1 //===-- X86MachObjectWriter.cpp - X86 Mach-O Writer -----------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "MCTargetDesc/X86FixupKinds.h" 11 #include "MCTargetDesc/X86MCTargetDesc.h" 12 #include "llvm/MC/MCAssembler.h" 13 #include "llvm/MC/MCAsmLayout.h" 14 #include "llvm/MC/MCMachObjectWriter.h" 15 #include "llvm/MC/MCSectionMachO.h" 16 #include "llvm/MC/MCValue.h" 17 #include "llvm/ADT/Twine.h" 18 #include "llvm/Support/ErrorHandling.h" 19 #include "llvm/Object/MachOFormat.h" 20 21 using namespace llvm; 22 using namespace llvm::object; 23 24 namespace { 25 class X86MachObjectWriter : public MCMachObjectTargetWriter { 26 void RecordScatteredRelocation(MachObjectWriter *Writer, 27 const MCAssembler &Asm, 28 const MCAsmLayout &Layout, 29 const MCFragment *Fragment, 30 const MCFixup &Fixup, 31 MCValue Target, 32 unsigned Log2Size, 33 uint64_t &FixedValue); 34 void RecordTLVPRelocation(MachObjectWriter *Writer, 35 const MCAssembler &Asm, 36 const MCAsmLayout &Layout, 37 const MCFragment *Fragment, 38 const MCFixup &Fixup, 39 MCValue Target, 40 uint64_t &FixedValue); 41 42 void RecordX86Relocation(MachObjectWriter *Writer, 43 const MCAssembler &Asm, 44 const MCAsmLayout &Layout, 45 const MCFragment *Fragment, 46 const MCFixup &Fixup, 47 MCValue Target, 48 uint64_t &FixedValue); 49 void RecordX86_64Relocation(MachObjectWriter *Writer, 50 const MCAssembler &Asm, 51 const MCAsmLayout &Layout, 52 const MCFragment *Fragment, 53 const MCFixup &Fixup, 54 MCValue Target, 55 uint64_t &FixedValue); 56 public: 57 X86MachObjectWriter(bool Is64Bit, uint32_t CPUType, 58 uint32_t CPUSubtype) 59 : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype, 60 /*UseAggressiveSymbolFolding=*/Is64Bit) {} 61 62 void RecordRelocation(MachObjectWriter *Writer, 63 const MCAssembler &Asm, const MCAsmLayout &Layout, 64 const MCFragment *Fragment, const MCFixup &Fixup, 65 MCValue Target, uint64_t &FixedValue) { 66 if (Writer->is64Bit()) 67 RecordX86_64Relocation(Writer, Asm, Layout, Fragment, Fixup, Target, 68 FixedValue); 69 else 70 RecordX86Relocation(Writer, Asm, Layout, Fragment, Fixup, Target, 71 FixedValue); 72 } 73 }; 74 } 75 76 static bool isFixupKindRIPRel(unsigned Kind) { 77 return Kind == X86::reloc_riprel_4byte || 78 Kind == X86::reloc_riprel_4byte_movq_load; 79 } 80 81 static unsigned getFixupKindLog2Size(unsigned Kind) { 82 switch (Kind) { 83 default: 84 llvm_unreachable("invalid fixup kind!"); 85 case FK_PCRel_1: 86 case FK_Data_1: return 0; 87 case FK_PCRel_2: 88 case FK_Data_2: return 1; 89 case FK_PCRel_4: 90 // FIXME: Remove these!!! 91 case X86::reloc_riprel_4byte: 92 case X86::reloc_riprel_4byte_movq_load: 93 case X86::reloc_signed_4byte: 94 case FK_Data_4: return 2; 95 case FK_Data_8: return 3; 96 } 97 } 98 99 void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer, 100 const MCAssembler &Asm, 101 const MCAsmLayout &Layout, 102 const MCFragment *Fragment, 103 const MCFixup &Fixup, 104 MCValue Target, 105 uint64_t &FixedValue) { 106 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind()); 107 unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind()); 108 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind()); 109 110 // See <reloc.h>. 111 uint32_t FixupOffset = 112 Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 113 uint32_t FixupAddress = 114 Writer->getFragmentAddress(Fragment, Layout) + Fixup.getOffset(); 115 int64_t Value = 0; 116 unsigned Index = 0; 117 unsigned IsExtern = 0; 118 unsigned Type = 0; 119 120 Value = Target.getConstant(); 121 122 if (IsPCRel) { 123 // Compensate for the relocation offset, Darwin x86_64 relocations only have 124 // the addend and appear to have attempted to define it to be the actual 125 // expression addend without the PCrel bias. However, instructions with data 126 // following the relocation are not accommodated for (see comment below 127 // regarding SIGNED{1,2,4}), so it isn't exactly that either. 128 Value += 1LL << Log2Size; 129 } 130 131 if (Target.isAbsolute()) { // constant 132 // SymbolNum of 0 indicates the absolute section. 133 Type = macho::RIT_X86_64_Unsigned; 134 Index = 0; 135 136 // FIXME: I believe this is broken, I don't think the linker can understand 137 // it. I think it would require a local relocation, but I'm not sure if that 138 // would work either. The official way to get an absolute PCrel relocation 139 // is to use an absolute symbol (which we don't support yet). 140 if (IsPCRel) { 141 IsExtern = 1; 142 Type = macho::RIT_X86_64_Branch; 143 } 144 } else if (Target.getSymB()) { // A - B + constant 145 const MCSymbol *A = &Target.getSymA()->getSymbol(); 146 MCSymbolData &A_SD = Asm.getSymbolData(*A); 147 const MCSymbolData *A_Base = Asm.getAtom(&A_SD); 148 149 const MCSymbol *B = &Target.getSymB()->getSymbol(); 150 MCSymbolData &B_SD = Asm.getSymbolData(*B); 151 const MCSymbolData *B_Base = Asm.getAtom(&B_SD); 152 153 // Neither symbol can be modified. 154 if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None || 155 Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None) 156 report_fatal_error("unsupported relocation of modified symbol"); 157 158 // We don't support PCrel relocations of differences. Darwin 'as' doesn't 159 // implement most of these correctly. 160 if (IsPCRel) 161 report_fatal_error("unsupported pc-relative relocation of difference"); 162 163 // The support for the situation where one or both of the symbols would 164 // require a local relocation is handled just like if the symbols were 165 // external. This is certainly used in the case of debug sections where the 166 // section has only temporary symbols and thus the symbols don't have base 167 // symbols. This is encoded using the section ordinal and non-extern 168 // relocation entries. 169 170 // Darwin 'as' doesn't emit correct relocations for this (it ends up with a 171 // single SIGNED relocation); reject it for now. Except the case where both 172 // symbols don't have a base, equal but both NULL. 173 if (A_Base == B_Base && A_Base) 174 report_fatal_error("unsupported relocation with identical base"); 175 176 Value += Writer->getSymbolAddress(&A_SD, Layout) - 177 (A_Base == NULL ? 0 : Writer->getSymbolAddress(A_Base, Layout)); 178 Value -= Writer->getSymbolAddress(&B_SD, Layout) - 179 (B_Base == NULL ? 0 : Writer->getSymbolAddress(B_Base, Layout)); 180 181 if (A_Base) { 182 Index = A_Base->getIndex(); 183 IsExtern = 1; 184 } 185 else { 186 Index = A_SD.getFragment()->getParent()->getOrdinal() + 1; 187 IsExtern = 0; 188 } 189 Type = macho::RIT_X86_64_Unsigned; 190 191 macho::RelocationEntry MRE; 192 MRE.Word0 = FixupOffset; 193 MRE.Word1 = ((Index << 0) | 194 (IsPCRel << 24) | 195 (Log2Size << 25) | 196 (IsExtern << 27) | 197 (Type << 28)); 198 Writer->addRelocation(Fragment->getParent(), MRE); 199 200 if (B_Base) { 201 Index = B_Base->getIndex(); 202 IsExtern = 1; 203 } 204 else { 205 Index = B_SD.getFragment()->getParent()->getOrdinal() + 1; 206 IsExtern = 0; 207 } 208 Type = macho::RIT_X86_64_Subtractor; 209 } else { 210 const MCSymbol *Symbol = &Target.getSymA()->getSymbol(); 211 MCSymbolData &SD = Asm.getSymbolData(*Symbol); 212 const MCSymbolData *Base = Asm.getAtom(&SD); 213 214 // Relocations inside debug sections always use local relocations when 215 // possible. This seems to be done because the debugger doesn't fully 216 // understand x86_64 relocation entries, and expects to find values that 217 // have already been fixed up. 218 if (Symbol->isInSection()) { 219 const MCSectionMachO &Section = static_cast<const MCSectionMachO&>( 220 Fragment->getParent()->getSection()); 221 if (Section.hasAttribute(MCSectionMachO::S_ATTR_DEBUG)) 222 Base = 0; 223 } 224 225 // x86_64 almost always uses external relocations, except when there is no 226 // symbol to use as a base address (a local symbol with no preceding 227 // non-local symbol). 228 if (Base) { 229 Index = Base->getIndex(); 230 IsExtern = 1; 231 232 // Add the local offset, if needed. 233 if (Base != &SD) 234 Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base); 235 } else if (Symbol->isInSection() && !Symbol->isVariable()) { 236 // The index is the section ordinal (1-based). 237 Index = SD.getFragment()->getParent()->getOrdinal() + 1; 238 IsExtern = 0; 239 Value += Writer->getSymbolAddress(&SD, Layout); 240 241 if (IsPCRel) 242 Value -= FixupAddress + (1 << Log2Size); 243 } else if (Symbol->isVariable()) { 244 const MCExpr *Value = Symbol->getVariableValue(); 245 int64_t Res; 246 bool isAbs = Value->EvaluateAsAbsolute(Res, Layout, 247 Writer->getSectionAddressMap()); 248 if (isAbs) { 249 FixedValue = Res; 250 return; 251 } else { 252 report_fatal_error("unsupported relocation of variable '" + 253 Symbol->getName() + "'"); 254 } 255 } else { 256 report_fatal_error("unsupported relocation of undefined symbol '" + 257 Symbol->getName() + "'"); 258 } 259 260 MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind(); 261 if (IsPCRel) { 262 if (IsRIPRel) { 263 if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) { 264 // x86_64 distinguishes movq foo@GOTPCREL so that the linker can 265 // rewrite the movq to an leaq at link time if the symbol ends up in 266 // the same linkage unit. 267 if (unsigned(Fixup.getKind()) == X86::reloc_riprel_4byte_movq_load) 268 Type = macho::RIT_X86_64_GOTLoad; 269 else 270 Type = macho::RIT_X86_64_GOT; 271 } else if (Modifier == MCSymbolRefExpr::VK_TLVP) { 272 Type = macho::RIT_X86_64_TLV; 273 } else if (Modifier != MCSymbolRefExpr::VK_None) { 274 report_fatal_error("unsupported symbol modifier in relocation"); 275 } else { 276 Type = macho::RIT_X86_64_Signed; 277 278 // The Darwin x86_64 relocation format has a problem where it cannot 279 // encode an address (L<foo> + <constant>) which is outside the atom 280 // containing L<foo>. Generally, this shouldn't occur but it does 281 // happen when we have a RIPrel instruction with data following the 282 // relocation entry (e.g., movb $012, L0(%rip)). Even with the PCrel 283 // adjustment Darwin x86_64 uses, the offset is still negative and the 284 // linker has no way to recognize this. 285 // 286 // To work around this, Darwin uses several special relocation types 287 // to indicate the offsets. However, the specification or 288 // implementation of these seems to also be incomplete; they should 289 // adjust the addend as well based on the actual encoded instruction 290 // (the additional bias), but instead appear to just look at the final 291 // offset. 292 switch (-(Target.getConstant() + (1LL << Log2Size))) { 293 case 1: Type = macho::RIT_X86_64_Signed1; break; 294 case 2: Type = macho::RIT_X86_64_Signed2; break; 295 case 4: Type = macho::RIT_X86_64_Signed4; break; 296 } 297 } 298 } else { 299 if (Modifier != MCSymbolRefExpr::VK_None) 300 report_fatal_error("unsupported symbol modifier in branch " 301 "relocation"); 302 303 Type = macho::RIT_X86_64_Branch; 304 } 305 } else { 306 if (Modifier == MCSymbolRefExpr::VK_GOT) { 307 Type = macho::RIT_X86_64_GOT; 308 } else if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) { 309 // GOTPCREL is allowed as a modifier on non-PCrel instructions, in which 310 // case all we do is set the PCrel bit in the relocation entry; this is 311 // used with exception handling, for example. The source is required to 312 // include any necessary offset directly. 313 Type = macho::RIT_X86_64_GOT; 314 IsPCRel = 1; 315 } else if (Modifier == MCSymbolRefExpr::VK_TLVP) { 316 report_fatal_error("TLVP symbol modifier should have been rip-rel"); 317 } else if (Modifier != MCSymbolRefExpr::VK_None) 318 report_fatal_error("unsupported symbol modifier in relocation"); 319 else 320 Type = macho::RIT_X86_64_Unsigned; 321 } 322 } 323 324 // x86_64 always writes custom values into the fixups. 325 FixedValue = Value; 326 327 // struct relocation_info (8 bytes) 328 macho::RelocationEntry MRE; 329 MRE.Word0 = FixupOffset; 330 MRE.Word1 = ((Index << 0) | 331 (IsPCRel << 24) | 332 (Log2Size << 25) | 333 (IsExtern << 27) | 334 (Type << 28)); 335 Writer->addRelocation(Fragment->getParent(), MRE); 336 } 337 338 void X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer, 339 const MCAssembler &Asm, 340 const MCAsmLayout &Layout, 341 const MCFragment *Fragment, 342 const MCFixup &Fixup, 343 MCValue Target, 344 unsigned Log2Size, 345 uint64_t &FixedValue) { 346 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset(); 347 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind()); 348 unsigned Type = macho::RIT_Vanilla; 349 350 // See <reloc.h>. 351 const MCSymbol *A = &Target.getSymA()->getSymbol(); 352 MCSymbolData *A_SD = &Asm.getSymbolData(*A); 353 354 if (!A_SD->getFragment()) 355 report_fatal_error("symbol '" + A->getName() + 356 "' can not be undefined in a subtraction expression"); 357 358 uint32_t Value = Writer->getSymbolAddress(A_SD, Layout); 359 uint64_t SecAddr = Writer->getSectionAddress(A_SD->getFragment()->getParent()); 360 FixedValue += SecAddr; 361 uint32_t Value2 = 0; 362 363 if (const MCSymbolRefExpr *B = Target.getSymB()) { 364 MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol()); 365 366 if (!B_SD->getFragment()) 367 report_fatal_error("symbol '" + B->getSymbol().getName() + 368 "' can not be undefined in a subtraction expression"); 369 370 // Select the appropriate difference relocation type. 371 // 372 // Note that there is no longer any semantic difference between these two 373 // relocation types from the linkers point of view, this is done solely for 374 // pedantic compatibility with 'as'. 375 Type = A_SD->isExternal() ? (unsigned)macho::RIT_Difference : 376 (unsigned)macho::RIT_Generic_LocalDifference; 377 Value2 = Writer->getSymbolAddress(B_SD, Layout); 378 FixedValue -= Writer->getSectionAddress(B_SD->getFragment()->getParent()); 379 } 380 381 // Relocations are written out in reverse order, so the PAIR comes first. 382 if (Type == macho::RIT_Difference || 383 Type == macho::RIT_Generic_LocalDifference) { 384 macho::RelocationEntry MRE; 385 MRE.Word0 = ((0 << 0) | 386 (macho::RIT_Pair << 24) | 387 (Log2Size << 28) | 388 (IsPCRel << 30) | 389 macho::RF_Scattered); 390 MRE.Word1 = Value2; 391 Writer->addRelocation(Fragment->getParent(), MRE); 392 } 393 394 macho::RelocationEntry MRE; 395 MRE.Word0 = ((FixupOffset << 0) | 396 (Type << 24) | 397 (Log2Size << 28) | 398 (IsPCRel << 30) | 399 macho::RF_Scattered); 400 MRE.Word1 = Value; 401 Writer->addRelocation(Fragment->getParent(), MRE); 402 } 403 404 void X86MachObjectWriter::RecordTLVPRelocation(MachObjectWriter *Writer, 405 const MCAssembler &Asm, 406 const MCAsmLayout &Layout, 407 const MCFragment *Fragment, 408 const MCFixup &Fixup, 409 MCValue Target, 410 uint64_t &FixedValue) { 411 assert(Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP && 412 !is64Bit() && 413 "Should only be called with a 32-bit TLVP relocation!"); 414 415 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind()); 416 uint32_t Value = Layout.getFragmentOffset(Fragment)+Fixup.getOffset(); 417 unsigned IsPCRel = 0; 418 419 // Get the symbol data. 420 MCSymbolData *SD_A = &Asm.getSymbolData(Target.getSymA()->getSymbol()); 421 unsigned Index = SD_A->getIndex(); 422 423 // We're only going to have a second symbol in pic mode and it'll be a 424 // subtraction from the picbase. For 32-bit pic the addend is the difference 425 // between the picbase and the next address. For 32-bit static the addend is 426 // zero. 427 if (Target.getSymB()) { 428 // If this is a subtraction then we're pcrel. 429 uint32_t FixupAddress = 430 Writer->getFragmentAddress(Fragment, Layout) + Fixup.getOffset(); 431 MCSymbolData *SD_B = &Asm.getSymbolData(Target.getSymB()->getSymbol()); 432 IsPCRel = 1; 433 FixedValue = (FixupAddress - Writer->getSymbolAddress(SD_B, Layout) + 434 Target.getConstant()); 435 FixedValue += 1ULL << Log2Size; 436 } else { 437 FixedValue = 0; 438 } 439 440 // struct relocation_info (8 bytes) 441 macho::RelocationEntry MRE; 442 MRE.Word0 = Value; 443 MRE.Word1 = ((Index << 0) | 444 (IsPCRel << 24) | 445 (Log2Size << 25) | 446 (1 << 27) | // Extern 447 (macho::RIT_Generic_TLV << 28)); // Type 448 Writer->addRelocation(Fragment->getParent(), MRE); 449 } 450 451 void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer, 452 const MCAssembler &Asm, 453 const MCAsmLayout &Layout, 454 const MCFragment *Fragment, 455 const MCFixup &Fixup, 456 MCValue Target, 457 uint64_t &FixedValue) { 458 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind()); 459 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind()); 460 461 // If this is a 32-bit TLVP reloc it's handled a bit differently. 462 if (Target.getSymA() && 463 Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP) { 464 RecordTLVPRelocation(Writer, Asm, Layout, Fragment, Fixup, Target, 465 FixedValue); 466 return; 467 } 468 469 // If this is a difference or a defined symbol plus an offset, then we need a 470 // scattered relocation entry. Differences always require scattered 471 // relocations. 472 if (Target.getSymB()) 473 return RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup, 474 Target, Log2Size, FixedValue); 475 476 // Get the symbol data, if any. 477 MCSymbolData *SD = 0; 478 if (Target.getSymA()) 479 SD = &Asm.getSymbolData(Target.getSymA()->getSymbol()); 480 481 // If this is an internal relocation with an offset, it also needs a scattered 482 // relocation entry. 483 uint32_t Offset = Target.getConstant(); 484 if (IsPCRel) 485 Offset += 1 << Log2Size; 486 if (Offset && SD && !Writer->doesSymbolRequireExternRelocation(SD)) 487 return RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup, 488 Target, Log2Size, FixedValue); 489 490 // See <reloc.h>. 491 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset(); 492 unsigned Index = 0; 493 unsigned IsExtern = 0; 494 unsigned Type = 0; 495 496 if (Target.isAbsolute()) { // constant 497 // SymbolNum of 0 indicates the absolute section. 498 // 499 // FIXME: Currently, these are never generated (see code below). I cannot 500 // find a case where they are actually emitted. 501 Type = macho::RIT_Vanilla; 502 } else { 503 // Resolve constant variables. 504 if (SD->getSymbol().isVariable()) { 505 int64_t Res; 506 if (SD->getSymbol().getVariableValue()->EvaluateAsAbsolute( 507 Res, Layout, Writer->getSectionAddressMap())) { 508 FixedValue = Res; 509 return; 510 } 511 } 512 513 // Check whether we need an external or internal relocation. 514 if (Writer->doesSymbolRequireExternRelocation(SD)) { 515 IsExtern = 1; 516 Index = SD->getIndex(); 517 // For external relocations, make sure to offset the fixup value to 518 // compensate for the addend of the symbol address, if it was 519 // undefined. This occurs with weak definitions, for example. 520 if (!SD->Symbol->isUndefined()) 521 FixedValue -= Layout.getSymbolOffset(SD); 522 } else { 523 // The index is the section ordinal (1-based). 524 const MCSectionData &SymSD = Asm.getSectionData( 525 SD->getSymbol().getSection()); 526 Index = SymSD.getOrdinal() + 1; 527 FixedValue += Writer->getSectionAddress(&SymSD); 528 } 529 if (IsPCRel) 530 FixedValue -= Writer->getSectionAddress(Fragment->getParent()); 531 532 Type = macho::RIT_Vanilla; 533 } 534 535 // struct relocation_info (8 bytes) 536 macho::RelocationEntry MRE; 537 MRE.Word0 = FixupOffset; 538 MRE.Word1 = ((Index << 0) | 539 (IsPCRel << 24) | 540 (Log2Size << 25) | 541 (IsExtern << 27) | 542 (Type << 28)); 543 Writer->addRelocation(Fragment->getParent(), MRE); 544 } 545 546 MCObjectWriter *llvm::createX86MachObjectWriter(raw_ostream &OS, 547 bool Is64Bit, 548 uint32_t CPUType, 549 uint32_t CPUSubtype) { 550 return createMachObjectWriter(new X86MachObjectWriter(Is64Bit, 551 CPUType, 552 CPUSubtype), 553 OS, /*IsLittleEndian=*/true); 554 } 555
