aboutsummaryrefslogtreecommitdiffstats
path: root/ELF/Thunks.cpp
blob: da2b136775132f6cea30fecaa14273535b0192a7 (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
//===- Thunks.cpp --------------------------------------------------------===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===---------------------------------------------------------------------===//
//
// This file contains Thunk subclasses.
//
// A thunk is a small piece of code written after an input section
// which is used to jump between "incompatible" functions
// such as MIPS PIC and non-PIC or ARM non-Thumb and Thumb functions.
//
// If a jump target is too far and its address doesn't fit to a
// short jump instruction, we need to create a thunk too, but we
// haven't supported it yet.
//
// i386 and x86-64 don't need thunks.
//
//===---------------------------------------------------------------------===//

#include "Thunks.h"
#include "Config.h"
#include "Error.h"
#include "InputSection.h"
#include "Memory.h"
#include "OutputSections.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include <cstdint>
#include <cstring>

using namespace llvm;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace llvm::ELF;

namespace lld {
namespace elf {

namespace {

// Specific ARM Thunk implementations. The naming convention is:
// Source State, TargetState, Target Requirement, ABS or PI, Range
class ARMV7ABSLongThunk final : public Thunk {
public:
  ARMV7ABSLongThunk(const SymbolBody &Dest) : Thunk(Dest) {}

  uint32_t size() const override { return 12; }
  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
  void addSymbols(ThunkSection &IS) override;
};

class ARMV7PILongThunk final : public Thunk {
public:
  ARMV7PILongThunk(const SymbolBody &Dest) : Thunk(Dest) {}

  uint32_t size() const override { return 16; }
  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
  void addSymbols(ThunkSection &IS) override;
};

class ThumbV7ABSLongThunk final : public Thunk {
public:
  ThumbV7ABSLongThunk(const SymbolBody &Dest) : Thunk(Dest) {
    this->alignment = 2;
  }

  uint32_t size() const override { return 10; }
  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
  void addSymbols(ThunkSection &IS) override;
};

class ThumbV7PILongThunk final : public Thunk {
public:
  ThumbV7PILongThunk(const SymbolBody &Dest) : Thunk(Dest) {
    this->alignment = 2;
  }

  uint32_t size() const override { return 12; }
  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
  void addSymbols(ThunkSection &IS) override;
};

// MIPS LA25 thunk
class MipsThunk final : public Thunk {
public:
  MipsThunk(const SymbolBody &Dest) : Thunk(Dest) {}

  uint32_t size() const override { return 16; }
  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
  void addSymbols(ThunkSection &IS) override;
  InputSection *getTargetInputSection() const override;
};

} // end anonymous namespace

// ARM Target Thunks
static uint64_t getARMThunkDestVA(const SymbolBody &S) {
  uint64_t V = S.isInPlt() ? S.getPltVA() : S.getVA();
  return SignExtend64<32>(V);
}

void ARMV7ABSLongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
  const uint8_t Data[] = {
      0x00, 0xc0, 0x00, 0xe3, // movw         ip,:lower16:S
      0x00, 0xc0, 0x40, 0xe3, // movt         ip,:upper16:S
      0x1c, 0xff, 0x2f, 0xe1, // bx   ip
  };
  uint64_t S = getARMThunkDestVA(Destination);
  memcpy(Buf, Data, sizeof(Data));
  Target->relocateOne(Buf, R_ARM_MOVW_ABS_NC, S);
  Target->relocateOne(Buf + 4, R_ARM_MOVT_ABS, S);
}

void ARMV7ABSLongThunk::addSymbols(ThunkSection &IS) {
  ThunkSym = addSyntheticLocal(
      Saver.save("__ARMv7ABSLongThunk_" + Destination.getName()), STT_FUNC,
      Offset, size(), &IS);
  addSyntheticLocal("$a", STT_NOTYPE, Offset, 0, &IS);
}

void ThumbV7ABSLongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
  const uint8_t Data[] = {
      0x40, 0xf2, 0x00, 0x0c, // movw         ip, :lower16:S
      0xc0, 0xf2, 0x00, 0x0c, // movt         ip, :upper16:S
      0x60, 0x47,             // bx   ip
  };
  uint64_t S = getARMThunkDestVA(Destination);
  memcpy(Buf, Data, sizeof(Data));
  Target->relocateOne(Buf, R_ARM_THM_MOVW_ABS_NC, S);
  Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_ABS, S);
}

void ThumbV7ABSLongThunk::addSymbols(ThunkSection &IS) {
  ThunkSym = addSyntheticLocal(
      Saver.save("__Thumbv7ABSLongThunk_" + Destination.getName()), STT_FUNC,
      Offset, size(), &IS);
  addSyntheticLocal("$t", STT_NOTYPE, Offset, 0, &IS);
}

void ARMV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
  const uint8_t Data[] = {
      0xf0, 0xcf, 0x0f, 0xe3, // P:  movw ip,:lower16:S - (P + (L1-P) +8)
      0x00, 0xc0, 0x40, 0xe3, //     movt ip,:upper16:S - (P + (L1-P+4) +8)
      0x0f, 0xc0, 0x8c, 0xe0, // L1: add ip, ip, pc
      0x1c, 0xff, 0x2f, 0xe1, //     bx r12
  };
  uint64_t S = getARMThunkDestVA(Destination);
  uint64_t P = ThunkSym->getVA();
  memcpy(Buf, Data, sizeof(Data));
  Target->relocateOne(Buf, R_ARM_MOVW_PREL_NC, S - P - 16);
  Target->relocateOne(Buf + 4, R_ARM_MOVT_PREL, S - P - 12);
}

void ARMV7PILongThunk::addSymbols(ThunkSection &IS) {
  ThunkSym = addSyntheticLocal(
      Saver.save("__ARMV7PILongThunk_" + Destination.getName()), STT_FUNC,
      Offset, size(), &IS);
  addSyntheticLocal("$a", STT_NOTYPE, Offset, 0, &IS);
}

void ThumbV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
  const uint8_t Data[] = {
      0x4f, 0xf6, 0xf4, 0x7c, // P:  movw ip,:lower16:S - (P + (L1-P) + 4)
      0xc0, 0xf2, 0x00, 0x0c, //     movt ip,:upper16:S - (P + (L1-P+4) + 4)
      0xfc, 0x44,             // L1: add  r12, pc
      0x60, 0x47,             //     bx   r12
  };
  uint64_t S = getARMThunkDestVA(Destination);
  uint64_t P = ThunkSym->getVA();
  memcpy(Buf, Data, sizeof(Data));
  Target->relocateOne(Buf, R_ARM_THM_MOVW_PREL_NC, S - P - 12);
  Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_PREL, S - P - 8);
}

void ThumbV7PILongThunk::addSymbols(ThunkSection &IS) {
  ThunkSym = addSyntheticLocal(
      Saver.save("__ThumbV7PILongThunk_" + Destination.getName()), STT_FUNC,
      Offset, size(), &IS);
  addSyntheticLocal("$t", STT_NOTYPE, Offset, 0, &IS);
}

// Write MIPS LA25 thunk code to call PIC function from the non-PIC one.
void MipsThunk::writeTo(uint8_t *Buf, ThunkSection &) const {
  uint64_t S = this->Destination.getVA();
  write32(Buf, 0x3c190000, Config->Endianness);                // lui   $25, %hi(func)
  write32(Buf + 4, 0x08000000 | (S >> 2), Config->Endianness); // j     func
  write32(Buf + 8, 0x27390000, Config->Endianness);            // addiu $25, $25, %lo(func)
  write32(Buf + 12, 0x00000000, Config->Endianness);           // nop
  Target->relocateOne(Buf, R_MIPS_HI16, S);
  Target->relocateOne(Buf + 8, R_MIPS_LO16, S);
}

void MipsThunk::addSymbols(ThunkSection &IS) {
  ThunkSym =
      addSyntheticLocal(Saver.save("__LA25Thunk_" + Destination.getName()),
                        STT_FUNC, Offset, size(), &IS);
}

InputSection *MipsThunk::getTargetInputSection() const {
  auto *DR = dyn_cast<DefinedRegular>(&Destination);
  return dyn_cast<InputSection>(DR->Section);
}

Thunk::Thunk(const SymbolBody &D) : Destination(D), Offset(0) {}

Thunk::~Thunk() = default;

// Creates a thunk for Thumb-ARM interworking.
static Thunk *addThunkArm(uint32_t Reloc, SymbolBody &S) {
  // ARM relocations need ARM to Thumb interworking Thunks.
  // Thumb relocations need Thumb to ARM relocations.
  // Use position independent Thunks if we require position independent code.
  switch (Reloc) {
  case R_ARM_PC24:
  case R_ARM_PLT32:
  case R_ARM_JUMP24:
    if (Config->Pic)
      return make<ARMV7PILongThunk>(S);
    return make<ARMV7ABSLongThunk>(S);
  case R_ARM_THM_JUMP19:
  case R_ARM_THM_JUMP24:
    if (Config->Pic)
      return make<ThumbV7PILongThunk>(S);
    return make<ThumbV7ABSLongThunk>(S);
  }
  fatal("unrecognized relocation type");
}

static Thunk *addThunkMips(SymbolBody &S) {
  return make<MipsThunk>(S);
}

Thunk *addThunk(uint32_t RelocType, SymbolBody &S) {
  if (Config->EMachine == EM_ARM)
    return addThunkArm(RelocType, S);
  else if (Config->EMachine == EM_MIPS)
    return addThunkMips(S);
  llvm_unreachable("add Thunk only supported for ARM and Mips");
  return nullptr;
}

} // end namespace elf
} // end namespace lld