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(Type == RT64_64);
144 assert(!IsPCRel);
145 return ELF::R_X86_64_GOTOFF64;
146 case MCSymbolRefExpr::VK_TPOFF:
147 assert(!IsPCRel);
148 switch (Type) {
149 case RT64_64:
150 return ELF::R_X86_64_TPOFF64;
151 case RT64_32:
152 return ELF::R_X86_64_TPOFF32;
153 case RT64_32S:
154 case RT64_16:
155 case RT64_8:
156 case RT64_NONE:
157 llvm_unreachable("Unimplemented");
158 }
159 llvm_unreachable("unexpected relocation type!");
160 case MCSymbolRefExpr::VK_DTPOFF:
161 assert(!IsPCRel);
162 switch (Type) {
163 case RT64_64:
164 return ELF::R_X86_64_DTPOFF64;
165 case RT64_32:
166 return ELF::R_X86_64_DTPOFF32;
167 case RT64_32S:
168 case RT64_16:
169 case RT64_8:
170 case RT64_NONE:
171 llvm_unreachable("Unimplemented");
172 }
173 llvm_unreachable("unexpected relocation type!");
174 case MCSymbolRefExpr::VK_SIZE:
175 assert(!IsPCRel);
176 switch (Type) {
177 case RT64_64:
178 return ELF::R_X86_64_SIZE64;
179 case RT64_32:
180 return ELF::R_X86_64_SIZE32;
181 case RT64_32S:
182 case RT64_16:
183 case RT64_8:
184 case RT64_NONE:
185 llvm_unreachable("Unimplemented");
186 }
187 llvm_unreachable("unexpected relocation type!");
188 case MCSymbolRefExpr::VK_TLSCALL:
189 return ELF::R_X86_64_TLSDESC_CALL;
190 case MCSymbolRefExpr::VK_TLSDESC:
191 return ELF::R_X86_64_GOTPC32_TLSDESC;
192 case MCSymbolRefExpr::VK_TLSGD:
193 checkIs32(Ctx, Loc, Type);
194 return ELF::R_X86_64_TLSGD;
195 case MCSymbolRefExpr::VK_GOTTPOFF:
196 checkIs32(Ctx, Loc, Type);
197 return ELF::R_X86_64_GOTTPOFF;
198 case MCSymbolRefExpr::VK_TLSLD:
199 checkIs32(Ctx, Loc, Type);
200 return ELF::R_X86_64_TLSLD;
201 case MCSymbolRefExpr::VK_PLT:
202 checkIs32(Ctx, Loc, Type);
203 return ELF::R_X86_64_PLT32;
204 case MCSymbolRefExpr::VK_GOTPCREL:
205 checkIs32(Ctx, Loc, Type);
206 // Older versions of ld.bfd/ld.gold/lld
207 // do not support GOTPCRELX/REX_GOTPCRELX,
208 // and we want to keep back-compatibility.
209 if (!Ctx.getAsmInfo()->canRelaxRelocations())
210 return ELF::R_X86_64_GOTPCREL;
211 switch (unsigned(Kind)) {
212 default:
213 return ELF::R_X86_64_GOTPCREL;
214 case X86::reloc_riprel_4byte_relax:
215 return ELF::R_X86_64_GOTPCRELX;
216 case X86::reloc_riprel_4byte_relax_rex:
217 case X86::reloc_riprel_4byte_movq_load:
218 return ELF::R_X86_64_REX_GOTPCRELX;
219 }
220 llvm_unreachable("unexpected relocation type!");
221 case MCSymbolRefExpr::VK_X86_PLTOFF:
222 checkIs64(Ctx, Loc, Type);
223 return ELF::R_X86_64_PLTOFF64;
224 }
225 }
226
227 enum X86_32RelType { RT32_NONE, RT32_32, RT32_16, RT32_8 };
228
getType32(X86_64RelType T)229 static X86_32RelType getType32(X86_64RelType T) {
230 switch (T) {
231 case RT64_NONE:
232 return RT32_NONE;
233 case RT64_64:
234 llvm_unreachable("Unimplemented");
235 case RT64_32:
236 case RT64_32S:
237 return RT32_32;
238 case RT64_16:
239 return RT32_16;
240 case RT64_8:
241 return RT32_8;
242 }
243 llvm_unreachable("unexpected relocation type!");
244 }
245
getRelocType32(MCContext & Ctx,MCSymbolRefExpr::VariantKind Modifier,X86_32RelType Type,bool IsPCRel,MCFixupKind Kind)246 static unsigned getRelocType32(MCContext &Ctx,
247 MCSymbolRefExpr::VariantKind Modifier,
248 X86_32RelType Type, bool IsPCRel,
249 MCFixupKind Kind) {
250 switch (Modifier) {
251 default:
252 llvm_unreachable("Unimplemented");
253 case MCSymbolRefExpr::VK_None:
254 case MCSymbolRefExpr::VK_X86_ABS8:
255 switch (Type) {
256 case RT32_NONE:
257 if (Modifier == MCSymbolRefExpr::VK_None)
258 return ELF::R_386_NONE;
259 llvm_unreachable("Unimplemented");
260 case RT32_32:
261 return IsPCRel ? ELF::R_386_PC32 : ELF::R_386_32;
262 case RT32_16:
263 return IsPCRel ? ELF::R_386_PC16 : ELF::R_386_16;
264 case RT32_8:
265 return IsPCRel ? ELF::R_386_PC8 : ELF::R_386_8;
266 }
267 llvm_unreachable("unexpected relocation type!");
268 case MCSymbolRefExpr::VK_GOT:
269 assert(Type == RT32_32);
270 if (IsPCRel)
271 return ELF::R_386_GOTPC;
272 // Older versions of ld.bfd/ld.gold/lld do not support R_386_GOT32X and we
273 // want to maintain compatibility.
274 if (!Ctx.getAsmInfo()->canRelaxRelocations())
275 return ELF::R_386_GOT32;
276
277 return Kind == MCFixupKind(X86::reloc_signed_4byte_relax)
278 ? ELF::R_386_GOT32X
279 : ELF::R_386_GOT32;
280 case MCSymbolRefExpr::VK_GOTOFF:
281 assert(Type == RT32_32);
282 assert(!IsPCRel);
283 return ELF::R_386_GOTOFF;
284 case MCSymbolRefExpr::VK_TLSCALL:
285 return ELF::R_386_TLS_DESC_CALL;
286 case MCSymbolRefExpr::VK_TLSDESC:
287 return ELF::R_386_TLS_GOTDESC;
288 case MCSymbolRefExpr::VK_TPOFF:
289 assert(Type == RT32_32);
290 assert(!IsPCRel);
291 return ELF::R_386_TLS_LE_32;
292 case MCSymbolRefExpr::VK_DTPOFF:
293 assert(Type == RT32_32);
294 assert(!IsPCRel);
295 return ELF::R_386_TLS_LDO_32;
296 case MCSymbolRefExpr::VK_TLSGD:
297 assert(Type == RT32_32);
298 assert(!IsPCRel);
299 return ELF::R_386_TLS_GD;
300 case MCSymbolRefExpr::VK_GOTTPOFF:
301 assert(Type == RT32_32);
302 assert(!IsPCRel);
303 return ELF::R_386_TLS_IE_32;
304 case MCSymbolRefExpr::VK_PLT:
305 assert(Type == RT32_32);
306 return ELF::R_386_PLT32;
307 case MCSymbolRefExpr::VK_INDNTPOFF:
308 assert(Type == RT32_32);
309 assert(!IsPCRel);
310 return ELF::R_386_TLS_IE;
311 case MCSymbolRefExpr::VK_NTPOFF:
312 assert(Type == RT32_32);
313 assert(!IsPCRel);
314 return ELF::R_386_TLS_LE;
315 case MCSymbolRefExpr::VK_GOTNTPOFF:
316 assert(Type == RT32_32);
317 assert(!IsPCRel);
318 return ELF::R_386_TLS_GOTIE;
319 case MCSymbolRefExpr::VK_TLSLDM:
320 assert(Type == RT32_32);
321 assert(!IsPCRel);
322 return ELF::R_386_TLS_LDM;
323 }
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 return getRelocType32(Ctx, Modifier, getType32(Type), IsPCRel, Kind);
340 }
341
342 std::unique_ptr<MCObjectTargetWriter>
createX86ELFObjectWriter(bool IsELF64,uint8_t OSABI,uint16_t EMachine)343 llvm::createX86ELFObjectWriter(bool IsELF64, uint8_t OSABI, uint16_t EMachine) {
344 return std::make_unique<X86ELFObjectWriter>(IsELF64, OSABI, EMachine);
345 }
346