1//===-- X86ELFObjectWriter.cpp - X86 ELF Writer ---------------------------===//
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#include "MCTargetDesc/X86FixupKinds.h"
10#include "MCTargetDesc/X86MCTargetDesc.h"
11#include "llvm/BinaryFormat/ELF.h"
12#include "llvm/MC/MCAsmInfo.h"
13#include "llvm/MC/MCContext.h"
14#include "llvm/MC/MCELFObjectWriter.h"
15#include "llvm/MC/MCExpr.h"
16#include "llvm/MC/MCFixup.h"
17#include "llvm/MC/MCObjectWriter.h"
18#include "llvm/MC/MCValue.h"
19#include "llvm/Support/ErrorHandling.h"
20#include <cassert>
21#include <cstdint>
22
23using namespace llvm;
24
25namespace {
26
27class X86ELFObjectWriter : public MCELFObjectTargetWriter {
28public:
29  X86ELFObjectWriter(bool IsELF64, uint8_t OSABI, uint16_t EMachine);
30  ~X86ELFObjectWriter() override = default;
31
32protected:
33  unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
34                        const MCFixup &Fixup, bool IsPCRel) const override;
35};
36
37} // end anonymous namespace
38
39X86ELFObjectWriter::X86ELFObjectWriter(bool IsELF64, uint8_t OSABI,
40                                       uint16_t EMachine)
41    : MCELFObjectTargetWriter(IsELF64, OSABI, EMachine,
42                              // Only i386 and IAMCU use Rel instead of RelA.
43                              /*HasRelocationAddend*/
44                              (EMachine != ELF::EM_386) &&
45                                  (EMachine != ELF::EM_IAMCU)) {}
46
47enum X86_64RelType { RT64_NONE, RT64_64, RT64_32, RT64_32S, RT64_16, RT64_8 };
48
49static X86_64RelType getType64(MCFixupKind Kind,
50                               MCSymbolRefExpr::VariantKind &Modifier,
51                               bool &IsPCRel) {
52  switch (unsigned(Kind)) {
53  default:
54    llvm_unreachable("Unimplemented");
55  case FK_NONE:
56    return RT64_NONE;
57  case X86::reloc_global_offset_table8:
58    Modifier = MCSymbolRefExpr::VK_GOT;
59    IsPCRel = true;
60    return RT64_64;
61  case FK_Data_8:
62    return RT64_64;
63  case X86::reloc_signed_4byte:
64  case X86::reloc_signed_4byte_relax:
65    if (Modifier == MCSymbolRefExpr::VK_None && !IsPCRel)
66      return RT64_32S;
67    return RT64_32;
68  case X86::reloc_global_offset_table:
69    Modifier = MCSymbolRefExpr::VK_GOT;
70    IsPCRel = true;
71    return RT64_32;
72  case FK_Data_4:
73  case FK_PCRel_4:
74  case X86::reloc_riprel_4byte:
75  case X86::reloc_riprel_4byte_relax:
76  case X86::reloc_riprel_4byte_relax_rex:
77  case X86::reloc_riprel_4byte_movq_load:
78    return RT64_32;
79  case X86::reloc_branch_4byte_pcrel:
80    Modifier = MCSymbolRefExpr::VK_PLT;
81    return RT64_32;
82  case FK_PCRel_2:
83  case FK_Data_2:
84    return RT64_16;
85  case FK_PCRel_1:
86  case FK_Data_1:
87    return RT64_8;
88  }
89}
90
91static void checkIs32(MCContext &Ctx, SMLoc Loc, X86_64RelType Type) {
92  if (Type != RT64_32)
93    Ctx.reportError(Loc,
94                    "32 bit reloc applied to a field with a different size");
95}
96
97static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
98                               MCSymbolRefExpr::VariantKind Modifier,
99                               X86_64RelType Type, bool IsPCRel,
100                               MCFixupKind Kind) {
101  switch (Modifier) {
102  default:
103    llvm_unreachable("Unimplemented");
104  case MCSymbolRefExpr::VK_None:
105  case MCSymbolRefExpr::VK_X86_ABS8:
106    switch (Type) {
107    case RT64_NONE:
108      if (Modifier == MCSymbolRefExpr::VK_None)
109        return ELF::R_X86_64_NONE;
110      llvm_unreachable("Unimplemented");
111    case RT64_64:
112      return IsPCRel ? ELF::R_X86_64_PC64 : ELF::R_X86_64_64;
113    case RT64_32:
114      return IsPCRel ? ELF::R_X86_64_PC32 : ELF::R_X86_64_32;
115    case RT64_32S:
116      return ELF::R_X86_64_32S;
117    case RT64_16:
118      return IsPCRel ? ELF::R_X86_64_PC16 : ELF::R_X86_64_16;
119    case RT64_8:
120      return IsPCRel ? ELF::R_X86_64_PC8 : ELF::R_X86_64_8;
121    }
122    llvm_unreachable("unexpected relocation type!");
123  case MCSymbolRefExpr::VK_GOT:
124    switch (Type) {
125    case RT64_64:
126      return IsPCRel ? ELF::R_X86_64_GOTPC64 : ELF::R_X86_64_GOT64;
127    case RT64_32:
128      return IsPCRel ? ELF::R_X86_64_GOTPC32 : ELF::R_X86_64_GOT32;
129    case RT64_32S:
130    case RT64_16:
131    case RT64_8:
132    case RT64_NONE:
133      llvm_unreachable("Unimplemented");
134    }
135    llvm_unreachable("unexpected relocation type!");
136  case MCSymbolRefExpr::VK_GOTOFF:
137    assert(Type == RT64_64);
138    assert(!IsPCRel);
139    return ELF::R_X86_64_GOTOFF64;
140  case MCSymbolRefExpr::VK_TPOFF:
141    assert(!IsPCRel);
142    switch (Type) {
143    case RT64_64:
144      return ELF::R_X86_64_TPOFF64;
145    case RT64_32:
146      return ELF::R_X86_64_TPOFF32;
147    case RT64_32S:
148    case RT64_16:
149    case RT64_8:
150    case RT64_NONE:
151      llvm_unreachable("Unimplemented");
152    }
153    llvm_unreachable("unexpected relocation type!");
154  case MCSymbolRefExpr::VK_DTPOFF:
155    assert(!IsPCRel);
156    switch (Type) {
157    case RT64_64:
158      return ELF::R_X86_64_DTPOFF64;
159    case RT64_32:
160      return ELF::R_X86_64_DTPOFF32;
161    case RT64_32S:
162    case RT64_16:
163    case RT64_8:
164    case RT64_NONE:
165      llvm_unreachable("Unimplemented");
166    }
167    llvm_unreachable("unexpected relocation type!");
168  case MCSymbolRefExpr::VK_SIZE:
169    assert(!IsPCRel);
170    switch (Type) {
171    case RT64_64:
172      return ELF::R_X86_64_SIZE64;
173    case RT64_32:
174      return ELF::R_X86_64_SIZE32;
175    case RT64_32S:
176    case RT64_16:
177    case RT64_8:
178    case RT64_NONE:
179      llvm_unreachable("Unimplemented");
180    }
181    llvm_unreachable("unexpected relocation type!");
182  case MCSymbolRefExpr::VK_TLSCALL:
183    return ELF::R_X86_64_TLSDESC_CALL;
184  case MCSymbolRefExpr::VK_TLSDESC:
185    return ELF::R_X86_64_GOTPC32_TLSDESC;
186  case MCSymbolRefExpr::VK_TLSGD:
187    checkIs32(Ctx, Loc, Type);
188    return ELF::R_X86_64_TLSGD;
189  case MCSymbolRefExpr::VK_GOTTPOFF:
190    checkIs32(Ctx, Loc, Type);
191    return ELF::R_X86_64_GOTTPOFF;
192  case MCSymbolRefExpr::VK_TLSLD:
193    checkIs32(Ctx, Loc, Type);
194    return ELF::R_X86_64_TLSLD;
195  case MCSymbolRefExpr::VK_PLT:
196    checkIs32(Ctx, Loc, Type);
197    return ELF::R_X86_64_PLT32;
198  case MCSymbolRefExpr::VK_GOTPCREL:
199    checkIs32(Ctx, Loc, Type);
200    // Older versions of ld.bfd/ld.gold/lld
201    // do not support GOTPCRELX/REX_GOTPCRELX,
202    // and we want to keep back-compatibility.
203    if (!Ctx.getAsmInfo()->canRelaxRelocations())
204      return ELF::R_X86_64_GOTPCREL;
205    switch (unsigned(Kind)) {
206    default:
207      return ELF::R_X86_64_GOTPCREL;
208    case X86::reloc_riprel_4byte_relax:
209      return ELF::R_X86_64_GOTPCRELX;
210    case X86::reloc_riprel_4byte_relax_rex:
211    case X86::reloc_riprel_4byte_movq_load:
212      return ELF::R_X86_64_REX_GOTPCRELX;
213    }
214    llvm_unreachable("unexpected relocation type!");
215  }
216}
217
218enum X86_32RelType { RT32_NONE, RT32_32, RT32_16, RT32_8 };
219
220static X86_32RelType getType32(X86_64RelType T) {
221  switch (T) {
222  case RT64_NONE:
223    return RT32_NONE;
224  case RT64_64:
225    llvm_unreachable("Unimplemented");
226  case RT64_32:
227  case RT64_32S:
228    return RT32_32;
229  case RT64_16:
230    return RT32_16;
231  case RT64_8:
232    return RT32_8;
233  }
234  llvm_unreachable("unexpected relocation type!");
235}
236
237static unsigned getRelocType32(MCContext &Ctx,
238                               MCSymbolRefExpr::VariantKind Modifier,
239                               X86_32RelType Type, bool IsPCRel,
240                               MCFixupKind Kind) {
241  switch (Modifier) {
242  default:
243    llvm_unreachable("Unimplemented");
244  case MCSymbolRefExpr::VK_None:
245  case MCSymbolRefExpr::VK_X86_ABS8:
246    switch (Type) {
247    case RT32_NONE:
248      if (Modifier == MCSymbolRefExpr::VK_None)
249        return ELF::R_386_NONE;
250      llvm_unreachable("Unimplemented");
251    case RT32_32:
252      return IsPCRel ? ELF::R_386_PC32 : ELF::R_386_32;
253    case RT32_16:
254      return IsPCRel ? ELF::R_386_PC16 : ELF::R_386_16;
255    case RT32_8:
256      return IsPCRel ? ELF::R_386_PC8 : ELF::R_386_8;
257    }
258    llvm_unreachable("unexpected relocation type!");
259  case MCSymbolRefExpr::VK_GOT:
260    assert(Type == RT32_32);
261    if (IsPCRel)
262      return ELF::R_386_GOTPC;
263    // Older versions of ld.bfd/ld.gold/lld do not support R_386_GOT32X and we
264    // want to maintain compatibility.
265    if (!Ctx.getAsmInfo()->canRelaxRelocations())
266      return ELF::R_386_GOT32;
267
268    return Kind == MCFixupKind(X86::reloc_signed_4byte_relax)
269               ? ELF::R_386_GOT32X
270               : ELF::R_386_GOT32;
271  case MCSymbolRefExpr::VK_GOTOFF:
272    assert(Type == RT32_32);
273    assert(!IsPCRel);
274    return ELF::R_386_GOTOFF;
275  case MCSymbolRefExpr::VK_TLSCALL:
276    return ELF::R_386_TLS_DESC_CALL;
277  case MCSymbolRefExpr::VK_TLSDESC:
278    return ELF::R_386_TLS_GOTDESC;
279  case MCSymbolRefExpr::VK_TPOFF:
280    assert(Type == RT32_32);
281    assert(!IsPCRel);
282    return ELF::R_386_TLS_LE_32;
283  case MCSymbolRefExpr::VK_DTPOFF:
284    assert(Type == RT32_32);
285    assert(!IsPCRel);
286    return ELF::R_386_TLS_LDO_32;
287  case MCSymbolRefExpr::VK_TLSGD:
288    assert(Type == RT32_32);
289    assert(!IsPCRel);
290    return ELF::R_386_TLS_GD;
291  case MCSymbolRefExpr::VK_GOTTPOFF:
292    assert(Type == RT32_32);
293    assert(!IsPCRel);
294    return ELF::R_386_TLS_IE_32;
295  case MCSymbolRefExpr::VK_PLT:
296    assert(Type == RT32_32);
297    return ELF::R_386_PLT32;
298  case MCSymbolRefExpr::VK_INDNTPOFF:
299    assert(Type == RT32_32);
300    assert(!IsPCRel);
301    return ELF::R_386_TLS_IE;
302  case MCSymbolRefExpr::VK_NTPOFF:
303    assert(Type == RT32_32);
304    assert(!IsPCRel);
305    return ELF::R_386_TLS_LE;
306  case MCSymbolRefExpr::VK_GOTNTPOFF:
307    assert(Type == RT32_32);
308    assert(!IsPCRel);
309    return ELF::R_386_TLS_GOTIE;
310  case MCSymbolRefExpr::VK_TLSLDM:
311    assert(Type == RT32_32);
312    assert(!IsPCRel);
313    return ELF::R_386_TLS_LDM;
314  }
315}
316
317unsigned X86ELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
318                                          const MCFixup &Fixup,
319                                          bool IsPCRel) const {
320  MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
321  MCFixupKind Kind = Fixup.getKind();
322  X86_64RelType Type = getType64(Kind, Modifier, IsPCRel);
323  if (getEMachine() == ELF::EM_X86_64)
324    return getRelocType64(Ctx, Fixup.getLoc(), Modifier, Type, IsPCRel, Kind);
325
326  assert((getEMachine() == ELF::EM_386 || getEMachine() == ELF::EM_IAMCU) &&
327         "Unsupported ELF machine type.");
328  return getRelocType32(Ctx, Modifier, getType32(Type), IsPCRel, Kind);
329}
330
331std::unique_ptr<MCObjectTargetWriter>
332llvm::createX86ELFObjectWriter(bool IsELF64, uint8_t OSABI, uint16_t EMachine) {
333  return std::make_unique<X86ELFObjectWriter>(IsELF64, OSABI, EMachine);
334}
335