lld/MachO/OutputSection.h

   1 //===- OutputSection.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_MACHO_OUTPUT_SECTION_H
  10 #define LLD_MACHO_OUTPUT_SECTION_H
  11
  12 #include "Symbols.h"
  13 #include "lld/Common/LLVM.h"
  14 #include "llvm/ADT/DenseMap.h"
  15 #include "llvm/ADT/TinyPtrVector.h"
  16
  17 #include <limits>
  18
  19 namespace lld::macho {
  20
  21 class Defined;
  22 class InputSection;
  23 class OutputSegment;
  24
  25 // The default order value for OutputSections that are not constructed from
  26 // InputSections (i.e. SyntheticSections). We make it less than INT_MAX in order
  27 // not to conflict with the ordering of zerofill sections, which must always be
  28 // placed at the end of their segment.
  29 constexpr int UnspecifiedInputOrder = std::numeric_limits<int>::max() - 1024;
  30
  31 // Output sections represent the finalized sections present within the final
  32 // linked executable. They can represent special sections (like the symbol
  33 // table), or represent coalesced sections from the various inputs given to the
  34 // linker with the same segment / section name.
  35 class OutputSection {
  36 public:
  37   enum Kind {
  38     ConcatKind,
  39     SyntheticKind,
  40   };
  41
  42   OutputSection(Kind kind, StringRef name) : name(name), sectionKind(kind) {}
  43   virtual ~OutputSection() = default;
  44   Kind kind() const { return sectionKind; }
  45
  46   // These accessors will only be valid after finalizing the section.
  47   uint64_t getSegmentOffset() const;
  48
  49   // How much space the section occupies in the address space.
  50   virtual uint64_t getSize() const = 0;
  51   // How much space the section occupies in the file. Most sections are copied
  52   // as-is so their file size is the same as their address space size.
  53   virtual uint64_t getFileSize() const { return getSize(); }
  54
  55   // Hidden sections omit header content, but body content may still be present.
  56   virtual bool isHidden() const { return false; }
  57   // Unneeded sections are omitted entirely (header and body).
  58   virtual bool isNeeded() const { return true; }
  59
  60   // The implementations of this method can assume that it is only called right
  61   // before addresses get assigned to this particular OutputSection. In
  62   // particular, this means that it gets called only after addresses have been
  63   // assigned to output sections that occur earlier in the output binary.
  64   // Naturally, this means different sections' finalize() methods cannot execute
  65   // concurrently with each other. As such, avoid using this method for
  66   // operations that do not require this strict sequential guarantee.
  67   //
  68   // Operations that need to occur late in the linking process, but which do not
  69   // need the sequential guarantee, should be named `finalizeContents()`. See
  70   // e.g. LinkEditSection::finalizeContents() and
  71   // CStringSection::finalizeContents().
  72   virtual void finalize() {}
  73
  74   virtual void writeTo(uint8_t *buf) const = 0;
  75
  76   // Handle section$start$ and section$end$ symbols.
  77   void assignAddressesToStartEndSymbols();
  78
  79   StringRef name;
  80   llvm::TinyPtrVector<Defined *> sectionStartSymbols;
  81   llvm::TinyPtrVector<Defined *> sectionEndSymbols;
  82   OutputSegment *parent = nullptr;
  83   // For output sections that don't have explicit ordering requirements, their
  84   // output order should be based on the order of the input sections they
  85   // contain.
  86   int inputOrder = UnspecifiedInputOrder;
  87
  88   uint32_t index = 0;
  89   uint64_t addr = 0;
  90   uint64_t fileOff = 0;
  91   uint32_t align = 1;
  92   uint32_t flags = 0;
  93   uint32_t reserved1 = 0;
  94   uint32_t reserved2 = 0;
  95
  96 private:
  97   Kind sectionKind;
  98 };
  99
 100 } // namespace lld::macho
 101
 102 #endif