aboutsummaryrefslogtreecommitdiffstats
path: root/ELF/InputSection.h
blob: 3a974074e0e51a5cc9330460f5630fff3b1f2ee8 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
//===- InputSection.h -------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLD_ELF_INPUT_SECTION_H
#define LLD_ELF_INPUT_SECTION_H

#include "Config.h"
#include "Relocations.h"
#include "Thunks.h"
#include "lld/Common/LLVM.h"
#include "llvm/ADT/CachedHashString.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Object/ELF.h"

namespace lld {
namespace elf {

class Symbol;
struct SectionPiece;

class Defined;
struct Partition;
class SyntheticSection;
class MergeSyntheticSection;
template <class ELFT> class ObjFile;
class OutputSection;

extern std::vector<Partition> partitions;

// This is the base class of all sections that lld handles. Some are sections in
// input files, some are sections in the produced output file and some exist
// just as a convenience for implementing special ways of combining some
// sections.
class SectionBase {
public:
  enum Kind { Regular, EHFrame, Merge, Synthetic, Output };

  Kind kind() const { return (Kind)sectionKind; }

  StringRef name;

  // This pointer points to the "real" instance of this instance.
  // Usually Repl == this. However, if ICF merges two sections,
  // Repl pointer of one section points to another section. So,
  // if you need to get a pointer to this instance, do not use
  // this but instead this->Repl.
  SectionBase *repl;

  unsigned sectionKind : 3;

  // The next three bit fields are only used by InputSectionBase, but we
  // put them here so the struct packs better.

  // True if this section has already been placed to a linker script
  // output section. This is needed because, in a linker script, you
  // can refer to the same section more than once. For example, in
  // the following linker script,
  //
  //   .foo : { *(.text) }
  //   .bar : { *(.text) }
  //
  // .foo takes all .text sections, and .bar becomes empty. To achieve
  // this, we need to memorize whether a section has been placed or
  // not for each input section.
  unsigned assigned : 1;

  unsigned bss : 1;

  // Set for sections that should not be folded by ICF.
  unsigned keepUnique : 1;

  // The 1-indexed partition that this section is assigned to by the garbage
  // collector, or 0 if this section is dead. Normally there is only one
  // partition, so this will either be 0 or 1.
  uint8_t partition;
  elf::Partition &getPartition() const;

  // These corresponds to the fields in Elf_Shdr.
  uint32_t alignment;
  uint64_t flags;
  uint64_t entsize;
  uint32_t type;
  uint32_t link;
  uint32_t info;

  OutputSection *getOutputSection();
  const OutputSection *getOutputSection() const {
    return const_cast<SectionBase *>(this)->getOutputSection();
  }

  // Translate an offset in the input section to an offset in the output
  // section.
  uint64_t getOffset(uint64_t offset) const;

  uint64_t getVA(uint64_t offset = 0) const;

  bool isLive() const { return partition != 0; }
  void markLive() { partition = 1; }
  void markDead() { partition = 0; }

protected:
  SectionBase(Kind sectionKind, StringRef name, uint64_t flags,
              uint64_t entsize, uint64_t alignment, uint32_t type,
              uint32_t info, uint32_t link)
      : name(name), repl(this), sectionKind(sectionKind), assigned(false),
        bss(false), keepUnique(false), partition(0), alignment(alignment),
        flags(flags), entsize(entsize), type(type), link(link), info(info) {}
};

// This corresponds to a section of an input file.
class InputSectionBase : public SectionBase {
public:
  template <class ELFT>
  InputSectionBase(ObjFile<ELFT> &file, const typename ELFT::Shdr &header,
                   StringRef name, Kind sectionKind);

  InputSectionBase(InputFile *file, uint64_t flags, uint32_t type,
                   uint64_t entsize, uint32_t link, uint32_t info,
                   uint32_t alignment, ArrayRef<uint8_t> data, StringRef name,
                   Kind sectionKind);

  static bool classof(const SectionBase *s) { return s->kind() != Output; }

  // Relocations that refer to this section.
  unsigned numRelocations : 31;
  unsigned areRelocsRela : 1;
  const void *firstRelocation = nullptr;

  // The file which contains this section. Its dynamic type is always
  // ObjFile<ELFT>, but in order to avoid ELFT, we use InputFile as
  // its static type.
  InputFile *file;

  template <class ELFT> ObjFile<ELFT> *getFile() const {
    return cast_or_null<ObjFile<ELFT>>(file);
  }

  ArrayRef<uint8_t> data() const {
    if (uncompressedSize >= 0)
      uncompress();
    return rawData;
  }

  uint64_t getOffsetInFile() const;

  // Input sections are part of an output section. Special sections
  // like .eh_frame and merge sections are first combined into a
  // synthetic section that is then added to an output section. In all
  // cases this points one level up.
  SectionBase *parent = nullptr;

  template <class ELFT> ArrayRef<typename ELFT::Rel> rels() const {
    assert(!areRelocsRela);
    return llvm::makeArrayRef(
        static_cast<const typename ELFT::Rel *>(firstRelocation),
        numRelocations);
  }

  template <class ELFT> ArrayRef<typename ELFT::Rela> relas() const {
    assert(areRelocsRela);
    return llvm::makeArrayRef(
        static_cast<const typename ELFT::Rela *>(firstRelocation),
        numRelocations);
  }

  // InputSections that are dependent on us (reverse dependency for GC)
  llvm::TinyPtrVector<InputSection *> dependentSections;

  // Returns the size of this section (even if this is a common or BSS.)
  size_t getSize() const;

  InputSection *getLinkOrderDep() const;

  // Get the function symbol that encloses this offset from within the
  // section.
  template <class ELFT>
  Defined *getEnclosingFunction(uint64_t offset);

  // Returns a source location string. Used to construct an error message.
  template <class ELFT> std::string getLocation(uint64_t offset);
  std::string getSrcMsg(const Symbol &sym, uint64_t offset);
  std::string getObjMsg(uint64_t offset);

  // Each section knows how to relocate itself. These functions apply
  // relocations, assuming that Buf points to this section's copy in
  // the mmap'ed output buffer.
  template <class ELFT> void relocate(uint8_t *buf, uint8_t *bufEnd);
  void relocateAlloc(uint8_t *buf, uint8_t *bufEnd);

  // The native ELF reloc data type is not very convenient to handle.
  // So we convert ELF reloc records to our own records in Relocations.cpp.
  // This vector contains such "cooked" relocations.
  std::vector<Relocation> relocations;

  // A function compiled with -fsplit-stack calling a function
  // compiled without -fsplit-stack needs its prologue adjusted. Find
  // such functions and adjust their prologues.  This is very similar
  // to relocation. See https://gcc.gnu.org/wiki/SplitStacks for more
  // information.
  template <typename ELFT>
  void adjustSplitStackFunctionPrologues(uint8_t *buf, uint8_t *end);


  template <typename T> llvm::ArrayRef<T> getDataAs() const {
    size_t s = data().size();
    assert(s % sizeof(T) == 0);
    return llvm::makeArrayRef<T>((const T *)data().data(), s / sizeof(T));
  }

protected:
  void parseCompressedHeader();
  void uncompress() const;

  mutable ArrayRef<uint8_t> rawData;

  // This field stores the uncompressed size of the compressed data in rawData,
  // or -1 if rawData is not compressed (either because the section wasn't
  // compressed in the first place, or because we ended up uncompressing it).
  // Since the feature is not used often, this is usually -1.
  mutable int64_t uncompressedSize = -1;
};

// SectionPiece represents a piece of splittable section contents.
// We allocate a lot of these and binary search on them. This means that they
// have to be as compact as possible, which is why we don't store the size (can
// be found by looking at the next one).
struct SectionPiece {
  SectionPiece(size_t off, uint32_t hash, bool live)
      : inputOff(off), live(live || !config->gcSections), hash(hash >> 1) {}

  uint32_t inputOff;
  uint32_t live : 1;
  uint32_t hash : 31;
  uint64_t outputOff = 0;
};

static_assert(sizeof(SectionPiece) == 16, "SectionPiece is too big");

// This corresponds to a SHF_MERGE section of an input file.
class MergeInputSection : public InputSectionBase {
public:
  template <class ELFT>
  MergeInputSection(ObjFile<ELFT> &f, const typename ELFT::Shdr &header,
                    StringRef name);
  MergeInputSection(uint64_t flags, uint32_t type, uint64_t entsize,
                    ArrayRef<uint8_t> data, StringRef name);

  static bool classof(const SectionBase *s) { return s->kind() == Merge; }
  void splitIntoPieces();

  // Translate an offset in the input section to an offset in the parent
  // MergeSyntheticSection.
  uint64_t getParentOffset(uint64_t offset) const;

  // Splittable sections are handled as a sequence of data
  // rather than a single large blob of data.
  std::vector<SectionPiece> pieces;

  // Returns I'th piece's data. This function is very hot when
  // string merging is enabled, so we want to inline.
  LLVM_ATTRIBUTE_ALWAYS_INLINE
  llvm::CachedHashStringRef getData(size_t i) const {
    size_t begin = pieces[i].inputOff;
    size_t end =
        (pieces.size() - 1 == i) ? data().size() : pieces[i + 1].inputOff;
    return {toStringRef(data().slice(begin, end - begin)), pieces[i].hash};
  }

  // Returns the SectionPiece at a given input section offset.
  SectionPiece *getSectionPiece(uint64_t offset);
  const SectionPiece *getSectionPiece(uint64_t offset) const {
    return const_cast<MergeInputSection *>(this)->getSectionPiece(offset);
  }

  SyntheticSection *getParent() const;

private:
  void splitStrings(ArrayRef<uint8_t> a, size_t size);
  void splitNonStrings(ArrayRef<uint8_t> a, size_t size);
};

struct EhSectionPiece {
  EhSectionPiece(size_t off, InputSectionBase *sec, uint32_t size,
                 unsigned firstRelocation)
      : inputOff(off), sec(sec), size(size), firstRelocation(firstRelocation) {}

  ArrayRef<uint8_t> data() {
    return {sec->data().data() + this->inputOff, size};
  }

  size_t inputOff;
  ssize_t outputOff = -1;
  InputSectionBase *sec;
  uint32_t size;
  unsigned firstRelocation;
};

// This corresponds to a .eh_frame section of an input file.
class EhInputSection : public InputSectionBase {
public:
  template <class ELFT>
  EhInputSection(ObjFile<ELFT> &f, const typename ELFT::Shdr &header,
                 StringRef name);
  static bool classof(const SectionBase *s) { return s->kind() == EHFrame; }
  template <class ELFT> void split();
  template <class ELFT, class RelTy> void split(ArrayRef<RelTy> rels);

  // Splittable sections are handled as a sequence of data
  // rather than a single large blob of data.
  std::vector<EhSectionPiece> pieces;

  SyntheticSection *getParent() const;
};

// This is a section that is added directly to an output section
// instead of needing special combination via a synthetic section. This
// includes all input sections with the exceptions of SHF_MERGE and
// .eh_frame. It also includes the synthetic sections themselves.
class InputSection : public InputSectionBase {
public:
  InputSection(InputFile *f, uint64_t flags, uint32_t type, uint32_t alignment,
               ArrayRef<uint8_t> data, StringRef name, Kind k = Regular);
  template <class ELFT>
  InputSection(ObjFile<ELFT> &f, const typename ELFT::Shdr &header,
               StringRef name);

  // Write this section to a mmap'ed file, assuming Buf is pointing to
  // beginning of the output section.
  template <class ELFT> void writeTo(uint8_t *buf);

  uint64_t getOffset(uint64_t offset) const { return outSecOff + offset; }

  OutputSection *getParent() const;

  // This variable has two usages. Initially, it represents an index in the
  // OutputSection's InputSection list, and is used when ordering SHF_LINK_ORDER
  // sections. After assignAddresses is called, it represents the offset from
  // the beginning of the output section this section was assigned to.
  uint64_t outSecOff = 0;

  static bool classof(const SectionBase *s);

  InputSectionBase *getRelocatedSection() const;

  template <class ELFT, class RelTy>
  void relocateNonAlloc(uint8_t *buf, llvm::ArrayRef<RelTy> rels);

  // Used by ICF.
  uint32_t eqClass[2] = {0, 0};

  // Called by ICF to merge two input sections.
  void replace(InputSection *other);

  static InputSection discarded;

private:
  template <class ELFT, class RelTy>
  void copyRelocations(uint8_t *buf, llvm::ArrayRef<RelTy> rels);

  template <class ELFT> void copyShtGroup(uint8_t *buf);
};

// The list of all input sections.
extern std::vector<InputSectionBase *> inputSections;

} // namespace elf

std::string toString(const elf::InputSectionBase *);
} // namespace lld

#endif