespace lld::elf {
21
22struct PhdrEntry;
23
24struct CompressedData {
25  std::unique_ptr<SmallVector<uint8_t, 0>[]> shards;
26  uint32_t numShards = 0;
27  uint32_t checksum = 0;
28  uint64_t uncompressedSize;
29};
30
31// This represents a section in an output file.
32// It is composed of multiple InputSections.
33// The writer creates multiple OutputSections and assign them unique,
34// non-overlapping file offsets and VAs.
35class OutputSection final : public SectionBase {
36public:
37  OutputSection(StringRef name, uint32_t type, uint64_t flags);
38
39  static bool classof(const SectionBase *s) {
40    return s->kind() == SectionBase::Output;
41  }
42
43  uint64_t getLMA() const { return ptLoad ? addr + ptLoad->lmaOffset : addr; }
44  template <typename ELFT> void writeHeaderTo(typename ELFT::Shdr *sHdr);
45
46  uint32_t sectionIndex = UINT32_MAX;
47  unsigned sortRank;
48
49  uint32_t getPhdrFlags() const;
50
51  // Pointer to the PT_LOAD segment, which this section resides in. This field
52  // is used to correctly compute file offset of a section. When two sections
53  // share the same load segment, difference between their file offsets should
54  // be equal to difference between their virtual addresses. To compute some
55  // section offset we use the following formula: Off = Off_first + VA -
56  // VA_first, where Off_first and VA_first is file offset and VA of first
57  // section in PT_LOAD.
58  PhdrEntry *ptLoad = nullptr;
59
60  // Pointer to a relocation section for this section. Usually nullptr because
61  // we consume relocations, but if --emit-relocs is specified (which is rare),
62  // it may have a non-null value.
63  OutputSection *relocationSection = nullptr;
64
65  // Initially this field is the number of InputSections that have been added to
66  // the OutputSection so far. Later on, after a call to assignAddresses, it
67  // corresponds to the Elf_Shdr member.
68  uint64_t size = 0;
69
70  // The following fields correspond to Elf_Shdr members.
71  uint64_t offset = 0;
72  uint64_t addr = 0;
73  uint32_t shName = 0;
74
75  void recordSection(InputSectionBase *isec);
76  void commitSection(InputSection *isec);
77  void finalizeInputSections();
78
79  // The following members are normally only used in linker scripts.
80  MemoryRegion *memRegion = nullptr;
81  MemoryRegion *lmaRegion = nullptr;
82  Expr addrExpr;
83  Expr alignExpr;
84  Expr lmaExpr;
85  Expr subalignExpr;
86  SmallVector<SectionCommand *, 0> commands;
87  SmallVector<StringRef, 0> phdrs;
88  std::optional<std::array<uint8_t, 4>> filler;
89  ConstraintKind constraint = ConstraintKind::NoConstraint;
90  std::string location;
91  std::string memoryRegionName;
92  std::string lmaRegionName;
93  bool nonAlloc = false;
94  bool typeIsSet = false;
95  bool expressionsUseSymbols = false;
96  bool usedInExpression = false;
97  bool inOverlay = false;
98
99  // Tracks whether the section has ever had an input section added to it, even
100  // if the section was later removed (e.g. because it is a synthetic section
101  // that wasn't needed). This is needed for orphan placement.
102  bool hasInputSections = false;
103
104  // The output section description is specified between DATA_SEGMENT_ALIGN and
105  // DATA_RELRO_END.
106  bool relro = false;
107
108  void finalize();
109  template <class ELFT>
110  void writeTo(uint8_t *buf, llvm::parallel::TaskGroup &tg);
111  // Check that the addends for dynamic relocations were written correctly.
112  void checkDynRelAddends(const uint8_t *bufStart);
113  template <class ELFT> void maybeCompress();
114
115  void sort(llvm::function_ref<int(InputSectionBase *s)> order);
116  void sortInitFini();
117  void sortCtorsDtors();
118
119private:
120  SmallVector<InputSection *, 0> storage;
121
122  // Used for implementation of --compress-debug-sections option.
123  CompressedData compressed;
124
125  std::array<uint8_t, 4> getFiller();
126};
127
128struct OutputDesc final : SectionCommand {
129  OutputSection osec;
130  OutputDesc(StringRef name, uint32_t type, uint64_t flags)
131      : SectionCommand(OutputSectionKind), osec(name, type, flags) {}
132
133  static bool classof(const SectionCommand *c) {
134    return c->kind == OutputSectionKind;
135  }
136};
137
138int getPriority(StringRef s);
139
140InputSection *getFirstInputSection(const OutputSection *os);
141llvm::ArrayRef<InputSection *>
142getInputSections(const OutputSection &os,
143                 SmallVector<InputSection *, 0> &storage);
144
145// All output sections that are handled by the linker specially are
146// globally accessible. Writer initializes them, so don't use them
147// until Writer is initialized.
148struct Out {
149  static uint8_t *bufferStart;
150  static PhdrEntry *tlsPhdr;
151  static OutputSection *elfHeader;
152  static OutputSection *programHeaders;
153  static OutputSection *preinitArray;
154  static OutputSection *initArray;
155  static OutputSection *finiArray;
156};
157
158uint64_t getHeaderSize();
159
160LLVM_LIBRARY_VISIBILITY extern llvm::SmallVector<OutputSection *, 0>
161    outputSections;
162} // namespace lld::elf
163
164#endif
165