1 //===- OutputSections.h -----------------------------------------*- C++ -*-===//
2 //
3 //                             The LLVM Linker
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef LLD_ELF_OUTPUT_SECTIONS_H
11 #define LLD_ELF_OUTPUT_SECTIONS_H
12 
13 #include "Config.h"
14 #include "InputSection.h"
15 #include "Relocations.h"
16 
17 #include "lld/Core/LLVM.h"
18 #include "llvm/MC/StringTableBuilder.h"
19 #include "llvm/Object/ELF.h"
20 
21 namespace lld {
22 namespace elf {
23 
24 struct PhdrEntry;
25 class SymbolBody;
26 struct EhSectionPiece;
27 class EhInputSection;
28 class InputSection;
29 class InputSectionBase;
30 class MergeInputSection;
31 class OutputSection;
32 template <class ELFT> class ObjectFile;
33 template <class ELFT> class SharedFile;
34 class SharedSymbol;
35 class DefinedRegular;
36 
37 // This represents a section in an output file.
38 // It is composed of multiple InputSections.
39 // The writer creates multiple OutputSections and assign them unique,
40 // non-overlapping file offsets and VAs.
41 class OutputSection final : public SectionBase {
42 public:
43   OutputSection(StringRef Name, uint32_t Type, uint64_t Flags);
44 
45   static bool classof(const SectionBase *S) {
46     return S->kind() == SectionBase::Output;
47   }
48 
49   uint64_t getLMA() const { return Addr + LMAOffset; }
50   template <typename ELFT> void writeHeaderTo(typename ELFT::Shdr *SHdr);
51 
52   unsigned SectionIndex;
53   unsigned SortRank;
54 
55   uint32_t getPhdrFlags() const;
56 
57   void updateAlignment(uint32_t Val) {
58     if (Val > Alignment)
59       Alignment = Val;
60   }
61 
62   // Pointer to the first section in PT_LOAD segment, which this section
63   // also resides in. This field is used to correctly compute file offset
64   // of a section. When two sections share the same load segment, difference
65   // between their file offsets should be equal to difference between their
66   // virtual addresses. To compute some section offset we use the following
67   // formula: Off = Off_first + VA - VA_first.
68   OutputSection *FirstInPtLoad = nullptr;
69 
70   // Pointer to a relocation section for this section. Usually nullptr because
71   // we consume relocations, but if --emit-relocs is specified (which is rare),
72   // it may have a non-null value.
73   OutputSection *RelocationSection = nullptr;
74 
75   // The following fields correspond to Elf_Shdr members.
76   uint64_t Size = 0;
77   uint64_t Offset = 0;
78   uint64_t LMAOffset = 0;
79   uint64_t Addr = 0;
80   uint32_t ShName = 0;
81 
82   void addSection(InputSection *S);
83   void sort(std::function<int(InputSectionBase *S)> Order);
84   void sortInitFini();
85   void sortCtorsDtors();
86   void assignOffsets();
87   std::vector<InputSection *> Sections;
88 
89   // Used for implementation of --compress-debug-sections option.
90   std::vector<uint8_t> ZDebugHeader;
91   llvm::SmallVector<char, 1> CompressedData;
92 
93   // Location in the output buffer.
94   uint8_t *Loc = nullptr;
95 };
96 
97 // All output sections that are handled by the linker specially are
98 // globally accessible. Writer initializes them, so don't use them
99 // until Writer is initialized.
100 struct Out {
101   static uint8_t First;
102   static OutputSection *Opd;
103   static uint8_t *OpdBuf;
104   static PhdrEntry *TlsPhdr;
105   static OutputSection *DebugInfo;
106   static OutputSection *ElfHeader;
107   static OutputSection *ProgramHeaders;
108   static OutputSection *PreinitArray;
109   static OutputSection *InitArray;
110   static OutputSection *FiniArray;
111 };
112 
113 struct SectionKey {
114   StringRef Name;
115   uint64_t Flags;
116   uint32_t Alignment;
117 };
118 }
119 }
120 namespace llvm {
121 template <> struct DenseMapInfo<lld::elf::SectionKey> {
122   static lld::elf::SectionKey getEmptyKey();
123   static lld::elf::SectionKey getTombstoneKey();
124   static unsigned getHashValue(const lld::elf::SectionKey &Val);
125   static bool isEqual(const lld::elf::SectionKey &LHS,
126                       const lld::elf::SectionKey &RHS);
127 };
128 }
129 namespace lld {
130 namespace elf {
131 
132 // This class knows how to create an output section for a given
133 // input section. Output section type is determined by various
134 // factors, including input section's sh_flags, sh_type and
135 // linker scripts.
136 class OutputSectionFactory {
137 public:
138   OutputSectionFactory(std::vector<OutputSection *> &OutputSections);
139   ~OutputSectionFactory();
140 
141   void addInputSec(InputSectionBase *IS, StringRef OutsecName);
142   void addInputSec(InputSectionBase *IS, StringRef OutsecName,
143                    OutputSection *&Sec);
144 
145 private:
146   llvm::SmallDenseMap<SectionKey, OutputSection *> Map;
147   std::vector<OutputSection *> &OutputSections;
148 };
149 
150 uint64_t getHeaderSize();
151 void reportDiscarded(InputSectionBase *IS);
152 
153 extern std::vector<OutputSection *> OutputSections;
154 extern std::vector<OutputSectionCommand *> OutputSectionCommands;
155 } // namespace elf
156 } // namespace lld
157 
158 
159 #endif
160