OutputSections.h revision 360784 
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 "Config.h"
13#include "InputSection.h"
14#include "LinkerScript.h"
15#include "Relocations.h"
16#include "lld/Common/LLVM.h"
17#include "llvm/MC/StringTableBuilder.h"
18#include "llvm/Object/ELF.h"
19#include <array>
20
21namespace lld {
22namespace elf {
23
24struct PhdrEntry;
25class InputSection;
26class InputSectionBase;
27
28// This represents a section in an output file.
29// It is composed of multiple InputSections.
30// The writer creates multiple OutputSections and assign them unique,
31// non-overlapping file offsets and VAs.
32class OutputSection final : public BaseCommand, public SectionBase {
33public:
34  OutputSection(StringRef name, uint32_t type, uint64_t flags);
35
36  static bool classof(const SectionBase *s) {
37    return s->kind() == SectionBase::Output;
38  }
39
40  static bool classof(const BaseCommand *c);
41
42  uint64_t getLMA() const { return ptLoad ? addr + ptLoad->lmaOffset : addr; }
43  template <typename ELFT> void writeHeaderTo(typename ELFT::Shdr *sHdr);
44
45  uint32_t sectionIndex = UINT32_MAX;
46  unsigned sortRank;
47
48  uint32_t getPhdrFlags() const;
49
50  // Pointer to the PT_LOAD segment, which this section resides in. This field
51  // is used to correctly compute file offset of a section. When two sections
52  // share the same load segment, difference between their file offsets should
53  // be equal to difference between their virtual addresses. To compute some
54  // section offset we use the following formula: Off = Off_first + VA -
55  // VA_first, where Off_first and VA_first is file offset and VA of first
56  // section in PT_LOAD.
57  PhdrEntry *ptLoad = nullptr;
58
59  // Pointer to a relocation section for this section. Usually nullptr because
60  // we consume relocations, but if --emit-relocs is specified (which is rare),
61  // it may have a non-null value.
62  OutputSection *relocationSection = nullptr;
63
64  // Initially this field is the number of InputSections that have been added to
65  // the OutputSection so far. Later on, after a call to assignAddresses, it
66  // corresponds to the Elf_Shdr member.
67  uint64_t size = 0;
68
69  // The following fields correspond to Elf_Shdr members.
70  uint64_t offset = 0;
71  uint64_t addr = 0;
72  uint32_t shName = 0;
73
74  void recordSection(InputSectionBase *isec);
75  void commitSection(InputSection *isec);
76  void finalizeInputSections();
77
78  // The following members are normally only used in linker scripts.
79  MemoryRegion *memRegion = nullptr;
80  MemoryRegion *lmaRegion = nullptr;
81  Expr addrExpr;
82  Expr alignExpr;
83  Expr lmaExpr;
84  Expr subalignExpr;
85  std::vector<BaseCommand *> sectionCommands;
86  std::vector<StringRef> phdrs;
87  llvm::Optional<std::array<uint8_t, 4>> filler;
88  ConstraintKind constraint = ConstraintKind::NoConstraint;
89  std::string location;
90  std::string memoryRegionName;
91  std::string lmaRegionName;
92  bool nonAlloc = false;
93  bool noload = false;
94  bool expressionsUseSymbols = false;
95  bool usedInExpression = false;
96  bool inOverlay = false;
97
98  // Tracks whether the section has ever had an input section added to it, even
99  // if the section was later removed (e.g. because it is a synthetic section
100  // that wasn't needed). This is needed for orphan placement.
101  bool hasInputSections = false;
102
103  void finalize();
104  template <class ELFT> void writeTo(uint8_t *buf);
105  template <class ELFT> void maybeCompress();
106
107  void sort(llvm::function_ref<int(InputSectionBase *s)> order);
108  void sortInitFini();
109  void sortCtorsDtors();
110
111private:
112  // Used for implementation of --compress-debug-sections option.
113  std::vector<uint8_t> zDebugHeader;
114  llvm::SmallVector<char, 1> compressedData;
115
116  std::array<uint8_t, 4> getFiller();
117};
118
119int getPriority(StringRef s);
120
121std::vector<InputSection *> getInputSections(OutputSection* os);
122
123// All output sections that are handled by the linker specially are
124// globally accessible. Writer initializes them, so don't use them
125// until Writer is initialized.
126struct Out {
127  static uint8_t *bufferStart;
128  static uint8_t first;
129  static PhdrEntry *tlsPhdr;
130  static OutputSection *elfHeader;
131  static OutputSection *programHeaders;
132  static OutputSection *preinitArray;
133  static OutputSection *initArray;
134  static OutputSection *finiArray;
135};
136
137} // namespace elf
138} // namespace lld
139
140namespace lld {
141namespace elf {
142
143uint64_t getHeaderSize();
144
145extern std::vector<OutputSection *> outputSections;
146} // namespace elf
147} // namespace lld
148
149#endif
150