1 //===- lib/MC/MachObjectWriter.cpp - Mach-O File Writer -------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #include "llvm/ADT/StringMap.h"
11 #include "llvm/ADT/Twine.h"
12 #include "llvm/MC/MCAssembler.h"
13 #include "llvm/MC/MCAsmLayout.h"
14 #include "llvm/MC/MCExpr.h"
15 #include "llvm/MC/MCObjectWriter.h"
16 #include "llvm/MC/MCSectionMachO.h"
17 #include "llvm/MC/MCSymbol.h"
18 #include "llvm/MC/MCMachOSymbolFlags.h"
19 #include "llvm/MC/MCValue.h"
20 #include "llvm/Object/MachOFormat.h"
21 #include "llvm/Support/ErrorHandling.h"
22 #include "llvm/Target/TargetAsmBackend.h"
25 #include "../Target/X86/X86FixupKinds.h"
29 using namespace llvm::object;
31 // FIXME: this has been copied from (or to) X86AsmBackend.cpp
32 static unsigned getFixupKindLog2Size(unsigned Kind) {
34 // FIXME: Until ARM has it's own relocation stuff spun off, it comes
35 // through here and we don't want it to puke all over. Any reasonable
36 // values will only come when ARM relocation support gets added, at which
37 // point this will be X86 only again and the llvm_unreachable can be
39 default: return 0;// llvm_unreachable("invalid fixup kind!");
41 case FK_Data_1: return 0;
43 case FK_Data_2: return 1;
45 case X86::reloc_riprel_4byte:
46 case X86::reloc_riprel_4byte_movq_load:
47 case X86::reloc_signed_4byte:
48 case FK_Data_4: return 2;
49 case FK_Data_8: return 3;
53 static bool isFixupKindPCRel(unsigned Kind) {
60 case X86::reloc_riprel_4byte:
61 case X86::reloc_riprel_4byte_movq_load:
66 static bool isFixupKindRIPRel(unsigned Kind) {
67 return Kind == X86::reloc_riprel_4byte ||
68 Kind == X86::reloc_riprel_4byte_movq_load;
71 static bool doesSymbolRequireExternRelocation(MCSymbolData *SD) {
72 // Undefined symbols are always extern.
73 if (SD->Symbol->isUndefined())
76 // References to weak definitions require external relocation entries; the
77 // definition may not always be the one in the same object file.
78 if (SD->getFlags() & SF_WeakDefinition)
81 // Otherwise, we can use an internal relocation.
85 static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
87 const MCSymbolData *BaseSymbol) {
88 // The effective fixup address is
89 // addr(atom(A)) + offset(A)
90 // - addr(atom(B)) - offset(B)
91 // - addr(BaseSymbol) + <fixup offset from base symbol>
92 // and the offsets are not relocatable, so the fixup is fully resolved when
93 // addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
95 // Note that "false" is almost always conservatively correct (it means we emit
96 // a relocation which is unnecessary), except when it would force us to emit a
97 // relocation which the target cannot encode.
99 const MCSymbolData *A_Base = 0, *B_Base = 0;
100 if (const MCSymbolRefExpr *A = Target.getSymA()) {
101 // Modified symbol references cannot be resolved.
102 if (A->getKind() != MCSymbolRefExpr::VK_None)
105 A_Base = Asm.getAtom(&Asm.getSymbolData(A->getSymbol()));
110 if (const MCSymbolRefExpr *B = Target.getSymB()) {
111 // Modified symbol references cannot be resolved.
112 if (B->getKind() != MCSymbolRefExpr::VK_None)
115 B_Base = Asm.getAtom(&Asm.getSymbolData(B->getSymbol()));
120 // If there is no base, A and B have to be the same atom for this fixup to be
123 return A_Base == B_Base;
125 // Otherwise, B must be missing and A must be the base.
126 return !B_Base && BaseSymbol == A_Base;
129 static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm,
130 const MCValue Target,
131 const MCSection *BaseSection) {
132 // The effective fixup address is
133 // addr(atom(A)) + offset(A)
134 // - addr(atom(B)) - offset(B)
135 // - addr(<base symbol>) + <fixup offset from base symbol>
136 // and the offsets are not relocatable, so the fixup is fully resolved when
137 // addr(atom(A)) - addr(atom(B)) - addr(<base symbol>)) == 0.
139 // The simple (Darwin, except on x86_64) way of dealing with this was to
140 // assume that any reference to a temporary symbol *must* be a temporary
141 // symbol in the same atom, unless the sections differ. Therefore, any PCrel
142 // relocation to a temporary symbol (in the same section) is fully
143 // resolved. This also works in conjunction with absolutized .set, which
144 // requires the compiler to use .set to absolutize the differences between
145 // symbols which the compiler knows to be assembly time constants, so we don't
146 // need to worry about considering symbol differences fully resolved.
148 // Non-relative fixups are only resolved if constant.
150 return Target.isAbsolute();
152 // Otherwise, relative fixups are only resolved if not a difference and the
153 // target is a temporary in the same section.
154 if (Target.isAbsolute() || Target.getSymB())
157 const MCSymbol *A = &Target.getSymA()->getSymbol();
158 if (!A->isTemporary() || !A->isInSection() ||
159 &A->getSection() != BaseSection)
167 class MachObjectWriter : public MCObjectWriter {
168 /// MachSymbolData - Helper struct for containing some precomputed information
170 struct MachSymbolData {
171 MCSymbolData *SymbolData;
172 uint64_t StringIndex;
173 uint8_t SectionIndex;
175 // Support lexicographic sorting.
176 bool operator<(const MachSymbolData &RHS) const {
177 return SymbolData->getSymbol().getName() <
178 RHS.SymbolData->getSymbol().getName();
182 /// @name Relocation Data
185 llvm::DenseMap<const MCSectionData*,
186 std::vector<macho::RelocationEntry> > Relocations;
187 llvm::DenseMap<const MCSectionData*, unsigned> IndirectSymBase;
190 /// @name Symbol Table Data
193 SmallString<256> StringTable;
194 std::vector<MachSymbolData> LocalSymbolData;
195 std::vector<MachSymbolData> ExternalSymbolData;
196 std::vector<MachSymbolData> UndefinedSymbolData;
200 SectionAddrMap SectionAddress;
201 uint64_t getSectionAddress(const MCSectionData* SD) const {
202 return SectionAddress.lookup(SD);
204 uint64_t getSymbolAddress(const MCSymbolData* SD,
205 const MCAsmLayout &Layout) const {
206 return getSectionAddress(SD->getFragment()->getParent()) +
207 Layout.getSymbolOffset(SD);
209 uint64_t getFragmentAddress(const MCFragment *Fragment,
210 const MCAsmLayout &Layout) const {
211 return getSectionAddress(Fragment->getParent()) +
212 Layout.getFragmentOffset(Fragment);
215 uint64_t getPaddingSize(const MCSectionData *SD,
216 const MCAsmLayout &Layout) const {
217 uint64_t EndAddr = getSectionAddress(SD) + Layout.getSectionAddressSize(SD);
218 unsigned Next = SD->getLayoutOrder() + 1;
219 if (Next >= Layout.getSectionOrder().size())
222 const MCSectionData &NextSD = *Layout.getSectionOrder()[Next];
223 if (NextSD.getSection().isVirtualSection())
225 return OffsetToAlignment(EndAddr, NextSD.getAlignment());
228 unsigned Is64Bit : 1;
234 MachObjectWriter(raw_ostream &_OS,
235 bool _Is64Bit, uint32_t _CPUType, uint32_t _CPUSubtype,
236 bool _IsLittleEndian)
237 : MCObjectWriter(_OS, _IsLittleEndian),
238 Is64Bit(_Is64Bit), CPUType(_CPUType), CPUSubtype(_CPUSubtype) {
241 void WriteHeader(unsigned NumLoadCommands, unsigned LoadCommandsSize,
242 bool SubsectionsViaSymbols) {
245 if (SubsectionsViaSymbols)
246 Flags |= macho::HF_SubsectionsViaSymbols;
248 // struct mach_header (28 bytes) or
249 // struct mach_header_64 (32 bytes)
251 uint64_t Start = OS.tell();
254 Write32(Is64Bit ? macho::HM_Object64 : macho::HM_Object32);
259 Write32(macho::HFT_Object);
260 Write32(NumLoadCommands);
261 Write32(LoadCommandsSize);
264 Write32(0); // reserved
266 assert(OS.tell() - Start == Is64Bit ?
267 macho::Header64Size : macho::Header32Size);
270 /// WriteSegmentLoadCommand - Write a segment load command.
272 /// \arg NumSections - The number of sections in this segment.
273 /// \arg SectionDataSize - The total size of the sections.
274 void WriteSegmentLoadCommand(unsigned NumSections,
276 uint64_t SectionDataStartOffset,
277 uint64_t SectionDataSize) {
278 // struct segment_command (56 bytes) or
279 // struct segment_command_64 (72 bytes)
281 uint64_t Start = OS.tell();
284 unsigned SegmentLoadCommandSize = Is64Bit ? macho::SegmentLoadCommand64Size:
285 macho::SegmentLoadCommand32Size;
286 Write32(Is64Bit ? macho::LCT_Segment64 : macho::LCT_Segment);
287 Write32(SegmentLoadCommandSize +
288 NumSections * (Is64Bit ? macho::Section64Size :
289 macho::Section32Size));
293 Write64(0); // vmaddr
294 Write64(VMSize); // vmsize
295 Write64(SectionDataStartOffset); // file offset
296 Write64(SectionDataSize); // file size
298 Write32(0); // vmaddr
299 Write32(VMSize); // vmsize
300 Write32(SectionDataStartOffset); // file offset
301 Write32(SectionDataSize); // file size
303 Write32(0x7); // maxprot
304 Write32(0x7); // initprot
305 Write32(NumSections);
308 assert(OS.tell() - Start == SegmentLoadCommandSize);
311 void WriteSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
312 const MCSectionData &SD, uint64_t FileOffset,
313 uint64_t RelocationsStart, unsigned NumRelocations) {
314 uint64_t SectionSize = Layout.getSectionAddressSize(&SD);
316 // The offset is unused for virtual sections.
317 if (SD.getSection().isVirtualSection()) {
318 assert(Layout.getSectionFileSize(&SD) == 0 && "Invalid file size!");
322 // struct section (68 bytes) or
323 // struct section_64 (80 bytes)
325 uint64_t Start = OS.tell();
328 const MCSectionMachO &Section = cast<MCSectionMachO>(SD.getSection());
329 WriteBytes(Section.getSectionName(), 16);
330 WriteBytes(Section.getSegmentName(), 16);
332 Write64(getSectionAddress(&SD)); // address
333 Write64(SectionSize); // size
335 Write32(getSectionAddress(&SD)); // address
336 Write32(SectionSize); // size
340 unsigned Flags = Section.getTypeAndAttributes();
341 if (SD.hasInstructions())
342 Flags |= MCSectionMachO::S_ATTR_SOME_INSTRUCTIONS;
344 assert(isPowerOf2_32(SD.getAlignment()) && "Invalid alignment!");
345 Write32(Log2_32(SD.getAlignment()));
346 Write32(NumRelocations ? RelocationsStart : 0);
347 Write32(NumRelocations);
349 Write32(IndirectSymBase.lookup(&SD)); // reserved1
350 Write32(Section.getStubSize()); // reserved2
352 Write32(0); // reserved3
354 assert(OS.tell() - Start == Is64Bit ? macho::Section64Size :
355 macho::Section32Size);
358 void WriteSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
359 uint32_t StringTableOffset,
360 uint32_t StringTableSize) {
361 // struct symtab_command (24 bytes)
363 uint64_t Start = OS.tell();
366 Write32(macho::LCT_Symtab);
367 Write32(macho::SymtabLoadCommandSize);
368 Write32(SymbolOffset);
370 Write32(StringTableOffset);
371 Write32(StringTableSize);
373 assert(OS.tell() - Start == macho::SymtabLoadCommandSize);
376 void WriteDysymtabLoadCommand(uint32_t FirstLocalSymbol,
377 uint32_t NumLocalSymbols,
378 uint32_t FirstExternalSymbol,
379 uint32_t NumExternalSymbols,
380 uint32_t FirstUndefinedSymbol,
381 uint32_t NumUndefinedSymbols,
382 uint32_t IndirectSymbolOffset,
383 uint32_t NumIndirectSymbols) {
384 // struct dysymtab_command (80 bytes)
386 uint64_t Start = OS.tell();
389 Write32(macho::LCT_Dysymtab);
390 Write32(macho::DysymtabLoadCommandSize);
391 Write32(FirstLocalSymbol);
392 Write32(NumLocalSymbols);
393 Write32(FirstExternalSymbol);
394 Write32(NumExternalSymbols);
395 Write32(FirstUndefinedSymbol);
396 Write32(NumUndefinedSymbols);
397 Write32(0); // tocoff
399 Write32(0); // modtaboff
400 Write32(0); // nmodtab
401 Write32(0); // extrefsymoff
402 Write32(0); // nextrefsyms
403 Write32(IndirectSymbolOffset);
404 Write32(NumIndirectSymbols);
405 Write32(0); // extreloff
406 Write32(0); // nextrel
407 Write32(0); // locreloff
408 Write32(0); // nlocrel
410 assert(OS.tell() - Start == macho::DysymtabLoadCommandSize);
413 void WriteNlist(MachSymbolData &MSD, const MCAsmLayout &Layout) {
414 MCSymbolData &Data = *MSD.SymbolData;
415 const MCSymbol &Symbol = Data.getSymbol();
417 uint16_t Flags = Data.getFlags();
418 uint32_t Address = 0;
420 // Set the N_TYPE bits. See <mach-o/nlist.h>.
422 // FIXME: Are the prebound or indirect fields possible here?
423 if (Symbol.isUndefined())
424 Type = macho::STT_Undefined;
425 else if (Symbol.isAbsolute())
426 Type = macho::STT_Absolute;
428 Type = macho::STT_Section;
430 // FIXME: Set STAB bits.
432 if (Data.isPrivateExtern())
433 Type |= macho::STF_PrivateExtern;
436 if (Data.isExternal() || Symbol.isUndefined())
437 Type |= macho::STF_External;
439 // Compute the symbol address.
440 if (Symbol.isDefined()) {
441 if (Symbol.isAbsolute()) {
442 Address = cast<MCConstantExpr>(Symbol.getVariableValue())->getValue();
444 Address = getSymbolAddress(&Data, Layout);
446 } else if (Data.isCommon()) {
447 // Common symbols are encoded with the size in the address
448 // field, and their alignment in the flags.
449 Address = Data.getCommonSize();
451 // Common alignment is packed into the 'desc' bits.
452 if (unsigned Align = Data.getCommonAlignment()) {
453 unsigned Log2Size = Log2_32(Align);
454 assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
456 report_fatal_error("invalid 'common' alignment '" +
458 // FIXME: Keep this mask with the SymbolFlags enumeration.
459 Flags = (Flags & 0xF0FF) | (Log2Size << 8);
463 // struct nlist (12 bytes)
465 Write32(MSD.StringIndex);
467 Write8(MSD.SectionIndex);
469 // The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
478 // FIXME: We really need to improve the relocation validation. Basically, we
479 // want to implement a separate computation which evaluates the relocation
480 // entry as the linker would, and verifies that the resultant fixup value is
481 // exactly what the encoder wanted. This will catch several classes of
484 // - Relocation entry bugs, the two algorithms are unlikely to have the same
487 // - Relaxation issues, where we forget to relax something.
489 // - Input errors, where something cannot be correctly encoded. 'as' allows
490 // these through in many cases.
492 void RecordX86_64Relocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
493 const MCFragment *Fragment,
494 const MCFixup &Fixup, MCValue Target,
495 uint64_t &FixedValue) {
496 unsigned IsPCRel = isFixupKindPCRel(Fixup.getKind());
497 unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind());
498 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
501 uint32_t FixupOffset =
502 Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
503 uint32_t FixupAddress =
504 getFragmentAddress(Fragment, Layout) + Fixup.getOffset();
507 unsigned IsExtern = 0;
510 Value = Target.getConstant();
513 // Compensate for the relocation offset, Darwin x86_64 relocations only
514 // have the addend and appear to have attempted to define it to be the
515 // actual expression addend without the PCrel bias. However, instructions
516 // with data following the relocation are not accomodated for (see comment
517 // below regarding SIGNED{1,2,4}), so it isn't exactly that either.
518 Value += 1LL << Log2Size;
521 if (Target.isAbsolute()) { // constant
522 // SymbolNum of 0 indicates the absolute section.
523 Type = macho::RIT_X86_64_Unsigned;
526 // FIXME: I believe this is broken, I don't think the linker can
527 // understand it. I think it would require a local relocation, but I'm not
528 // sure if that would work either. The official way to get an absolute
529 // PCrel relocation is to use an absolute symbol (which we don't support
533 Type = macho::RIT_X86_64_Branch;
535 } else if (Target.getSymB()) { // A - B + constant
536 const MCSymbol *A = &Target.getSymA()->getSymbol();
537 MCSymbolData &A_SD = Asm.getSymbolData(*A);
538 const MCSymbolData *A_Base = Asm.getAtom(&A_SD);
540 const MCSymbol *B = &Target.getSymB()->getSymbol();
541 MCSymbolData &B_SD = Asm.getSymbolData(*B);
542 const MCSymbolData *B_Base = Asm.getAtom(&B_SD);
544 // Neither symbol can be modified.
545 if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
546 Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
547 report_fatal_error("unsupported relocation of modified symbol");
549 // We don't support PCrel relocations of differences. Darwin 'as' doesn't
550 // implement most of these correctly.
552 report_fatal_error("unsupported pc-relative relocation of difference");
554 // The support for the situation where one or both of the symbols would
555 // require a local relocation is handled just like if the symbols were
556 // external. This is certainly used in the case of debug sections where
557 // the section has only temporary symbols and thus the symbols don't have
558 // base symbols. This is encoded using the section ordinal and
559 // non-extern relocation entries.
561 // Darwin 'as' doesn't emit correct relocations for this (it ends up with
562 // a single SIGNED relocation); reject it for now. Except the case where
563 // both symbols don't have a base, equal but both NULL.
564 if (A_Base == B_Base && A_Base)
565 report_fatal_error("unsupported relocation with identical base");
567 Value += getSymbolAddress(&A_SD, Layout) -
568 (A_Base == NULL ? 0 : getSymbolAddress(A_Base, Layout));
569 Value -= getSymbolAddress(&B_SD, Layout) -
570 (B_Base == NULL ? 0 : getSymbolAddress(B_Base, Layout));
573 Index = A_Base->getIndex();
577 Index = A_SD.getFragment()->getParent()->getOrdinal() + 1;
580 Type = macho::RIT_X86_64_Unsigned;
582 macho::RelocationEntry MRE;
583 MRE.Word0 = FixupOffset;
584 MRE.Word1 = ((Index << 0) |
589 Relocations[Fragment->getParent()].push_back(MRE);
592 Index = B_Base->getIndex();
596 Index = B_SD.getFragment()->getParent()->getOrdinal() + 1;
599 Type = macho::RIT_X86_64_Subtractor;
601 const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
602 MCSymbolData &SD = Asm.getSymbolData(*Symbol);
603 const MCSymbolData *Base = Asm.getAtom(&SD);
605 // Relocations inside debug sections always use local relocations when
606 // possible. This seems to be done because the debugger doesn't fully
607 // understand x86_64 relocation entries, and expects to find values that
608 // have already been fixed up.
609 if (Symbol->isInSection()) {
610 const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
611 Fragment->getParent()->getSection());
612 if (Section.hasAttribute(MCSectionMachO::S_ATTR_DEBUG))
616 // x86_64 almost always uses external relocations, except when there is no
617 // symbol to use as a base address (a local symbol with no preceeding
618 // non-local symbol).
620 Index = Base->getIndex();
623 // Add the local offset, if needed.
625 Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base);
626 } else if (Symbol->isInSection()) {
627 // The index is the section ordinal (1-based).
628 Index = SD.getFragment()->getParent()->getOrdinal() + 1;
630 Value += getSymbolAddress(&SD, Layout);
633 Value -= FixupAddress + (1 << Log2Size);
634 } else if (Symbol->isVariable()) {
635 const MCExpr *Value = Symbol->getVariableValue();
637 bool isAbs = Value->EvaluateAsAbsolute(Res, Layout, SectionAddress);
642 report_fatal_error("unsupported relocation of variable '" +
643 Symbol->getName() + "'");
646 report_fatal_error("unsupported relocation of undefined symbol '" +
647 Symbol->getName() + "'");
650 MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
653 if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
654 // x86_64 distinguishes movq foo@GOTPCREL so that the linker can
655 // rewrite the movq to an leaq at link time if the symbol ends up in
656 // the same linkage unit.
657 if (unsigned(Fixup.getKind()) == X86::reloc_riprel_4byte_movq_load)
658 Type = macho::RIT_X86_64_GOTLoad;
660 Type = macho::RIT_X86_64_GOT;
661 } else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
662 Type = macho::RIT_X86_64_TLV;
663 } else if (Modifier != MCSymbolRefExpr::VK_None) {
664 report_fatal_error("unsupported symbol modifier in relocation");
666 Type = macho::RIT_X86_64_Signed;
668 // The Darwin x86_64 relocation format has a problem where it cannot
669 // encode an address (L<foo> + <constant>) which is outside the atom
670 // containing L<foo>. Generally, this shouldn't occur but it does
671 // happen when we have a RIPrel instruction with data following the
672 // relocation entry (e.g., movb $012, L0(%rip)). Even with the PCrel
673 // adjustment Darwin x86_64 uses, the offset is still negative and
674 // the linker has no way to recognize this.
676 // To work around this, Darwin uses several special relocation types
677 // to indicate the offsets. However, the specification or
678 // implementation of these seems to also be incomplete; they should
679 // adjust the addend as well based on the actual encoded instruction
680 // (the additional bias), but instead appear to just look at the
682 switch (-(Target.getConstant() + (1LL << Log2Size))) {
683 case 1: Type = macho::RIT_X86_64_Signed1; break;
684 case 2: Type = macho::RIT_X86_64_Signed2; break;
685 case 4: Type = macho::RIT_X86_64_Signed4; break;
689 if (Modifier != MCSymbolRefExpr::VK_None)
690 report_fatal_error("unsupported symbol modifier in branch "
693 Type = macho::RIT_X86_64_Branch;
696 if (Modifier == MCSymbolRefExpr::VK_GOT) {
697 Type = macho::RIT_X86_64_GOT;
698 } else if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
699 // GOTPCREL is allowed as a modifier on non-PCrel instructions, in
700 // which case all we do is set the PCrel bit in the relocation entry;
701 // this is used with exception handling, for example. The source is
702 // required to include any necessary offset directly.
703 Type = macho::RIT_X86_64_GOT;
705 } else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
706 report_fatal_error("TLVP symbol modifier should have been rip-rel");
707 } else if (Modifier != MCSymbolRefExpr::VK_None)
708 report_fatal_error("unsupported symbol modifier in relocation");
710 Type = macho::RIT_X86_64_Unsigned;
714 // x86_64 always writes custom values into the fixups.
717 // struct relocation_info (8 bytes)
718 macho::RelocationEntry MRE;
719 MRE.Word0 = FixupOffset;
720 MRE.Word1 = ((Index << 0) |
725 Relocations[Fragment->getParent()].push_back(MRE);
728 void RecordScatteredRelocation(const MCAssembler &Asm,
729 const MCAsmLayout &Layout,
730 const MCFragment *Fragment,
731 const MCFixup &Fixup, MCValue Target,
732 uint64_t &FixedValue) {
733 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
734 unsigned IsPCRel = isFixupKindPCRel(Fixup.getKind());
735 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
736 unsigned Type = macho::RIT_Vanilla;
739 const MCSymbol *A = &Target.getSymA()->getSymbol();
740 MCSymbolData *A_SD = &Asm.getSymbolData(*A);
742 if (!A_SD->getFragment())
743 report_fatal_error("symbol '" + A->getName() +
744 "' can not be undefined in a subtraction expression");
746 uint32_t Value = getSymbolAddress(A_SD, Layout);
747 uint64_t SecAddr = getSectionAddress(A_SD->getFragment()->getParent());
748 FixedValue += SecAddr;
751 if (const MCSymbolRefExpr *B = Target.getSymB()) {
752 MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
754 if (!B_SD->getFragment())
755 report_fatal_error("symbol '" + B->getSymbol().getName() +
756 "' can not be undefined in a subtraction expression");
758 // Select the appropriate difference relocation type.
760 // Note that there is no longer any semantic difference between these two
761 // relocation types from the linkers point of view, this is done solely
762 // for pedantic compatibility with 'as'.
763 Type = A_SD->isExternal() ? macho::RIT_Difference :
764 macho::RIT_LocalDifference;
765 Value2 = getSymbolAddress(B_SD, Layout);
766 FixedValue -= getSectionAddress(B_SD->getFragment()->getParent());
769 // Relocations are written out in reverse order, so the PAIR comes first.
770 if (Type == macho::RIT_Difference || Type == macho::RIT_LocalDifference) {
771 macho::RelocationEntry MRE;
772 MRE.Word0 = ((0 << 0) |
773 (macho::RIT_Pair << 24) |
776 macho::RF_Scattered);
778 Relocations[Fragment->getParent()].push_back(MRE);
781 macho::RelocationEntry MRE;
782 MRE.Word0 = ((FixupOffset << 0) |
786 macho::RF_Scattered);
788 Relocations[Fragment->getParent()].push_back(MRE);
791 void RecordTLVPRelocation(const MCAssembler &Asm,
792 const MCAsmLayout &Layout,
793 const MCFragment *Fragment,
794 const MCFixup &Fixup, MCValue Target,
795 uint64_t &FixedValue) {
796 assert(Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP &&
798 "Should only be called with a 32-bit TLVP relocation!");
800 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
801 uint32_t Value = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
802 unsigned IsPCRel = 0;
804 // Get the symbol data.
805 MCSymbolData *SD_A = &Asm.getSymbolData(Target.getSymA()->getSymbol());
806 unsigned Index = SD_A->getIndex();
808 // We're only going to have a second symbol in pic mode and it'll be a
809 // subtraction from the picbase. For 32-bit pic the addend is the difference
810 // between the picbase and the next address. For 32-bit static the addend
812 if (Target.getSymB()) {
813 // If this is a subtraction then we're pcrel.
814 uint32_t FixupAddress =
815 getFragmentAddress(Fragment, Layout) + Fixup.getOffset();
816 MCSymbolData *SD_B = &Asm.getSymbolData(Target.getSymB()->getSymbol());
818 FixedValue = (FixupAddress - getSymbolAddress(SD_B, Layout) +
819 Target.getConstant());
820 FixedValue += 1ULL << Log2Size;
825 // struct relocation_info (8 bytes)
826 macho::RelocationEntry MRE;
828 MRE.Word1 = ((Index << 0) |
831 (1 << 27) | // Extern
832 (macho::RIT_TLV << 28)); // Type
833 Relocations[Fragment->getParent()].push_back(MRE);
836 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
837 const MCFragment *Fragment, const MCFixup &Fixup,
838 MCValue Target, uint64_t &FixedValue) {
840 RecordX86_64Relocation(Asm, Layout, Fragment, Fixup, Target, FixedValue);
844 unsigned IsPCRel = isFixupKindPCRel(Fixup.getKind());
845 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
847 // If this is a 32-bit TLVP reloc it's handled a bit differently.
848 if (Target.getSymA() &&
849 Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP) {
850 RecordTLVPRelocation(Asm, Layout, Fragment, Fixup, Target, FixedValue);
854 // If this is a difference or a defined symbol plus an offset, then we need
855 // a scattered relocation entry.
856 // Differences always require scattered relocations.
857 if (Target.getSymB())
858 return RecordScatteredRelocation(Asm, Layout, Fragment, Fixup,
861 // Get the symbol data, if any.
862 MCSymbolData *SD = 0;
863 if (Target.getSymA())
864 SD = &Asm.getSymbolData(Target.getSymA()->getSymbol());
866 // If this is an internal relocation with an offset, it also needs a
867 // scattered relocation entry.
868 uint32_t Offset = Target.getConstant();
870 Offset += 1 << Log2Size;
871 if (Offset && SD && !doesSymbolRequireExternRelocation(SD))
872 return RecordScatteredRelocation(Asm, Layout, Fragment, Fixup,
876 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
878 unsigned IsExtern = 0;
881 if (Target.isAbsolute()) { // constant
882 // SymbolNum of 0 indicates the absolute section.
884 // FIXME: Currently, these are never generated (see code below). I cannot
885 // find a case where they are actually emitted.
886 Type = macho::RIT_Vanilla;
888 // Check whether we need an external or internal relocation.
889 if (doesSymbolRequireExternRelocation(SD)) {
891 Index = SD->getIndex();
892 // For external relocations, make sure to offset the fixup value to
893 // compensate for the addend of the symbol address, if it was
894 // undefined. This occurs with weak definitions, for example.
895 if (!SD->Symbol->isUndefined())
896 FixedValue -= getSymbolAddress(SD, Layout);
898 // The index is the section ordinal (1-based).
899 Index = SD->getFragment()->getParent()->getOrdinal() + 1;
900 FixedValue += getSectionAddress(SD->getFragment()->getParent());
903 FixedValue -= getSectionAddress(Fragment->getParent());
905 Type = macho::RIT_Vanilla;
908 // struct relocation_info (8 bytes)
909 macho::RelocationEntry MRE;
910 MRE.Word0 = FixupOffset;
911 MRE.Word1 = ((Index << 0) |
916 Relocations[Fragment->getParent()].push_back(MRE);
919 void BindIndirectSymbols(MCAssembler &Asm) {
920 // This is the point where 'as' creates actual symbols for indirect symbols
921 // (in the following two passes). It would be easier for us to do this
922 // sooner when we see the attribute, but that makes getting the order in the
923 // symbol table much more complicated than it is worth.
925 // FIXME: Revisit this when the dust settles.
927 // Bind non lazy symbol pointers first.
928 unsigned IndirectIndex = 0;
929 for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
930 ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
931 const MCSectionMachO &Section =
932 cast<MCSectionMachO>(it->SectionData->getSection());
934 if (Section.getType() != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
937 // Initialize the section indirect symbol base, if necessary.
938 if (!IndirectSymBase.count(it->SectionData))
939 IndirectSymBase[it->SectionData] = IndirectIndex;
941 Asm.getOrCreateSymbolData(*it->Symbol);
944 // Then lazy symbol pointers and symbol stubs.
946 for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
947 ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
948 const MCSectionMachO &Section =
949 cast<MCSectionMachO>(it->SectionData->getSection());
951 if (Section.getType() != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
952 Section.getType() != MCSectionMachO::S_SYMBOL_STUBS)
955 // Initialize the section indirect symbol base, if necessary.
956 if (!IndirectSymBase.count(it->SectionData))
957 IndirectSymBase[it->SectionData] = IndirectIndex;
959 // Set the symbol type to undefined lazy, but only on construction.
961 // FIXME: Do not hardcode.
963 MCSymbolData &Entry = Asm.getOrCreateSymbolData(*it->Symbol, &Created);
965 Entry.setFlags(Entry.getFlags() | 0x0001);
969 /// ComputeSymbolTable - Compute the symbol table data
971 /// \param StringTable [out] - The string table data.
972 /// \param StringIndexMap [out] - Map from symbol names to offsets in the
974 void ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
975 std::vector<MachSymbolData> &LocalSymbolData,
976 std::vector<MachSymbolData> &ExternalSymbolData,
977 std::vector<MachSymbolData> &UndefinedSymbolData) {
978 // Build section lookup table.
979 DenseMap<const MCSection*, uint8_t> SectionIndexMap;
981 for (MCAssembler::iterator it = Asm.begin(),
982 ie = Asm.end(); it != ie; ++it, ++Index)
983 SectionIndexMap[&it->getSection()] = Index;
984 assert(Index <= 256 && "Too many sections!");
986 // Index 0 is always the empty string.
987 StringMap<uint64_t> StringIndexMap;
988 StringTable += '\x00';
990 // Build the symbol arrays and the string table, but only for non-local
993 // The particular order that we collect the symbols and create the string
994 // table, then sort the symbols is chosen to match 'as'. Even though it
995 // doesn't matter for correctness, this is important for letting us diff .o
997 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
998 ie = Asm.symbol_end(); it != ie; ++it) {
999 const MCSymbol &Symbol = it->getSymbol();
1001 // Ignore non-linker visible symbols.
1002 if (!Asm.isSymbolLinkerVisible(it->getSymbol()))
1005 if (!it->isExternal() && !Symbol.isUndefined())
1008 uint64_t &Entry = StringIndexMap[Symbol.getName()];
1010 Entry = StringTable.size();
1011 StringTable += Symbol.getName();
1012 StringTable += '\x00';
1016 MSD.SymbolData = it;
1017 MSD.StringIndex = Entry;
1019 if (Symbol.isUndefined()) {
1020 MSD.SectionIndex = 0;
1021 UndefinedSymbolData.push_back(MSD);
1022 } else if (Symbol.isAbsolute()) {
1023 MSD.SectionIndex = 0;
1024 ExternalSymbolData.push_back(MSD);
1026 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
1027 assert(MSD.SectionIndex && "Invalid section index!");
1028 ExternalSymbolData.push_back(MSD);
1032 // Now add the data for local symbols.
1033 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
1034 ie = Asm.symbol_end(); it != ie; ++it) {
1035 const MCSymbol &Symbol = it->getSymbol();
1037 // Ignore non-linker visible symbols.
1038 if (!Asm.isSymbolLinkerVisible(it->getSymbol()))
1041 if (it->isExternal() || Symbol.isUndefined())
1044 uint64_t &Entry = StringIndexMap[Symbol.getName()];
1046 Entry = StringTable.size();
1047 StringTable += Symbol.getName();
1048 StringTable += '\x00';
1052 MSD.SymbolData = it;
1053 MSD.StringIndex = Entry;
1055 if (Symbol.isAbsolute()) {
1056 MSD.SectionIndex = 0;
1057 LocalSymbolData.push_back(MSD);
1059 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
1060 assert(MSD.SectionIndex && "Invalid section index!");
1061 LocalSymbolData.push_back(MSD);
1065 // External and undefined symbols are required to be in lexicographic order.
1066 std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1067 std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1069 // Set the symbol indices.
1071 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1072 LocalSymbolData[i].SymbolData->setIndex(Index++);
1073 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1074 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1075 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1076 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1078 // The string table is padded to a multiple of 4.
1079 while (StringTable.size() % 4)
1080 StringTable += '\x00';
1083 void computeSectionAddresses(const MCAssembler &Asm,
1084 const MCAsmLayout &Layout) {
1085 uint64_t StartAddress = 0;
1086 const SmallVectorImpl<MCSectionData*> &Order = Layout.getSectionOrder();
1087 for (int i = 0, n = Order.size(); i != n ; ++i) {
1088 const MCSectionData *SD = Order[i];
1089 StartAddress = RoundUpToAlignment(StartAddress, SD->getAlignment());
1090 SectionAddress[SD] = StartAddress;
1091 StartAddress += Layout.getSectionAddressSize(SD);
1092 // Explicitly pad the section to match the alignment requirements of the
1093 // following one. This is for 'gas' compatibility, it shouldn't
1094 /// strictly be necessary.
1095 StartAddress += getPaddingSize(SD, Layout);
1099 void ExecutePostLayoutBinding(MCAssembler &Asm, const MCAsmLayout &Layout) {
1100 computeSectionAddresses(Asm, Layout);
1102 // Create symbol data for any indirect symbols.
1103 BindIndirectSymbols(Asm);
1105 // Compute symbol table information and bind symbol indices.
1106 ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
1107 UndefinedSymbolData);
1111 bool IsFixupFullyResolved(const MCAssembler &Asm,
1112 const MCValue Target,
1114 const MCFragment *DF) const {
1115 // If we aren't using scattered symbols, the fixup is fully resolved.
1116 if (!Asm.getBackend().hasScatteredSymbols())
1119 // Otherwise, determine whether this value is actually resolved; scattering
1120 // may cause atoms to move.
1122 // Check if we are using the "simple" resolution algorithm (e.g.,
1124 if (!Asm.getBackend().hasReliableSymbolDifference()) {
1125 const MCSection *BaseSection = 0;
1127 BaseSection = &DF->getParent()->getSection();
1129 return isScatteredFixupFullyResolvedSimple(Asm, Target, BaseSection);
1132 // Otherwise, compute the proper answer as reliably as possible.
1134 // If this is a PCrel relocation, find the base atom (identified by its
1135 // symbol) that the fixup value is relative to.
1136 const MCSymbolData *BaseSymbol = 0;
1138 BaseSymbol = DF->getAtom();
1143 return isScatteredFixupFullyResolved(Asm, Target, BaseSymbol);
1146 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) {
1147 unsigned NumSections = Asm.size();
1149 // The section data starts after the header, the segment load command (and
1150 // section headers) and the symbol table.
1151 unsigned NumLoadCommands = 1;
1152 uint64_t LoadCommandsSize = Is64Bit ?
1153 macho::SegmentLoadCommand64Size + NumSections * macho::Section64Size :
1154 macho::SegmentLoadCommand32Size + NumSections * macho::Section32Size;
1156 // Add the symbol table load command sizes, if used.
1157 unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
1158 UndefinedSymbolData.size();
1160 NumLoadCommands += 2;
1161 LoadCommandsSize += (macho::SymtabLoadCommandSize +
1162 macho::DysymtabLoadCommandSize);
1165 // Compute the total size of the section data, as well as its file size and
1167 uint64_t SectionDataStart = (Is64Bit ? macho::Header64Size :
1168 macho::Header32Size) + LoadCommandsSize;
1169 uint64_t SectionDataSize = 0;
1170 uint64_t SectionDataFileSize = 0;
1171 uint64_t VMSize = 0;
1172 for (MCAssembler::const_iterator it = Asm.begin(),
1173 ie = Asm.end(); it != ie; ++it) {
1174 const MCSectionData &SD = *it;
1175 uint64_t Address = getSectionAddress(&SD);
1176 uint64_t Size = Layout.getSectionAddressSize(&SD);
1177 uint64_t FileSize = Layout.getSectionFileSize(&SD);
1178 FileSize += getPaddingSize(&SD, Layout);
1180 VMSize = std::max(VMSize, Address + Size);
1182 if (SD.getSection().isVirtualSection())
1185 SectionDataSize = std::max(SectionDataSize, Address + Size);
1186 SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
1189 // The section data is padded to 4 bytes.
1191 // FIXME: Is this machine dependent?
1192 unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
1193 SectionDataFileSize += SectionDataPadding;
1195 // Write the prolog, starting with the header and load command...
1196 WriteHeader(NumLoadCommands, LoadCommandsSize,
1197 Asm.getSubsectionsViaSymbols());
1198 WriteSegmentLoadCommand(NumSections, VMSize,
1199 SectionDataStart, SectionDataSize);
1201 // ... and then the section headers.
1202 uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
1203 for (MCAssembler::const_iterator it = Asm.begin(),
1204 ie = Asm.end(); it != ie; ++it) {
1205 std::vector<macho::RelocationEntry> &Relocs = Relocations[it];
1206 unsigned NumRelocs = Relocs.size();
1207 uint64_t SectionStart = SectionDataStart + getSectionAddress(it);
1208 WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
1209 RelocTableEnd += NumRelocs * macho::RelocationInfoSize;
1212 // Write the symbol table load command, if used.
1214 unsigned FirstLocalSymbol = 0;
1215 unsigned NumLocalSymbols = LocalSymbolData.size();
1216 unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
1217 unsigned NumExternalSymbols = ExternalSymbolData.size();
1218 unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
1219 unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
1220 unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
1221 unsigned NumSymTabSymbols =
1222 NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
1223 uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
1224 uint64_t IndirectSymbolOffset = 0;
1226 // If used, the indirect symbols are written after the section data.
1227 if (NumIndirectSymbols)
1228 IndirectSymbolOffset = RelocTableEnd;
1230 // The symbol table is written after the indirect symbol data.
1231 uint64_t SymbolTableOffset = RelocTableEnd + IndirectSymbolSize;
1233 // The string table is written after symbol table.
1234 uint64_t StringTableOffset =
1235 SymbolTableOffset + NumSymTabSymbols * (Is64Bit ? macho::Nlist64Size :
1236 macho::Nlist32Size);
1237 WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
1238 StringTableOffset, StringTable.size());
1240 WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
1241 FirstExternalSymbol, NumExternalSymbols,
1242 FirstUndefinedSymbol, NumUndefinedSymbols,
1243 IndirectSymbolOffset, NumIndirectSymbols);
1246 // Write the actual section data.
1247 for (MCAssembler::const_iterator it = Asm.begin(),
1248 ie = Asm.end(); it != ie; ++it) {
1249 Asm.WriteSectionData(it, Layout, this);
1251 uint64_t Pad = getPaddingSize(it, Layout);
1252 for (unsigned int i = 0; i < Pad; ++i)
1256 // Write the extra padding.
1257 WriteZeros(SectionDataPadding);
1259 // Write the relocation entries.
1260 for (MCAssembler::const_iterator it = Asm.begin(),
1261 ie = Asm.end(); it != ie; ++it) {
1262 // Write the section relocation entries, in reverse order to match 'as'
1263 // (approximately, the exact algorithm is more complicated than this).
1264 std::vector<macho::RelocationEntry> &Relocs = Relocations[it];
1265 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1266 Write32(Relocs[e - i - 1].Word0);
1267 Write32(Relocs[e - i - 1].Word1);
1271 // Write the symbol table data, if used.
1273 // Write the indirect symbol entries.
1274 for (MCAssembler::const_indirect_symbol_iterator
1275 it = Asm.indirect_symbol_begin(),
1276 ie = Asm.indirect_symbol_end(); it != ie; ++it) {
1277 // Indirect symbols in the non lazy symbol pointer section have some
1278 // special handling.
1279 const MCSectionMachO &Section =
1280 static_cast<const MCSectionMachO&>(it->SectionData->getSection());
1281 if (Section.getType() == MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS) {
1282 // If this symbol is defined and internal, mark it as such.
1283 if (it->Symbol->isDefined() &&
1284 !Asm.getSymbolData(*it->Symbol).isExternal()) {
1285 uint32_t Flags = macho::ISF_Local;
1286 if (it->Symbol->isAbsolute())
1287 Flags |= macho::ISF_Absolute;
1293 Write32(Asm.getSymbolData(*it->Symbol).getIndex());
1296 // FIXME: Check that offsets match computed ones.
1298 // Write the symbol table entries.
1299 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1300 WriteNlist(LocalSymbolData[i], Layout);
1301 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1302 WriteNlist(ExternalSymbolData[i], Layout);
1303 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1304 WriteNlist(UndefinedSymbolData[i], Layout);
1306 // Write the string table.
1307 OS << StringTable.str();
1314 MCObjectWriter *llvm::createMachObjectWriter(raw_ostream &OS, bool is64Bit,
1316 uint32_t CPUSubtype,
1317 bool IsLittleEndian) {
1318 return new MachObjectWriter(OS, is64Bit, CPUType, CPUSubtype, IsLittleEndian);