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 type = 0;
27 uint32_t numShards = 0;
28 uint32_t checksum = 0;
29 uint64_t uncompressedSize;
30};
31
32// This represents a section in an output file.
33// It is composed of multiple InputSections.
34// The writer creates multiple OutputSections and assign them unique,
35// non-overlapping file offsets and VAs.
36class OutputSection final : public SectionBase {
37public:
38 OutputSection(StringRef name, uint32_t type, uint64_t flags);
39
40 static bool classof(const SectionBase *s) {
41 return s->kind() == SectionBase::Output;
42 }
43
44 uint64_t getLMA() const { return ptLoad ? addr + ptLoad->lmaOffset : addr; }
45 template <typename ELFT> void writeHeaderTo(typename ELFT::Shdr *sHdr);
46
47 uint32_t sectionIndex = UINT32_MAX;
48 unsigned sortRank;
49
50 uint32_t getPhdrFlags() const;
51
52 // Pointer to the PT_LOAD segment, which this section resides in. This field
53 // is used to correctly compute file offset of a section. When two sections
54 // share the same load segment, difference between their file offsets should
55 // be equal to difference between their virtual addresses. To compute some
56 // section offset we use the following formula: Off = Off_first + VA -
57 // VA_first, where Off_first and VA_first is file offset and VA of first
58 // section in PT_LOAD.
59 PhdrEntry *ptLoad = nullptr;
60
61 // Pointer to a relocation section for this section. Usually nullptr because
62 // we consume relocations, but if --emit-relocs is specified (which is rare),
63 // it may have a non-null value.
64 OutputSection *relocationSection = nullptr;
65
66 // Initially this field is the number of InputSections that have been added to
67 // the OutputSection so far. Later on, after a call to assignAddresses, it
68 // corresponds to the Elf_Shdr member.
69 uint64_t size = 0;
70
71 // The following fields correspond to Elf_Shdr members.
72 uint64_t offset = 0;
73 uint64_t addr = 0;
74 uint32_t shName = 0;
75
76 void recordSection(InputSectionBase *isec);
77 void commitSection(InputSection *isec);
78 void finalizeInputSections();
79
80 // The following members are normally only used in linker scripts.
81 MemoryRegion *memRegion = nullptr;
82 MemoryRegion *lmaRegion = nullptr;
83 Expr addrExpr;
84 Expr alignExpr;
85 Expr lmaExpr;
86 Expr subalignExpr;
87 SmallVector<SectionCommand *, 0> commands;
88 SmallVector<StringRef, 0> phdrs;
89 std::optional<std::array<uint8_t, 4>> filler;
90 ConstraintKind constraint = ConstraintKind::NoConstraint;
91 std::string location;
92 std::string memoryRegionName;
93 std::string lmaRegionName;
94 bool nonAlloc = false;
95 bool typeIsSet = false;
96 bool expressionsUseSymbols = false;
97 bool usedInExpression = false;
98 bool inOverlay = false;
99
100 // Tracks whether the section has ever had an input section added to it, even
101 // if the section was later removed (e.g. because it is a synthetic section
102 // that wasn't needed). This is needed for orphan placement.
103 bool hasInputSections = false;
104
105 // The output section description is specified between DATA_SEGMENT_ALIGN and
106 // DATA_RELRO_END.
107 bool relro = false;
108
109 void finalize();
110 template <class ELFT>
111 void writeTo(uint8_t *buf, llvm::parallel::TaskGroup &tg);
112 // Check that the addends for dynamic relocations were written correctly.
113 void checkDynRelAddends(const uint8_t *bufStart);
114 template <class ELFT> void maybeCompress();
115
116 void sort(llvm::function_ref<int(InputSectionBase *s)> order);
117 void sortInitFini();
118 void sortCtorsDtors();
119
120 // Used for implementation of --compress-debug-sections and
121 // --compress-sections.
122 CompressedData compressed;
123
124private:
125 SmallVector<InputSection *, 0> storage;
126
127 std::array<uint8_t, 4> getFiller();
128};
129
130struct OutputDesc final : SectionCommand {
131 OutputSection osec;
132 OutputDesc(StringRef name, uint32_t type, uint64_t flags)
133 : SectionCommand(OutputSectionKind), osec(name, type, flags) {}
134
135 static bool classof(const SectionCommand *c) {
136 return c->kind == OutputSectionKind;
137 }
138};
139
140int getPriority(StringRef s);
141
142InputSection *getFirstInputSection(const OutputSection *os);
143llvm::ArrayRef<InputSection *>
144getInputSections(const OutputSection &os,
145 SmallVector<InputSection *, 0> &storage);
146
147// All output sections that are handled by the linker specially are
148// globally accessible. Writer initializes them, so don't use them
149// until Writer is initialized.
150struct Out {
151 static uint8_t *bufferStart;
152 static PhdrEntry *tlsPhdr;
153 static OutputSection *elfHeader;
154 static OutputSection *programHeaders;
155 static OutputSection *preinitArray;
156 static OutputSection *initArray;
157 static OutputSection *finiArray;
158};
159
160uint64_t getHeaderSize();
161
162LLVM_LIBRARY_VISIBILITY extern llvm::SmallVector<OutputSection *, 0>
163 outputSections;
164} // namespace lld::elf
165
166#endif
167

source code of lld/ELF/OutputSections.h