1//===- ConcatOutputSection.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_CONCAT_OUTPUT_SECTION_H
10#define LLD_MACHO_CONCAT_OUTPUT_SECTION_H
11
12#include "InputSection.h"
13#include "OutputSection.h"
14#include "lld/Common/LLVM.h"
15#include "llvm/ADT/DenseMap.h"
16#include "llvm/ADT/MapVector.h"
17
18namespace lld::macho {
19
20class Defined;
21
22// Linking multiple files will inevitably mean resolving sections in different
23// files that are labeled with the same segment and section name. This class
24// contains all such sections and writes the data from each section sequentially
25// in the final binary.
26class ConcatOutputSection : public OutputSection {
27public:
28 explicit ConcatOutputSection(StringRef name)
29 : OutputSection(ConcatKind, name) {}
30
31 const ConcatInputSection *firstSection() const { return inputs.front(); }
32 const ConcatInputSection *lastSection() const { return inputs.back(); }
33 bool isNeeded() const override { return !inputs.empty(); }
34
35 // These accessors will only be valid after finalizing the section
36 uint64_t getSize() const override { return size; }
37 uint64_t getFileSize() const override { return fileSize; }
38
39 // Assign values to InputSection::outSecOff. In contrast to TextOutputSection,
40 // which does this in its implementation of `finalize()`, we can do this
41 // without `finalize()`'s sequential guarantees detailed in the block comment
42 // of `OutputSection::finalize()`.
43 virtual void finalizeContents();
44
45 void addInput(ConcatInputSection *input);
46 void writeTo(uint8_t *buf) const override;
47
48 static bool classof(const OutputSection *sec) {
49 return sec->kind() == ConcatKind;
50 }
51
52 static ConcatOutputSection *getOrCreateForInput(const InputSection *);
53
54 std::vector<ConcatInputSection *> inputs;
55
56protected:
57 size_t size = 0;
58 uint64_t fileSize = 0;
59 void finalizeOne(ConcatInputSection *);
60
61private:
62 void finalizeFlags(InputSection *input);
63};
64
65// ConcatOutputSections that contain code (text) require special handling to
66// support thunk insertion.
67class TextOutputSection : public ConcatOutputSection {
68public:
69 explicit TextOutputSection(StringRef name) : ConcatOutputSection(name) {}
70 void finalizeContents() override {}
71 void finalize() override;
72 bool needsThunks() const;
73 void writeTo(uint8_t *buf) const override;
74
75private:
76 uint64_t estimateStubsInRangeVA(size_t callIdx) const;
77
78 std::vector<ConcatInputSection *> thunks;
79};
80
81// We maintain one ThunkInfo per real function.
82//
83// The "active thunk" is represented by the sym/isec pair that
84// turns-over during finalize(): as the call-site address advances,
85// the active thunk goes out of branch-range, and we create a new
86// thunk to take its place.
87//
88// The remaining members -- bools and counters -- apply to the
89// collection of thunks associated with the real function.
90
91struct ThunkInfo {
92 // These denote the active thunk:
93 Defined *sym = nullptr; // private-extern symbol for active thunk
94 ConcatInputSection *isec = nullptr; // input section for active thunk
95
96 // The following values are cumulative across all thunks on this function
97 uint32_t callSiteCount = 0; // how many calls to the real function?
98 uint32_t callSitesUsed = 0; // how many call sites processed so-far?
99 uint32_t thunkCallCount = 0; // how many call sites went to thunk?
100 uint8_t sequence = 0; // how many thunks created so-far?
101};
102
103NamePair maybeRenameSection(NamePair key);
104
105// Output sections are added to output segments in iteration order
106// of ConcatOutputSection, so must have deterministic iteration order.
107extern llvm::MapVector<NamePair, ConcatOutputSection *> concatOutputSections;
108
109extern llvm::DenseMap<Symbol *, ThunkInfo> thunkMap;
110
111} // namespace lld::macho
112
113#endif
114

source code of lld/MachO/ConcatOutputSection.h