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
23 using namespace llvm;
24
25 namespace {
26
27 class X86ELFObjectWriter : public MCELFObjectTargetWriter {
28 public:
29 X86ELFObjectWriter(bool IsELF64, uint8_t OSABI, uint16_t EMachine);
30 ~X86ELFObjectWriter() override = default;
31
32 protected:
33 unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
34 const MCFixup &Fixup, bool IsPCRel) const override;
35 };
36
37 } // end anonymous namespace
38
X86ELFObjectWriter(bool IsELF64,uint8_t OSABI,uint16_t EMachine)39 X86ELFObjectWriter::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
47 enum X86_64RelType { RT64_NONE, RT64_64, RT64_32, RT64_32S, RT64_16, RT64_8 };
48
getType64(MCFixupKind Kind,MCSymbolRefExpr::VariantKind & Modifier,bool & IsPCRel)49 static 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
checkIs32(MCContext & Ctx,SMLoc Loc,X86_64RelType Type)91 static 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
checkIs64(MCContext & Ctx,SMLoc Loc,X86_64RelType Type)97 static void checkIs64(MCContext &Ctx, SMLoc Loc, X86_64RelType Type) {
98 if (Type != RT64_64)
99 Ctx.reportError(Loc,
100 "64 bit reloc applied to a field with a different size");
101 }
102
getRelocType64(MCContext & Ctx,SMLoc Loc,MCSymbolRefExpr::VariantKind Modifier,X86_64RelType Type,bool IsPCRel,MCFixupKind Kind)103 static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
104 MCSymbolRefExpr::VariantKind Modifier,
105 X86_64RelType Type, bool IsPCRel,
106 MCFixupKind Kind) {
107 switch (Modifier) {
108 default:
109 llvm_unreachable("Unimplemented");
110 case MCSymbolRefExpr::VK_None:
111 case MCSymbolRefExpr::VK_X86_ABS8:
112 switch (Type) {
113 case RT64_NONE:
114 if (Modifier == MCSymbolRefExpr::VK_None)
115 return ELF::R_X86_64_NONE;
116 llvm_unreachable("Unimplemented");
117 case RT64_64:
118 return IsPCRel ? ELF::R_X86_64_PC64 : ELF::R_X86_64_64;
119 case RT64_32:
120 return IsPCRel ? ELF::R_X86_64_PC32 : ELF::R_X86_64_32;
121 case RT64_32S:
122 return ELF::R_X86_64_32S;
123 case RT64_16:
124 return IsPCRel ? ELF::R_X86_64_PC16 : ELF::R_X86_64_16;
125 case RT64_8:
126 return IsPCRel ? ELF::R_X86_64_PC8 : ELF::R_X86_64_8;
127 }
128 llvm_unreachable("unexpected relocation type!");
129 case MCSymbolRefExpr::VK_GOT:
130 switch (Type) {
131 case RT64_64:
132 return IsPCRel ? ELF::R_X86_64_GOTPC64 : ELF::R_X86_64_GOT64;
133 case RT64_32:
134 return IsPCRel ? ELF::R_X86_64_GOTPC32 : ELF::R_X86_64_GOT32;
135 case RT64_32S:
136 case RT64_16:
137 case RT64_8:
138 case RT64_NONE:
139 llvm_unreachable("Unimplemented");
140 }
141 llvm_unreachable("unexpected relocation type!");
142 case MCSymbolRefExpr::VK_GOTOFF:
143 assert(!IsPCRel);
144 if (Type != RT64_64)
145 Ctx.reportError(Loc, "unsupported relocation type");
146 return ELF::R_X86_64_GOTOFF64;
147 case MCSymbolRefExpr::VK_TPOFF:
148 assert(!IsPCRel);
149 switch (Type) {
150 case RT64_64:
151 return ELF::R_X86_64_TPOFF64;
152 case RT64_32:
153 return ELF::R_X86_64_TPOFF32;
154 case RT64_32S:
155 case RT64_16:
156 case RT64_8:
157 case RT64_NONE:
158 llvm_unreachable("Unimplemented");
159 }
160 llvm_unreachable("unexpected relocation type!");
161 case MCSymbolRefExpr::VK_DTPOFF:
162 assert(!IsPCRel);
163 switch (Type) {
164 case RT64_64:
165 return ELF::R_X86_64_DTPOFF64;
166 case RT64_32:
167 return ELF::R_X86_64_DTPOFF32;
168 case RT64_32S:
169 case RT64_16:
170 case RT64_8:
171 case RT64_NONE:
172 llvm_unreachable("Unimplemented");
173 }
174 llvm_unreachable("unexpected relocation type!");
175 case MCSymbolRefExpr::VK_SIZE:
176 assert(!IsPCRel);
177 switch (Type) {
178 case RT64_64:
179 return ELF::R_X86_64_SIZE64;
180 case RT64_32:
181 return ELF::R_X86_64_SIZE32;
182 case RT64_32S:
183 case RT64_16:
184 case RT64_8:
185 case RT64_NONE:
186 llvm_unreachable("Unimplemented");
187 }
188 llvm_unreachable("unexpected relocation type!");
189 case MCSymbolRefExpr::VK_TLSCALL:
190 return ELF::R_X86_64_TLSDESC_CALL;
191 case MCSymbolRefExpr::VK_TLSDESC:
192 return ELF::R_X86_64_GOTPC32_TLSDESC;
193 case MCSymbolRefExpr::VK_TLSGD:
194 checkIs32(Ctx, Loc, Type);
195 return ELF::R_X86_64_TLSGD;
196 case MCSymbolRefExpr::VK_GOTTPOFF:
197 checkIs32(Ctx, Loc, Type);
198 return ELF::R_X86_64_GOTTPOFF;
199 case MCSymbolRefExpr::VK_TLSLD:
200 checkIs32(Ctx, Loc, Type);
201 return ELF::R_X86_64_TLSLD;
202 case MCSymbolRefExpr::VK_PLT:
203 checkIs32(Ctx, Loc, Type);
204 return ELF::R_X86_64_PLT32;
205 case MCSymbolRefExpr::VK_GOTPCREL:
206 checkIs32(Ctx, Loc, Type);
207 // Older versions of ld.bfd/ld.gold/lld
208 // do not support GOTPCRELX/REX_GOTPCRELX,
209 // and we want to keep back-compatibility.
210 if (!Ctx.getTargetOptions()->X86RelaxRelocations)
211 return ELF::R_X86_64_GOTPCREL;
212 switch (unsigned(Kind)) {
213 default:
214 return ELF::R_X86_64_GOTPCREL;
215 case X86::reloc_riprel_4byte_relax:
216 return ELF::R_X86_64_GOTPCRELX;
217 case X86::reloc_riprel_4byte_relax_rex:
218 case X86::reloc_riprel_4byte_movq_load:
219 return ELF::R_X86_64_REX_GOTPCRELX;
220 }
221 llvm_unreachable("unexpected relocation type!");
222 case MCSymbolRefExpr::VK_GOTPCREL_NORELAX:
223 checkIs32(Ctx, Loc, Type);
224 return ELF::R_X86_64_GOTPCREL;
225 case MCSymbolRefExpr::VK_X86_PLTOFF:
226 checkIs64(Ctx, Loc, Type);
227 return ELF::R_X86_64_PLTOFF64;
228 }
229 }
230
231 enum X86_32RelType { RT32_NONE, RT32_32, RT32_16, RT32_8 };
232
getRelocType32(MCContext & Ctx,SMLoc Loc,MCSymbolRefExpr::VariantKind Modifier,X86_32RelType Type,bool IsPCRel,MCFixupKind Kind)233 static unsigned getRelocType32(MCContext &Ctx, SMLoc Loc,
234 MCSymbolRefExpr::VariantKind Modifier,
235 X86_32RelType Type, bool IsPCRel,
236 MCFixupKind Kind) {
237 switch (Modifier) {
238 default:
239 llvm_unreachable("Unimplemented");
240 case MCSymbolRefExpr::VK_None:
241 case MCSymbolRefExpr::VK_X86_ABS8:
242 switch (Type) {
243 case RT32_NONE:
244 if (Modifier == MCSymbolRefExpr::VK_None)
245 return ELF::R_386_NONE;
246 llvm_unreachable("Unimplemented");
247 case RT32_32:
248 return IsPCRel ? ELF::R_386_PC32 : ELF::R_386_32;
249 case RT32_16:
250 return IsPCRel ? ELF::R_386_PC16 : ELF::R_386_16;
251 case RT32_8:
252 return IsPCRel ? ELF::R_386_PC8 : ELF::R_386_8;
253 }
254 llvm_unreachable("unexpected relocation type!");
255 case MCSymbolRefExpr::VK_GOT:
256 if (Type != RT32_32)
257 break;
258 if (IsPCRel)
259 return ELF::R_386_GOTPC;
260 // Older versions of ld.bfd/ld.gold/lld do not support R_386_GOT32X and we
261 // want to maintain compatibility.
262 if (!Ctx.getTargetOptions()->X86RelaxRelocations)
263 return ELF::R_386_GOT32;
264
265 return Kind == MCFixupKind(X86::reloc_signed_4byte_relax)
266 ? ELF::R_386_GOT32X
267 : ELF::R_386_GOT32;
268 case MCSymbolRefExpr::VK_GOTOFF:
269 assert(!IsPCRel);
270 if (Type != RT32_32)
271 break;
272 return ELF::R_386_GOTOFF;
273 case MCSymbolRefExpr::VK_TLSCALL:
274 return ELF::R_386_TLS_DESC_CALL;
275 case MCSymbolRefExpr::VK_TLSDESC:
276 return ELF::R_386_TLS_GOTDESC;
277 case MCSymbolRefExpr::VK_TPOFF:
278 if (Type != RT32_32)
279 break;
280 assert(!IsPCRel);
281 return ELF::R_386_TLS_LE_32;
282 case MCSymbolRefExpr::VK_DTPOFF:
283 if (Type != RT32_32)
284 break;
285 assert(!IsPCRel);
286 return ELF::R_386_TLS_LDO_32;
287 case MCSymbolRefExpr::VK_TLSGD:
288 if (Type != RT32_32)
289 break;
290 assert(!IsPCRel);
291 return ELF::R_386_TLS_GD;
292 case MCSymbolRefExpr::VK_GOTTPOFF:
293 if (Type != RT32_32)
294 break;
295 assert(!IsPCRel);
296 return ELF::R_386_TLS_IE_32;
297 case MCSymbolRefExpr::VK_PLT:
298 if (Type != RT32_32)
299 break;
300 return ELF::R_386_PLT32;
301 case MCSymbolRefExpr::VK_INDNTPOFF:
302 if (Type != RT32_32)
303 break;
304 assert(!IsPCRel);
305 return ELF::R_386_TLS_IE;
306 case MCSymbolRefExpr::VK_NTPOFF:
307 if (Type != RT32_32)
308 break;
309 assert(!IsPCRel);
310 return ELF::R_386_TLS_LE;
311 case MCSymbolRefExpr::VK_GOTNTPOFF:
312 if (Type != RT32_32)
313 break;
314 assert(!IsPCRel);
315 return ELF::R_386_TLS_GOTIE;
316 case MCSymbolRefExpr::VK_TLSLDM:
317 if (Type != RT32_32)
318 break;
319 assert(!IsPCRel);
320 return ELF::R_386_TLS_LDM;
321 }
322 Ctx.reportError(Loc, "unsupported relocation type");
323 return ELF::R_386_NONE;
324 }
325
getRelocType(MCContext & Ctx,const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const326 unsigned X86ELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
327 const MCFixup &Fixup,
328 bool IsPCRel) const {
329 MCFixupKind Kind = Fixup.getKind();
330 if (Kind >= FirstLiteralRelocationKind)
331 return Kind - FirstLiteralRelocationKind;
332 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
333 X86_64RelType Type = getType64(Kind, Modifier, IsPCRel);
334 if (getEMachine() == ELF::EM_X86_64)
335 return getRelocType64(Ctx, Fixup.getLoc(), Modifier, Type, IsPCRel, Kind);
336
337 assert((getEMachine() == ELF::EM_386 || getEMachine() == ELF::EM_IAMCU) &&
338 "Unsupported ELF machine type.");
339
340 X86_32RelType RelType = RT32_NONE;
341 switch (Type) {
342 case RT64_NONE:
343 break;
344 case RT64_64:
345 Ctx.reportError(Fixup.getLoc(), "unsupported relocation type");
346 return ELF::R_386_NONE;
347 case RT64_32:
348 case RT64_32S:
349 RelType = RT32_32;
350 break;
351 case RT64_16:
352 RelType = RT32_16;
353 break;
354 case RT64_8:
355 RelType = RT32_8;
356 break;
357 }
358 return getRelocType32(Ctx, Fixup.getLoc(), Modifier, RelType, IsPCRel, Kind);
359 }
360
361 std::unique_ptr<MCObjectTargetWriter>
createX86ELFObjectWriter(bool IsELF64,uint8_t OSABI,uint16_t EMachine)362 llvm::createX86ELFObjectWriter(bool IsELF64, uint8_t OSABI, uint16_t EMachine) {
363 return std::make_unique<X86ELFObjectWriter>(IsELF64, OSABI, EMachine);
364 }
365