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
19namespace lld::macho {
20
21class Defined;
22class InputSection;
23class 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.
29constexpr 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.
35class OutputSection {
36public:
37 enum Kind {
38 ConcatKind,
39 SyntheticKind,
40 TextKind,
41 };
42
43 OutputSection(Kind kind, StringRef name) : name(name), sectionKind(kind) {}
44 virtual ~OutputSection() = default;
45 Kind kind() const { return sectionKind; }
46
47 // These accessors will only be valid after finalizing the section.
48 uint64_t getSegmentOffset() const;
49
50 // How much space the section occupies in the address space.
51 virtual uint64_t getSize() const = 0;
52 // How much space the section occupies in the file. Most sections are copied
53 // as-is so their file size is the same as their address space size.
54 virtual uint64_t getFileSize() const { return getSize(); }
55
56 // Hidden sections omit header content, but body content may still be present.
57 virtual bool isHidden() const { return false; }
58 // Unneeded sections are omitted entirely (header and body).
59 virtual bool isNeeded() const { return true; }
60
61 // The implementations of this method can assume that it is only called right
62 // before addresses get assigned to this particular OutputSection. In
63 // particular, this means that it gets called only after addresses have been
64 // assigned to output sections that occur earlier in the output binary.
65 // Naturally, this means different sections' finalize() methods cannot execute
66 // concurrently with each other. As such, avoid using this method for
67 // operations that do not require this strict sequential guarantee.
68 //
69 // Operations that need to occur late in the linking process, but which do not
70 // need the sequential guarantee, should be named `finalizeContents()`. See
71 // e.g. LinkEditSection::finalizeContents() and
72 // CStringSection::finalizeContents().
73 virtual void finalize() {}
74
75 virtual void writeTo(uint8_t *buf) const = 0;
76
77 // Handle section$start$ and section$end$ symbols.
78 void assignAddressesToStartEndSymbols();
79
80 StringRef name;
81 llvm::TinyPtrVector<Defined *> sectionStartSymbols;
82 llvm::TinyPtrVector<Defined *> sectionEndSymbols;
83 OutputSegment *parent = nullptr;
84 // For output sections that don't have explicit ordering requirements, their
85 // output order should be based on the order of the input sections they
86 // contain.
87 int inputOrder = UnspecifiedInputOrder;
88
89 uint32_t index = 0;
90 uint64_t addr = 0;
91 uint64_t fileOff = 0;
92 uint32_t align = 1;
93 uint32_t flags = 0;
94 uint32_t reserved1 = 0;
95 uint32_t reserved2 = 0;
96
97private:
98 Kind sectionKind;
99};
100
101} // namespace lld::macho
102
103#endif
104