MCAssembler.cpp revision 205407
1//===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===// 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#define DEBUG_TYPE "assembler" 11#include "llvm/MC/MCAssembler.h" 12#include "llvm/MC/MCAsmLayout.h" 13#include "llvm/MC/MCCodeEmitter.h" 14#include "llvm/MC/MCExpr.h" 15#include "llvm/MC/MCObjectWriter.h" 16#include "llvm/MC/MCSymbol.h" 17#include "llvm/MC/MCValue.h" 18#include "llvm/ADT/OwningPtr.h" 19#include "llvm/ADT/Statistic.h" 20#include "llvm/ADT/StringExtras.h" 21#include "llvm/ADT/Twine.h" 22#include "llvm/Support/ErrorHandling.h" 23#include "llvm/Support/raw_ostream.h" 24#include "llvm/Support/Debug.h" 25#include "llvm/Target/TargetRegistry.h" 26#include "llvm/Target/TargetAsmBackend.h" 27 28// FIXME: Gross. 29#include "../Target/X86/X86FixupKinds.h" 30 31#include <vector> 32using namespace llvm; 33 34STATISTIC(EmittedFragments, "Number of emitted assembler fragments"); 35 36// FIXME FIXME FIXME: There are number of places in this file where we convert 37// what is a 64-bit assembler value used for computation into a value in the 38// object file, which may truncate it. We should detect that truncation where 39// invalid and report errors back. 40 41/* *** */ 42 43MCFragment::MCFragment() : Kind(FragmentType(~0)) { 44} 45 46MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent) 47 : Kind(_Kind), 48 Parent(_Parent), 49 FileSize(~UINT64_C(0)) 50{ 51 if (Parent) 52 Parent->getFragmentList().push_back(this); 53} 54 55MCFragment::~MCFragment() { 56} 57 58uint64_t MCFragment::getAddress() const { 59 assert(getParent() && "Missing Section!"); 60 return getParent()->getAddress() + Offset; 61} 62 63/* *** */ 64 65MCSectionData::MCSectionData() : Section(0) {} 66 67MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A) 68 : Section(&_Section), 69 Alignment(1), 70 Address(~UINT64_C(0)), 71 Size(~UINT64_C(0)), 72 FileSize(~UINT64_C(0)), 73 HasInstructions(false) 74{ 75 if (A) 76 A->getSectionList().push_back(this); 77} 78 79/* *** */ 80 81MCSymbolData::MCSymbolData() : Symbol(0) {} 82 83MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment, 84 uint64_t _Offset, MCAssembler *A) 85 : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset), 86 IsExternal(false), IsPrivateExtern(false), 87 CommonSize(0), CommonAlign(0), Flags(0), Index(0) 88{ 89 if (A) 90 A->getSymbolList().push_back(this); 91} 92 93/* *** */ 94 95MCAssembler::MCAssembler(MCContext &_Context, TargetAsmBackend &_Backend, 96 MCCodeEmitter &_Emitter, raw_ostream &_OS) 97 : Context(_Context), Backend(_Backend), Emitter(_Emitter), 98 OS(_OS), SubsectionsViaSymbols(false) 99{ 100} 101 102MCAssembler::~MCAssembler() { 103} 104 105static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm, 106 const MCAsmFixup &Fixup, 107 const MCDataFragment *DF, 108 const MCValue Target, 109 const MCSection *BaseSection) { 110 // The effective fixup address is 111 // addr(atom(A)) + offset(A) 112 // - addr(atom(B)) - offset(B) 113 // - addr(<base symbol>) + <fixup offset from base symbol> 114 // and the offsets are not relocatable, so the fixup is fully resolved when 115 // addr(atom(A)) - addr(atom(B)) - addr(<base symbol>)) == 0. 116 // 117 // The simple (Darwin, except on x86_64) way of dealing with this was to 118 // assume that any reference to a temporary symbol *must* be a temporary 119 // symbol in the same atom, unless the sections differ. Therefore, any PCrel 120 // relocation to a temporary symbol (in the same section) is fully 121 // resolved. This also works in conjunction with absolutized .set, which 122 // requires the compiler to use .set to absolutize the differences between 123 // symbols which the compiler knows to be assembly time constants, so we don't 124 // need to worry about consider symbol differences fully resolved. 125 126 // Non-relative fixups are only resolved if constant. 127 if (!BaseSection) 128 return Target.isAbsolute(); 129 130 // Otherwise, relative fixups are only resolved if not a difference and the 131 // target is a temporary in the same section. 132 if (Target.isAbsolute() || Target.getSymB()) 133 return false; 134 135 const MCSymbol *A = &Target.getSymA()->getSymbol(); 136 if (!A->isTemporary() || !A->isInSection() || 137 &A->getSection() != BaseSection) 138 return false; 139 140 return true; 141} 142 143static bool isScatteredFixupFullyResolved(const MCAssembler &Asm, 144 const MCAsmFixup &Fixup, 145 const MCDataFragment *DF, 146 const MCValue Target, 147 const MCSymbolData *BaseSymbol) { 148 // The effective fixup address is 149 // addr(atom(A)) + offset(A) 150 // - addr(atom(B)) - offset(B) 151 // - addr(BaseSymbol) + <fixup offset from base symbol> 152 // and the offsets are not relocatable, so the fixup is fully resolved when 153 // addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0. 154 // 155 // Note that "false" is almost always conservatively correct (it means we emit 156 // a relocation which is unnecessary), except when it would force us to emit a 157 // relocation which the target cannot encode. 158 159 const MCSymbolData *A_Base = 0, *B_Base = 0; 160 if (const MCSymbolRefExpr *A = Target.getSymA()) { 161 // Modified symbol references cannot be resolved. 162 if (A->getKind() != MCSymbolRefExpr::VK_None) 163 return false; 164 165 A_Base = Asm.getAtom(&Asm.getSymbolData(A->getSymbol())); 166 if (!A_Base) 167 return false; 168 } 169 170 if (const MCSymbolRefExpr *B = Target.getSymB()) { 171 // Modified symbol references cannot be resolved. 172 if (B->getKind() != MCSymbolRefExpr::VK_None) 173 return false; 174 175 B_Base = Asm.getAtom(&Asm.getSymbolData(B->getSymbol())); 176 if (!B_Base) 177 return false; 178 } 179 180 // If there is no base, A and B have to be the same atom for this fixup to be 181 // fully resolved. 182 if (!BaseSymbol) 183 return A_Base == B_Base; 184 185 // Otherwise, B must be missing and A must be the base. 186 return !B_Base && BaseSymbol == A_Base; 187} 188 189bool MCAssembler::isSymbolLinkerVisible(const MCSymbolData *SD) const { 190 // Non-temporary labels should always be visible to the linker. 191 if (!SD->getSymbol().isTemporary()) 192 return true; 193 194 // Absolute temporary labels are never visible. 195 if (!SD->getFragment()) 196 return false; 197 198 // Otherwise, check if the section requires symbols even for temporary labels. 199 return getBackend().doesSectionRequireSymbols( 200 SD->getFragment()->getParent()->getSection()); 201} 202 203const MCSymbolData *MCAssembler::getAtomForAddress(const MCSectionData *Section, 204 uint64_t Address) const { 205 const MCSymbolData *Best = 0; 206 for (MCAssembler::const_symbol_iterator it = symbol_begin(), 207 ie = symbol_end(); it != ie; ++it) { 208 // Ignore non-linker visible symbols. 209 if (!isSymbolLinkerVisible(it)) 210 continue; 211 212 // Ignore symbols not in the same section. 213 if (!it->getFragment() || it->getFragment()->getParent() != Section) 214 continue; 215 216 // Otherwise, find the closest symbol preceding this address (ties are 217 // resolved in favor of the last defined symbol). 218 if (it->getAddress() <= Address && 219 (!Best || it->getAddress() >= Best->getAddress())) 220 Best = it; 221 } 222 223 return Best; 224} 225 226const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const { 227 // Linker visible symbols define atoms. 228 if (isSymbolLinkerVisible(SD)) 229 return SD; 230 231 // Absolute and undefined symbols have no defining atom. 232 if (!SD->getFragment()) 233 return 0; 234 235 // Otherwise, search by address. 236 return getAtomForAddress(SD->getFragment()->getParent(), SD->getAddress()); 237} 238 239bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout, MCAsmFixup &Fixup, 240 MCDataFragment *DF, 241 MCValue &Target, uint64_t &Value) const { 242 if (!Fixup.Value->EvaluateAsRelocatable(Target, &Layout)) 243 llvm_report_error("expected relocatable expression"); 244 245 // FIXME: How do non-scattered symbols work in ELF? I presume the linker 246 // doesn't support small relocations, but then under what criteria does the 247 // assembler allow symbol differences? 248 249 Value = Target.getConstant(); 250 251 bool IsPCRel = 252 Emitter.getFixupKindInfo(Fixup.Kind).Flags & MCFixupKindInfo::FKF_IsPCRel; 253 bool IsResolved = true; 254 if (const MCSymbolRefExpr *A = Target.getSymA()) { 255 if (A->getSymbol().isDefined()) 256 Value += getSymbolData(A->getSymbol()).getAddress(); 257 else 258 IsResolved = false; 259 } 260 if (const MCSymbolRefExpr *B = Target.getSymB()) { 261 if (B->getSymbol().isDefined()) 262 Value -= getSymbolData(B->getSymbol()).getAddress(); 263 else 264 IsResolved = false; 265 } 266 267 // If we are using scattered symbols, determine whether this value is actually 268 // resolved; scattering may cause atoms to move. 269 if (IsResolved && getBackend().hasScatteredSymbols()) { 270 if (getBackend().hasReliableSymbolDifference()) { 271 // If this is a PCrel relocation, find the base atom (identified by its 272 // symbol) that the fixup value is relative to. 273 const MCSymbolData *BaseSymbol = 0; 274 if (IsPCRel) { 275 BaseSymbol = getAtomForAddress( 276 DF->getParent(), DF->getAddress() + Fixup.Offset); 277 if (!BaseSymbol) 278 IsResolved = false; 279 } 280 281 if (IsResolved) 282 IsResolved = isScatteredFixupFullyResolved(*this, Fixup, DF, Target, 283 BaseSymbol); 284 } else { 285 const MCSection *BaseSection = 0; 286 if (IsPCRel) 287 BaseSection = &DF->getParent()->getSection(); 288 289 IsResolved = isScatteredFixupFullyResolvedSimple(*this, Fixup, DF, Target, 290 BaseSection); 291 } 292 } 293 294 if (IsPCRel) 295 Value -= DF->getAddress() + Fixup.Offset; 296 297 return IsResolved; 298} 299 300void MCAssembler::LayoutSection(MCSectionData &SD) { 301 MCAsmLayout Layout(*this); 302 uint64_t Address = SD.getAddress(); 303 304 for (MCSectionData::iterator it = SD.begin(), ie = SD.end(); it != ie; ++it) { 305 MCFragment &F = *it; 306 307 F.setOffset(Address - SD.getAddress()); 308 309 // Evaluate fragment size. 310 switch (F.getKind()) { 311 case MCFragment::FT_Align: { 312 MCAlignFragment &AF = cast<MCAlignFragment>(F); 313 314 uint64_t Size = OffsetToAlignment(Address, AF.getAlignment()); 315 if (Size > AF.getMaxBytesToEmit()) 316 AF.setFileSize(0); 317 else 318 AF.setFileSize(Size); 319 break; 320 } 321 322 case MCFragment::FT_Data: 323 case MCFragment::FT_Fill: 324 F.setFileSize(F.getMaxFileSize()); 325 break; 326 327 case MCFragment::FT_Org: { 328 MCOrgFragment &OF = cast<MCOrgFragment>(F); 329 330 int64_t TargetLocation; 331 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, &Layout)) 332 llvm_report_error("expected assembly-time absolute expression"); 333 334 // FIXME: We need a way to communicate this error. 335 int64_t Offset = TargetLocation - F.getOffset(); 336 if (Offset < 0) 337 llvm_report_error("invalid .org offset '" + Twine(TargetLocation) + 338 "' (at offset '" + Twine(F.getOffset()) + "'"); 339 340 F.setFileSize(Offset); 341 break; 342 } 343 344 case MCFragment::FT_ZeroFill: { 345 MCZeroFillFragment &ZFF = cast<MCZeroFillFragment>(F); 346 347 // Align the fragment offset; it is safe to adjust the offset freely since 348 // this is only in virtual sections. 349 Address = RoundUpToAlignment(Address, ZFF.getAlignment()); 350 F.setOffset(Address - SD.getAddress()); 351 352 // FIXME: This is misnamed. 353 F.setFileSize(ZFF.getSize()); 354 break; 355 } 356 } 357 358 Address += F.getFileSize(); 359 } 360 361 // Set the section sizes. 362 SD.setSize(Address - SD.getAddress()); 363 if (getBackend().isVirtualSection(SD.getSection())) 364 SD.setFileSize(0); 365 else 366 SD.setFileSize(Address - SD.getAddress()); 367} 368 369/// WriteNopData - Write optimal nops to the output file for the \arg Count 370/// bytes. This returns the number of bytes written. It may return 0 if 371/// the \arg Count is more than the maximum optimal nops. 372/// 373/// FIXME this is X86 32-bit specific and should move to a better place. 374static uint64_t WriteNopData(uint64_t Count, MCObjectWriter *OW) { 375 static const uint8_t Nops[16][16] = { 376 // nop 377 {0x90}, 378 // xchg %ax,%ax 379 {0x66, 0x90}, 380 // nopl (%[re]ax) 381 {0x0f, 0x1f, 0x00}, 382 // nopl 0(%[re]ax) 383 {0x0f, 0x1f, 0x40, 0x00}, 384 // nopl 0(%[re]ax,%[re]ax,1) 385 {0x0f, 0x1f, 0x44, 0x00, 0x00}, 386 // nopw 0(%[re]ax,%[re]ax,1) 387 {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00}, 388 // nopl 0L(%[re]ax) 389 {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00}, 390 // nopl 0L(%[re]ax,%[re]ax,1) 391 {0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}, 392 // nopw 0L(%[re]ax,%[re]ax,1) 393 {0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}, 394 // nopw %cs:0L(%[re]ax,%[re]ax,1) 395 {0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}, 396 // nopl 0(%[re]ax,%[re]ax,1) 397 // nopw 0(%[re]ax,%[re]ax,1) 398 {0x0f, 0x1f, 0x44, 0x00, 0x00, 399 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00}, 400 // nopw 0(%[re]ax,%[re]ax,1) 401 // nopw 0(%[re]ax,%[re]ax,1) 402 {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00, 403 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00}, 404 // nopw 0(%[re]ax,%[re]ax,1) 405 // nopl 0L(%[re]ax) */ 406 {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00, 407 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00}, 408 // nopl 0L(%[re]ax) 409 // nopl 0L(%[re]ax) 410 {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00, 411 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00}, 412 // nopl 0L(%[re]ax) 413 // nopl 0L(%[re]ax,%[re]ax,1) 414 {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00, 415 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00} 416 }; 417 418 if (Count > 15) 419 return 0; 420 421 for (uint64_t i = 0; i < Count; i++) 422 OW->Write8(uint8_t(Nops[Count - 1][i])); 423 424 return Count; 425} 426 427/// WriteFragmentData - Write the \arg F data to the output file. 428static void WriteFragmentData(const MCFragment &F, MCObjectWriter *OW) { 429 uint64_t Start = OW->getStream().tell(); 430 (void) Start; 431 432 ++EmittedFragments; 433 434 // FIXME: Embed in fragments instead? 435 switch (F.getKind()) { 436 case MCFragment::FT_Align: { 437 MCAlignFragment &AF = cast<MCAlignFragment>(F); 438 uint64_t Count = AF.getFileSize() / AF.getValueSize(); 439 440 // FIXME: This error shouldn't actually occur (the front end should emit 441 // multiple .align directives to enforce the semantics it wants), but is 442 // severe enough that we want to report it. How to handle this? 443 if (Count * AF.getValueSize() != AF.getFileSize()) 444 llvm_report_error("undefined .align directive, value size '" + 445 Twine(AF.getValueSize()) + 446 "' is not a divisor of padding size '" + 447 Twine(AF.getFileSize()) + "'"); 448 449 // See if we are aligning with nops, and if so do that first to try to fill 450 // the Count bytes. Then if that did not fill any bytes or there are any 451 // bytes left to fill use the the Value and ValueSize to fill the rest. 452 if (AF.getEmitNops()) { 453 uint64_t NopByteCount = WriteNopData(Count, OW); 454 Count -= NopByteCount; 455 } 456 457 for (uint64_t i = 0; i != Count; ++i) { 458 switch (AF.getValueSize()) { 459 default: 460 assert(0 && "Invalid size!"); 461 case 1: OW->Write8 (uint8_t (AF.getValue())); break; 462 case 2: OW->Write16(uint16_t(AF.getValue())); break; 463 case 4: OW->Write32(uint32_t(AF.getValue())); break; 464 case 8: OW->Write64(uint64_t(AF.getValue())); break; 465 } 466 } 467 break; 468 } 469 470 case MCFragment::FT_Data: { 471 OW->WriteBytes(cast<MCDataFragment>(F).getContents().str()); 472 break; 473 } 474 475 case MCFragment::FT_Fill: { 476 MCFillFragment &FF = cast<MCFillFragment>(F); 477 for (uint64_t i = 0, e = FF.getCount(); i != e; ++i) { 478 switch (FF.getValueSize()) { 479 default: 480 assert(0 && "Invalid size!"); 481 case 1: OW->Write8 (uint8_t (FF.getValue())); break; 482 case 2: OW->Write16(uint16_t(FF.getValue())); break; 483 case 4: OW->Write32(uint32_t(FF.getValue())); break; 484 case 8: OW->Write64(uint64_t(FF.getValue())); break; 485 } 486 } 487 break; 488 } 489 490 case MCFragment::FT_Org: { 491 MCOrgFragment &OF = cast<MCOrgFragment>(F); 492 493 for (uint64_t i = 0, e = OF.getFileSize(); i != e; ++i) 494 OW->Write8(uint8_t(OF.getValue())); 495 496 break; 497 } 498 499 case MCFragment::FT_ZeroFill: { 500 assert(0 && "Invalid zero fill fragment in concrete section!"); 501 break; 502 } 503 } 504 505 assert(OW->getStream().tell() - Start == F.getFileSize()); 506} 507 508void MCAssembler::WriteSectionData(const MCSectionData *SD, 509 MCObjectWriter *OW) const { 510 // Ignore virtual sections. 511 if (getBackend().isVirtualSection(SD->getSection())) { 512 assert(SD->getFileSize() == 0); 513 return; 514 } 515 516 uint64_t Start = OW->getStream().tell(); 517 (void) Start; 518 519 for (MCSectionData::const_iterator it = SD->begin(), 520 ie = SD->end(); it != ie; ++it) 521 WriteFragmentData(*it, OW); 522 523 // Add section padding. 524 assert(SD->getFileSize() >= SD->getSize() && "Invalid section sizes!"); 525 OW->WriteZeros(SD->getFileSize() - SD->getSize()); 526 527 assert(OW->getStream().tell() - Start == SD->getFileSize()); 528} 529 530void MCAssembler::Finish() { 531 DEBUG_WITH_TYPE("mc-dump", { 532 llvm::errs() << "assembler backend - pre-layout\n--\n"; 533 dump(); }); 534 535 // Layout until everything fits. 536 while (LayoutOnce()) 537 continue; 538 539 DEBUG_WITH_TYPE("mc-dump", { 540 llvm::errs() << "assembler backend - post-layout\n--\n"; 541 dump(); }); 542 543 // FIXME: Factor out MCObjectWriter. 544 llvm::OwningPtr<MCObjectWriter> Writer(getBackend().createObjectWriter(OS)); 545 if (!Writer) 546 llvm_report_error("unable to create object writer!"); 547 548 // Allow the object writer a chance to perform post-layout binding (for 549 // example, to set the index fields in the symbol data). 550 Writer->ExecutePostLayoutBinding(*this); 551 552 // Evaluate and apply the fixups, generating relocation entries as necessary. 553 // 554 // FIXME: Share layout object. 555 MCAsmLayout Layout(*this); 556 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) { 557 for (MCSectionData::iterator it2 = it->begin(), 558 ie2 = it->end(); it2 != ie2; ++it2) { 559 MCDataFragment *DF = dyn_cast<MCDataFragment>(it2); 560 if (!DF) 561 continue; 562 563 for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(), 564 ie3 = DF->fixup_end(); it3 != ie3; ++it3) { 565 MCAsmFixup &Fixup = *it3; 566 567 // Evaluate the fixup. 568 MCValue Target; 569 uint64_t FixedValue; 570 if (!EvaluateFixup(Layout, Fixup, DF, Target, FixedValue)) { 571 // The fixup was unresolved, we need a relocation. Inform the object 572 // writer of the relocation, and give it an opportunity to adjust the 573 // fixup value if need be. 574 Writer->RecordRelocation(*this, *DF, Fixup, Target, FixedValue); 575 } 576 577 getBackend().ApplyFixup(Fixup, *DF, FixedValue); 578 } 579 } 580 } 581 582 // Write the object file. 583 Writer->WriteObject(*this); 584 OS.flush(); 585} 586 587bool MCAssembler::FixupNeedsRelaxation(MCAsmFixup &Fixup, MCDataFragment *DF) { 588 // FIXME: Share layout object. 589 MCAsmLayout Layout(*this); 590 591 // Currently we only need to relax X86::reloc_pcrel_1byte. 592 if (unsigned(Fixup.Kind) != X86::reloc_pcrel_1byte) 593 return false; 594 595 // If we cannot resolve the fixup value, it requires relaxation. 596 MCValue Target; 597 uint64_t Value; 598 if (!EvaluateFixup(Layout, Fixup, DF, Target, Value)) 599 return true; 600 601 // Otherwise, relax if the value is too big for a (signed) i8. 602 return int64_t(Value) != int64_t(int8_t(Value)); 603} 604 605bool MCAssembler::LayoutOnce() { 606 // Layout the concrete sections and fragments. 607 uint64_t Address = 0; 608 MCSectionData *Prev = 0; 609 for (iterator it = begin(), ie = end(); it != ie; ++it) { 610 MCSectionData &SD = *it; 611 612 // Skip virtual sections. 613 if (getBackend().isVirtualSection(SD.getSection())) 614 continue; 615 616 // Align this section if necessary by adding padding bytes to the previous 617 // section. 618 if (uint64_t Pad = OffsetToAlignment(Address, it->getAlignment())) { 619 assert(Prev && "Missing prev section!"); 620 Prev->setFileSize(Prev->getFileSize() + Pad); 621 Address += Pad; 622 } 623 624 // Layout the section fragments and its size. 625 SD.setAddress(Address); 626 LayoutSection(SD); 627 Address += SD.getFileSize(); 628 629 Prev = &SD; 630 } 631 632 // Layout the virtual sections. 633 for (iterator it = begin(), ie = end(); it != ie; ++it) { 634 MCSectionData &SD = *it; 635 636 if (!getBackend().isVirtualSection(SD.getSection())) 637 continue; 638 639 // Align this section if necessary by adding padding bytes to the previous 640 // section. 641 if (uint64_t Pad = OffsetToAlignment(Address, it->getAlignment())) 642 Address += Pad; 643 644 SD.setAddress(Address); 645 LayoutSection(SD); 646 Address += SD.getSize(); 647 } 648 649 // Scan the fixups in order and relax any that don't fit. 650 for (iterator it = begin(), ie = end(); it != ie; ++it) { 651 MCSectionData &SD = *it; 652 653 for (MCSectionData::iterator it2 = SD.begin(), 654 ie2 = SD.end(); it2 != ie2; ++it2) { 655 MCDataFragment *DF = dyn_cast<MCDataFragment>(it2); 656 if (!DF) 657 continue; 658 659 for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(), 660 ie3 = DF->fixup_end(); it3 != ie3; ++it3) { 661 MCAsmFixup &Fixup = *it3; 662 663 // Check whether we need to relax this fixup. 664 if (!FixupNeedsRelaxation(Fixup, DF)) 665 continue; 666 667 // Relax the instruction. 668 // 669 // FIXME: This is a huge temporary hack which just looks for x86 670 // branches; the only thing we need to relax on x86 is 671 // 'X86::reloc_pcrel_1byte'. Once we have MCInst fragments, this will be 672 // replaced by a TargetAsmBackend hook (most likely tblgen'd) to relax 673 // an individual MCInst. 674 SmallVectorImpl<char> &C = DF->getContents(); 675 uint64_t PrevOffset = Fixup.Offset; 676 unsigned Amt = 0; 677 678 // jcc instructions 679 if (unsigned(C[Fixup.Offset-1]) >= 0x70 && 680 unsigned(C[Fixup.Offset-1]) <= 0x7f) { 681 C[Fixup.Offset] = C[Fixup.Offset-1] + 0x10; 682 C[Fixup.Offset-1] = char(0x0f); 683 ++Fixup.Offset; 684 Amt = 4; 685 686 // jmp rel8 687 } else if (C[Fixup.Offset-1] == char(0xeb)) { 688 C[Fixup.Offset-1] = char(0xe9); 689 Amt = 3; 690 691 } else 692 llvm_unreachable("unknown 1 byte pcrel instruction!"); 693 694 Fixup.Value = MCBinaryExpr::Create( 695 MCBinaryExpr::Sub, Fixup.Value, 696 MCConstantExpr::Create(3, getContext()), 697 getContext()); 698 C.insert(C.begin() + Fixup.Offset, Amt, char(0)); 699 Fixup.Kind = MCFixupKind(X86::reloc_pcrel_4byte); 700 701 // Update the remaining fixups, which have slid. 702 // 703 // FIXME: This is bad for performance, but will be eliminated by the 704 // move to MCInst specific fragments. 705 ++it3; 706 for (; it3 != ie3; ++it3) 707 it3->Offset += Amt; 708 709 // Update all the symbols for this fragment, which may have slid. 710 // 711 // FIXME: This is really really bad for performance, but will be 712 // eliminated by the move to MCInst specific fragments. 713 for (MCAssembler::symbol_iterator it = symbol_begin(), 714 ie = symbol_end(); it != ie; ++it) { 715 MCSymbolData &SD = *it; 716 717 if (it->getFragment() != DF) 718 continue; 719 720 if (SD.getOffset() > PrevOffset) 721 SD.setOffset(SD.getOffset() + Amt); 722 } 723 724 // Restart layout. 725 // 726 // FIXME: This is O(N^2), but will be eliminated once we have a smart 727 // MCAsmLayout object. 728 return true; 729 } 730 } 731 } 732 733 return false; 734} 735 736// Debugging methods 737 738namespace llvm { 739 740raw_ostream &operator<<(raw_ostream &OS, const MCAsmFixup &AF) { 741 OS << "<MCAsmFixup" << " Offset:" << AF.Offset << " Value:" << *AF.Value 742 << " Kind:" << AF.Kind << ">"; 743 return OS; 744} 745 746} 747 748void MCFragment::dump() { 749 raw_ostream &OS = llvm::errs(); 750 751 OS << "<MCFragment " << (void*) this << " Offset:" << Offset 752 << " FileSize:" << FileSize; 753 754 OS << ">"; 755} 756 757void MCAlignFragment::dump() { 758 raw_ostream &OS = llvm::errs(); 759 760 OS << "<MCAlignFragment "; 761 this->MCFragment::dump(); 762 OS << "\n "; 763 OS << " Alignment:" << getAlignment() 764 << " Value:" << getValue() << " ValueSize:" << getValueSize() 765 << " MaxBytesToEmit:" << getMaxBytesToEmit() << ">"; 766} 767 768void MCDataFragment::dump() { 769 raw_ostream &OS = llvm::errs(); 770 771 OS << "<MCDataFragment "; 772 this->MCFragment::dump(); 773 OS << "\n "; 774 OS << " Contents:["; 775 for (unsigned i = 0, e = getContents().size(); i != e; ++i) { 776 if (i) OS << ","; 777 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF); 778 } 779 OS << "] (" << getContents().size() << " bytes)"; 780 781 if (!getFixups().empty()) { 782 OS << ",\n "; 783 OS << " Fixups:["; 784 for (fixup_iterator it = fixup_begin(), ie = fixup_end(); it != ie; ++it) { 785 if (it != fixup_begin()) OS << ",\n "; 786 OS << *it; 787 } 788 OS << "]"; 789 } 790 791 OS << ">"; 792} 793 794void MCFillFragment::dump() { 795 raw_ostream &OS = llvm::errs(); 796 797 OS << "<MCFillFragment "; 798 this->MCFragment::dump(); 799 OS << "\n "; 800 OS << " Value:" << getValue() << " ValueSize:" << getValueSize() 801 << " Count:" << getCount() << ">"; 802} 803 804void MCOrgFragment::dump() { 805 raw_ostream &OS = llvm::errs(); 806 807 OS << "<MCOrgFragment "; 808 this->MCFragment::dump(); 809 OS << "\n "; 810 OS << " Offset:" << getOffset() << " Value:" << getValue() << ">"; 811} 812 813void MCZeroFillFragment::dump() { 814 raw_ostream &OS = llvm::errs(); 815 816 OS << "<MCZeroFillFragment "; 817 this->MCFragment::dump(); 818 OS << "\n "; 819 OS << " Size:" << getSize() << " Alignment:" << getAlignment() << ">"; 820} 821 822void MCSectionData::dump() { 823 raw_ostream &OS = llvm::errs(); 824 825 OS << "<MCSectionData"; 826 OS << " Alignment:" << getAlignment() << " Address:" << Address 827 << " Size:" << Size << " FileSize:" << FileSize 828 << " Fragments:[\n "; 829 for (iterator it = begin(), ie = end(); it != ie; ++it) { 830 if (it != begin()) OS << ",\n "; 831 it->dump(); 832 } 833 OS << "]>"; 834} 835 836void MCSymbolData::dump() { 837 raw_ostream &OS = llvm::errs(); 838 839 OS << "<MCSymbolData Symbol:" << getSymbol() 840 << " Fragment:" << getFragment() << " Offset:" << getOffset() 841 << " Flags:" << getFlags() << " Index:" << getIndex(); 842 if (isCommon()) 843 OS << " (common, size:" << getCommonSize() 844 << " align: " << getCommonAlignment() << ")"; 845 if (isExternal()) 846 OS << " (external)"; 847 if (isPrivateExtern()) 848 OS << " (private extern)"; 849 OS << ">"; 850} 851 852void MCAssembler::dump() { 853 raw_ostream &OS = llvm::errs(); 854 855 OS << "<MCAssembler\n"; 856 OS << " Sections:[\n "; 857 for (iterator it = begin(), ie = end(); it != ie; ++it) { 858 if (it != begin()) OS << ",\n "; 859 it->dump(); 860 } 861 OS << "],\n"; 862 OS << " Symbols:["; 863 864 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) { 865 if (it != symbol_begin()) OS << ",\n "; 866 it->dump(); 867 } 868 OS << "]>\n"; 869} 870