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 20 namespace lld::elf { 21 22 struct PhdrEntry; 23 24 struct 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. 36 class OutputSection final : public SectionBase { 37 public: 38 OutputSection(StringRef name, uint32_t type, uint64_t flags); 39 classof(const SectionBase * s)40 static bool classof(const SectionBase *s) { 41 return s->kind() == SectionBase::Output; 42 } 43 getLMA()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(LinkerScript *script = nullptr); 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 88 // Used by non-alloc SHT_CREL to hold the header and content byte stream. 89 uint64_t crelHeader = 0; 90 SmallVector<char, 0> crelBody; 91 92 SmallVector<SectionCommand *, 0> commands; 93 SmallVector<StringRef, 0> phdrs; 94 std::optional<std::array<uint8_t, 4>> filler; 95 ConstraintKind constraint = ConstraintKind::NoConstraint; 96 std::string location; 97 std::string memoryRegionName; 98 std::string lmaRegionName; 99 bool nonAlloc = false; 100 bool typeIsSet = false; 101 bool expressionsUseSymbols = false; 102 bool usedInExpression = false; 103 bool inOverlay = false; 104 105 // Tracks whether the section has ever had an input section added to it, even 106 // if the section was later removed (e.g. because it is a synthetic section 107 // that wasn't needed). This is needed for orphan placement. 108 bool hasInputSections = false; 109 110 // The output section description is specified between DATA_SEGMENT_ALIGN and 111 // DATA_RELRO_END. 112 bool relro = false; 113 114 template <bool is64> void finalizeNonAllocCrel(); 115 void finalize(); 116 template <class ELFT> 117 void writeTo(uint8_t *buf, llvm::parallel::TaskGroup &tg); 118 // Check that the addends for dynamic relocations were written correctly. 119 void checkDynRelAddends(const uint8_t *bufStart); 120 template <class ELFT> void maybeCompress(); 121 122 void sort(llvm::function_ref<int(InputSectionBase *s)> order); 123 void sortInitFini(); 124 void sortCtorsDtors(); 125 126 // Used for implementation of --compress-debug-sections and 127 // --compress-sections. 128 CompressedData compressed; 129 130 private: 131 SmallVector<InputSection *, 0> storage; 132 133 std::array<uint8_t, 4> getFiller(); 134 }; 135 136 struct OutputDesc final : SectionCommand { 137 OutputSection osec; OutputDescfinal138 OutputDesc(StringRef name, uint32_t type, uint64_t flags) 139 : SectionCommand(OutputSectionKind), osec(name, type, flags) {} 140 classoffinal141 static bool classof(const SectionCommand *c) { 142 return c->kind == OutputSectionKind; 143 } 144 }; 145 146 int getPriority(StringRef s); 147 148 InputSection *getFirstInputSection(const OutputSection *os); 149 llvm::ArrayRef<InputSection *> 150 getInputSections(const OutputSection &os, 151 SmallVector<InputSection *, 0> &storage); 152 153 // All output sections that are handled by the linker specially are 154 // globally accessible. Writer initializes them, so don't use them 155 // until Writer is initialized. 156 struct Out { 157 static uint8_t *bufferStart; 158 static PhdrEntry *tlsPhdr; 159 static OutputSection *elfHeader; 160 static OutputSection *programHeaders; 161 static OutputSection *preinitArray; 162 static OutputSection *initArray; 163 static OutputSection *finiArray; 164 }; 165 166 uint64_t getHeaderSize(); 167 168 LLVM_LIBRARY_VISIBILITY extern llvm::SmallVector<OutputSection *, 0> 169 outputSections; 170 } // namespace lld::elf 171 172 #endif 173