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/MC/MachObjectWriter.h"
11 #include "llvm/ADT/StringMap.h"
12 #include "llvm/ADT/Twine.h"
13 #include "llvm/MC/MCAssembler.h"
14 #include "llvm/MC/MCAsmLayout.h"
15 #include "llvm/MC/MCExpr.h"
16 #include "llvm/MC/MCObjectWriter.h"
17 #include "llvm/MC/MCSectionMachO.h"
18 #include "llvm/MC/MCSymbol.h"
19 #include "llvm/MC/MCMachOSymbolFlags.h"
20 #include "llvm/MC/MCValue.h"
21 #include "llvm/Support/ErrorHandling.h"
22 #include "llvm/Support/MachO.h"
23 #include "llvm/Target/TargetAsmBackend.h"
26 #include "../Target/X86/X86FixupKinds.h"
31 static unsigned getFixupKindLog2Size(unsigned Kind) {
33 default: llvm_unreachable("invalid fixup kind!");
34 case X86::reloc_pcrel_1byte:
35 case FK_Data_1: return 0;
36 case FK_Data_2: return 1;
37 case X86::reloc_pcrel_4byte:
38 case X86::reloc_riprel_4byte:
39 case X86::reloc_riprel_4byte_movq_load:
40 case FK_Data_4: return 2;
41 case FK_Data_8: return 3;
45 static bool isFixupKindPCRel(unsigned Kind) {
49 case X86::reloc_pcrel_1byte:
50 case X86::reloc_pcrel_4byte:
51 case X86::reloc_riprel_4byte:
52 case X86::reloc_riprel_4byte_movq_load:
57 static bool isFixupKindRIPRel(unsigned Kind) {
58 return Kind == X86::reloc_riprel_4byte ||
59 Kind == X86::reloc_riprel_4byte_movq_load;
62 static bool doesSymbolRequireExternRelocation(MCSymbolData *SD) {
63 // Undefined symbols are always extern.
64 if (SD->Symbol->isUndefined())
67 // References to weak definitions require external relocation entries; the
68 // definition may not always be the one in the same object file.
69 if (SD->getFlags() & SF_WeakDefinition)
72 // Otherwise, we can use an internal relocation.
78 class MachObjectWriterImpl {
79 // See <mach-o/loader.h>.
81 Header_Magic32 = 0xFEEDFACE,
82 Header_Magic64 = 0xFEEDFACF
88 SegmentLoadCommand32Size = 56,
89 SegmentLoadCommand64Size = 72,
92 SymtabLoadCommandSize = 24,
93 DysymtabLoadCommandSize = 80,
96 RelocationInfoSize = 8
104 HF_SubsectionsViaSymbols = 0x2000
107 enum LoadCommandType {
114 // See <mach-o/nlist.h>.
115 enum SymbolTypeType {
116 STT_Undefined = 0x00,
121 enum SymbolTypeFlags {
122 // If any of these bits are set, then the entry is a stab entry number (see
123 // <mach-o/stab.h>. Otherwise the other masks apply.
124 STF_StabsEntryMask = 0xe0,
128 STF_PrivateExtern = 0x10
131 /// IndirectSymbolFlags - Flags for encoding special values in the indirect
133 enum IndirectSymbolFlags {
134 ISF_Local = 0x80000000,
135 ISF_Absolute = 0x40000000
138 /// RelocationFlags - Special flags for addresses.
139 enum RelocationFlags {
140 RF_Scattered = 0x80000000
143 enum RelocationInfoType {
147 RIT_PreboundLazyPointer = 3,
148 RIT_LocalDifference = 4
151 /// X86_64 uses its own relocation types.
152 enum RelocationInfoTypeX86_64 {
153 RIT_X86_64_Unsigned = 0,
154 RIT_X86_64_Signed = 1,
155 RIT_X86_64_Branch = 2,
156 RIT_X86_64_GOTLoad = 3,
158 RIT_X86_64_Subtractor = 5,
159 RIT_X86_64_Signed1 = 6,
160 RIT_X86_64_Signed2 = 7,
161 RIT_X86_64_Signed4 = 8
164 /// MachSymbolData - Helper struct for containing some precomputed information
166 struct MachSymbolData {
167 MCSymbolData *SymbolData;
168 uint64_t StringIndex;
169 uint8_t SectionIndex;
171 // Support lexicographic sorting.
172 bool operator<(const MachSymbolData &RHS) const {
173 const std::string &Name = SymbolData->getSymbol().getName();
174 return Name < RHS.SymbolData->getSymbol().getName();
178 /// @name Relocation Data
181 struct MachRelocationEntry {
186 llvm::DenseMap<const MCSectionData*,
187 std::vector<MachRelocationEntry> > Relocations;
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 MachObjectWriter *Writer;
204 unsigned Is64Bit : 1;
207 MachObjectWriterImpl(MachObjectWriter *_Writer, bool _Is64Bit)
208 : Writer(_Writer), OS(Writer->getStream()), Is64Bit(_Is64Bit) {
211 void Write8(uint8_t Value) { Writer->Write8(Value); }
212 void Write16(uint16_t Value) { Writer->Write16(Value); }
213 void Write32(uint32_t Value) { Writer->Write32(Value); }
214 void Write64(uint64_t Value) { Writer->Write64(Value); }
215 void WriteZeros(unsigned N) { Writer->WriteZeros(N); }
216 void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
217 Writer->WriteBytes(Str, ZeroFillSize);
220 void WriteHeader(unsigned NumLoadCommands, unsigned LoadCommandsSize,
221 bool SubsectionsViaSymbols) {
224 if (SubsectionsViaSymbols)
225 Flags |= HF_SubsectionsViaSymbols;
227 // struct mach_header (28 bytes) or
228 // struct mach_header_64 (32 bytes)
230 uint64_t Start = OS.tell();
233 Write32(Is64Bit ? Header_Magic64 : Header_Magic32);
235 // FIXME: Support cputype.
236 Write32(Is64Bit ? MachO::CPUTypeX86_64 : MachO::CPUTypeI386);
237 // FIXME: Support cpusubtype.
238 Write32(MachO::CPUSubType_I386_ALL);
240 Write32(NumLoadCommands); // Object files have a single load command, the
242 Write32(LoadCommandsSize);
245 Write32(0); // reserved
247 assert(OS.tell() - Start == Is64Bit ? Header64Size : Header32Size);
250 /// WriteSegmentLoadCommand - Write a segment load command.
252 /// \arg NumSections - The number of sections in this segment.
253 /// \arg SectionDataSize - The total size of the sections.
254 void WriteSegmentLoadCommand(unsigned NumSections,
256 uint64_t SectionDataStartOffset,
257 uint64_t SectionDataSize) {
258 // struct segment_command (56 bytes) or
259 // struct segment_command_64 (72 bytes)
261 uint64_t Start = OS.tell();
264 unsigned SegmentLoadCommandSize = Is64Bit ? SegmentLoadCommand64Size :
265 SegmentLoadCommand32Size;
266 Write32(Is64Bit ? LCT_Segment64 : LCT_Segment);
267 Write32(SegmentLoadCommandSize +
268 NumSections * (Is64Bit ? Section64Size : Section32Size));
272 Write64(0); // vmaddr
273 Write64(VMSize); // vmsize
274 Write64(SectionDataStartOffset); // file offset
275 Write64(SectionDataSize); // file size
277 Write32(0); // vmaddr
278 Write32(VMSize); // vmsize
279 Write32(SectionDataStartOffset); // file offset
280 Write32(SectionDataSize); // file size
282 Write32(0x7); // maxprot
283 Write32(0x7); // initprot
284 Write32(NumSections);
287 assert(OS.tell() - Start == SegmentLoadCommandSize);
290 void WriteSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
291 const MCSectionData &SD, uint64_t FileOffset,
292 uint64_t RelocationsStart, unsigned NumRelocations) {
293 uint64_t SectionSize = Layout.getSectionSize(&SD);
295 // The offset is unused for virtual sections.
296 if (Asm.getBackend().isVirtualSection(SD.getSection())) {
297 assert(Layout.getSectionFileSize(&SD) == 0 && "Invalid file size!");
301 // struct section (68 bytes) or
302 // struct section_64 (80 bytes)
304 uint64_t Start = OS.tell();
307 // FIXME: cast<> support!
308 const MCSectionMachO &Section =
309 static_cast<const MCSectionMachO&>(SD.getSection());
310 WriteBytes(Section.getSectionName(), 16);
311 WriteBytes(Section.getSegmentName(), 16);
313 Write64(Layout.getSectionAddress(&SD)); // address
314 Write64(SectionSize); // size
316 Write32(Layout.getSectionAddress(&SD)); // address
317 Write32(SectionSize); // size
321 unsigned Flags = Section.getTypeAndAttributes();
322 if (SD.hasInstructions())
323 Flags |= MCSectionMachO::S_ATTR_SOME_INSTRUCTIONS;
325 assert(isPowerOf2_32(SD.getAlignment()) && "Invalid alignment!");
326 Write32(Log2_32(SD.getAlignment()));
327 Write32(NumRelocations ? RelocationsStart : 0);
328 Write32(NumRelocations);
330 Write32(0); // reserved1
331 Write32(Section.getStubSize()); // reserved2
333 Write32(0); // reserved3
335 assert(OS.tell() - Start == Is64Bit ? Section64Size : Section32Size);
338 void WriteSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
339 uint32_t StringTableOffset,
340 uint32_t StringTableSize) {
341 // struct symtab_command (24 bytes)
343 uint64_t Start = OS.tell();
347 Write32(SymtabLoadCommandSize);
348 Write32(SymbolOffset);
350 Write32(StringTableOffset);
351 Write32(StringTableSize);
353 assert(OS.tell() - Start == SymtabLoadCommandSize);
356 void WriteDysymtabLoadCommand(uint32_t FirstLocalSymbol,
357 uint32_t NumLocalSymbols,
358 uint32_t FirstExternalSymbol,
359 uint32_t NumExternalSymbols,
360 uint32_t FirstUndefinedSymbol,
361 uint32_t NumUndefinedSymbols,
362 uint32_t IndirectSymbolOffset,
363 uint32_t NumIndirectSymbols) {
364 // struct dysymtab_command (80 bytes)
366 uint64_t Start = OS.tell();
369 Write32(LCT_Dysymtab);
370 Write32(DysymtabLoadCommandSize);
371 Write32(FirstLocalSymbol);
372 Write32(NumLocalSymbols);
373 Write32(FirstExternalSymbol);
374 Write32(NumExternalSymbols);
375 Write32(FirstUndefinedSymbol);
376 Write32(NumUndefinedSymbols);
377 Write32(0); // tocoff
379 Write32(0); // modtaboff
380 Write32(0); // nmodtab
381 Write32(0); // extrefsymoff
382 Write32(0); // nextrefsyms
383 Write32(IndirectSymbolOffset);
384 Write32(NumIndirectSymbols);
385 Write32(0); // extreloff
386 Write32(0); // nextrel
387 Write32(0); // locreloff
388 Write32(0); // nlocrel
390 assert(OS.tell() - Start == DysymtabLoadCommandSize);
393 void WriteNlist(MachSymbolData &MSD, const MCAsmLayout &Layout) {
394 MCSymbolData &Data = *MSD.SymbolData;
395 const MCSymbol &Symbol = Data.getSymbol();
397 uint16_t Flags = Data.getFlags();
398 uint32_t Address = 0;
400 // Set the N_TYPE bits. See <mach-o/nlist.h>.
402 // FIXME: Are the prebound or indirect fields possible here?
403 if (Symbol.isUndefined())
404 Type = STT_Undefined;
405 else if (Symbol.isAbsolute())
410 // FIXME: Set STAB bits.
412 if (Data.isPrivateExtern())
413 Type |= STF_PrivateExtern;
416 if (Data.isExternal() || Symbol.isUndefined())
417 Type |= STF_External;
419 // Compute the symbol address.
420 if (Symbol.isDefined()) {
421 if (Symbol.isAbsolute()) {
422 Address = cast<MCConstantExpr>(Symbol.getVariableValue())->getValue();
424 Address = Layout.getSymbolAddress(&Data);
426 } else if (Data.isCommon()) {
427 // Common symbols are encoded with the size in the address
428 // field, and their alignment in the flags.
429 Address = Data.getCommonSize();
431 // Common alignment is packed into the 'desc' bits.
432 if (unsigned Align = Data.getCommonAlignment()) {
433 unsigned Log2Size = Log2_32(Align);
434 assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
436 report_fatal_error("invalid 'common' alignment '" +
438 // FIXME: Keep this mask with the SymbolFlags enumeration.
439 Flags = (Flags & 0xF0FF) | (Log2Size << 8);
443 // struct nlist (12 bytes)
445 Write32(MSD.StringIndex);
447 Write8(MSD.SectionIndex);
449 // The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
458 // FIXME: We really need to improve the relocation validation. Basically, we
459 // want to implement a separate computation which evaluates the relocation
460 // entry as the linker would, and verifies that the resultant fixup value is
461 // exactly what the encoder wanted. This will catch several classes of
464 // - Relocation entry bugs, the two algorithms are unlikely to have the same
467 // - Relaxation issues, where we forget to relax something.
469 // - Input errors, where something cannot be correctly encoded. 'as' allows
470 // these through in many cases.
472 void RecordX86_64Relocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
473 const MCFragment *Fragment,
474 const MCAsmFixup &Fixup, MCValue Target,
475 uint64_t &FixedValue) {
476 unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
477 unsigned IsRIPRel = isFixupKindRIPRel(Fixup.Kind);
478 unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
481 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.Offset;
484 unsigned IsExtern = 0;
487 Value = Target.getConstant();
490 // Compensate for the relocation offset, Darwin x86_64 relocations only
491 // have the addend and appear to have attempted to define it to be the
492 // actual expression addend without the PCrel bias. However, instructions
493 // with data following the relocation are not accomodated for (see comment
494 // below regarding SIGNED{1,2,4}), so it isn't exactly that either.
495 Value += 1LL << Log2Size;
498 if (Target.isAbsolute()) { // constant
499 // SymbolNum of 0 indicates the absolute section.
500 Type = RIT_X86_64_Unsigned;
503 // FIXME: I believe this is broken, I don't think the linker can
504 // understand it. I think it would require a local relocation, but I'm not
505 // sure if that would work either. The official way to get an absolute
506 // PCrel relocation is to use an absolute symbol (which we don't support
510 Type = RIT_X86_64_Branch;
512 } else if (Target.getSymB()) { // A - B + constant
513 const MCSymbol *A = &Target.getSymA()->getSymbol();
514 MCSymbolData &A_SD = Asm.getSymbolData(*A);
515 const MCSymbolData *A_Base = Asm.getAtom(Layout, &A_SD);
517 const MCSymbol *B = &Target.getSymB()->getSymbol();
518 MCSymbolData &B_SD = Asm.getSymbolData(*B);
519 const MCSymbolData *B_Base = Asm.getAtom(Layout, &B_SD);
521 // Neither symbol can be modified.
522 if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
523 Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
524 report_fatal_error("unsupported relocation of modified symbol");
526 // We don't support PCrel relocations of differences. Darwin 'as' doesn't
527 // implement most of these correctly.
529 report_fatal_error("unsupported pc-relative relocation of difference");
531 // We don't currently support any situation where one or both of the
532 // symbols would require a local relocation. This is almost certainly
533 // unused and may not be possible to encode correctly.
534 if (!A_Base || !B_Base)
535 report_fatal_error("unsupported local relocations in difference");
537 // Darwin 'as' doesn't emit correct relocations for this (it ends up with
538 // a single SIGNED relocation); reject it for now.
539 if (A_Base == B_Base)
540 report_fatal_error("unsupported relocation with identical base");
542 Value += Layout.getSymbolAddress(&A_SD) - Layout.getSymbolAddress(A_Base);
543 Value -= Layout.getSymbolAddress(&B_SD) - Layout.getSymbolAddress(B_Base);
545 Index = A_Base->getIndex();
547 Type = RIT_X86_64_Unsigned;
549 MachRelocationEntry MRE;
550 MRE.Word0 = FixupOffset;
551 MRE.Word1 = ((Index << 0) |
556 Relocations[Fragment->getParent()].push_back(MRE);
558 Index = B_Base->getIndex();
560 Type = RIT_X86_64_Subtractor;
562 const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
563 MCSymbolData &SD = Asm.getSymbolData(*Symbol);
564 const MCSymbolData *Base = Asm.getAtom(Layout, &SD);
566 // Relocations inside debug sections always use local relocations when
567 // possible. This seems to be done because the debugger doesn't fully
568 // understand x86_64 relocation entries, and expects to find values that
569 // have already been fixed up.
570 if (Symbol->isInSection()) {
571 const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
572 Fragment->getParent()->getSection());
573 if (Section.hasAttribute(MCSectionMachO::S_ATTR_DEBUG))
577 // x86_64 almost always uses external relocations, except when there is no
578 // symbol to use as a base address (a local symbol with no preceeding
579 // non-local symbol).
581 Index = Base->getIndex();
584 // Add the local offset, if needed.
586 Value += Layout.getSymbolAddress(&SD) - Layout.getSymbolAddress(Base);
587 } else if (Symbol->isInSection()) {
588 // The index is the section ordinal (1-based).
589 Index = SD.getFragment()->getParent()->getOrdinal() + 1;
591 Value += Layout.getSymbolAddress(&SD);
594 Value -= FixupOffset + (1 << Log2Size);
596 report_fatal_error("unsupported relocation of undefined symbol '" +
597 Symbol->getName() + "'");
600 MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
603 if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
604 // x86_64 distinguishes movq foo@GOTPCREL so that the linker can
605 // rewrite the movq to an leaq at link time if the symbol ends up in
606 // the same linkage unit.
607 if (unsigned(Fixup.Kind) == X86::reloc_riprel_4byte_movq_load)
608 Type = RIT_X86_64_GOTLoad;
610 Type = RIT_X86_64_GOT;
611 } else if (Modifier != MCSymbolRefExpr::VK_None)
612 report_fatal_error("unsupported symbol modifier in relocation");
614 Type = RIT_X86_64_Signed;
616 if (Modifier != MCSymbolRefExpr::VK_None)
617 report_fatal_error("unsupported symbol modifier in branch "
620 Type = RIT_X86_64_Branch;
623 // The Darwin x86_64 relocation format has a problem where it cannot
624 // encode an address (L<foo> + <constant>) which is outside the atom
625 // containing L<foo>. Generally, this shouldn't occur but it does happen
626 // when we have a RIPrel instruction with data following the relocation
627 // entry (e.g., movb $012, L0(%rip)). Even with the PCrel adjustment
628 // Darwin x86_64 uses, the offset is still negative and the linker has
629 // no way to recognize this.
631 // To work around this, Darwin uses several special relocation types to
632 // indicate the offsets. However, the specification or implementation of
633 // these seems to also be incomplete; they should adjust the addend as
634 // well based on the actual encoded instruction (the additional bias),
635 // but instead appear to just look at the final offset.
637 switch (-(Target.getConstant() + (1LL << Log2Size))) {
638 case 1: Type = RIT_X86_64_Signed1; break;
639 case 2: Type = RIT_X86_64_Signed2; break;
640 case 4: Type = RIT_X86_64_Signed4; break;
644 if (Modifier == MCSymbolRefExpr::VK_GOT) {
645 Type = RIT_X86_64_GOT;
646 } else if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
647 // GOTPCREL is allowed as a modifier on non-PCrel instructions, in
648 // which case all we do is set the PCrel bit in the relocation entry;
649 // this is used with exception handling, for example. The source is
650 // required to include any necessary offset directly.
651 Type = RIT_X86_64_GOT;
653 } else if (Modifier != MCSymbolRefExpr::VK_None)
654 report_fatal_error("unsupported symbol modifier in relocation");
656 Type = RIT_X86_64_Unsigned;
660 // x86_64 always writes custom values into the fixups.
663 // struct relocation_info (8 bytes)
664 MachRelocationEntry MRE;
665 MRE.Word0 = FixupOffset;
666 MRE.Word1 = ((Index << 0) |
671 Relocations[Fragment->getParent()].push_back(MRE);
674 void RecordScatteredRelocation(const MCAssembler &Asm,
675 const MCAsmLayout &Layout,
676 const MCFragment *Fragment,
677 const MCAsmFixup &Fixup, MCValue Target,
678 uint64_t &FixedValue) {
679 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.Offset;
680 unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
681 unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
682 unsigned Type = RIT_Vanilla;
685 const MCSymbol *A = &Target.getSymA()->getSymbol();
686 MCSymbolData *A_SD = &Asm.getSymbolData(*A);
688 if (!A_SD->getFragment())
689 report_fatal_error("symbol '" + A->getName() +
690 "' can not be undefined in a subtraction expression");
692 uint32_t Value = Layout.getSymbolAddress(A_SD);
695 if (const MCSymbolRefExpr *B = Target.getSymB()) {
696 MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
698 if (!B_SD->getFragment())
699 report_fatal_error("symbol '" + B->getSymbol().getName() +
700 "' can not be undefined in a subtraction expression");
702 // Select the appropriate difference relocation type.
704 // Note that there is no longer any semantic difference between these two
705 // relocation types from the linkers point of view, this is done solely
706 // for pedantic compatibility with 'as'.
707 Type = A_SD->isExternal() ? RIT_Difference : RIT_LocalDifference;
708 Value2 = Layout.getSymbolAddress(B_SD);
711 // Relocations are written out in reverse order, so the PAIR comes first.
712 if (Type == RIT_Difference || Type == RIT_LocalDifference) {
713 MachRelocationEntry MRE;
714 MRE.Word0 = ((0 << 0) |
720 Relocations[Fragment->getParent()].push_back(MRE);
723 MachRelocationEntry MRE;
724 MRE.Word0 = ((FixupOffset << 0) |
730 Relocations[Fragment->getParent()].push_back(MRE);
733 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
734 const MCFragment *Fragment, const MCAsmFixup &Fixup,
735 MCValue Target, uint64_t &FixedValue) {
737 RecordX86_64Relocation(Asm, Layout, Fragment, Fixup, Target, FixedValue);
741 unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
742 unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
744 // If this is a difference or a defined symbol plus an offset, then we need
745 // a scattered relocation entry.
746 // Differences always require scattered relocations.
747 if (Target.getSymB())
748 return RecordScatteredRelocation(Asm, Layout, Fragment, Fixup,
751 // Get the symbol data, if any.
752 MCSymbolData *SD = 0;
753 if (Target.getSymA())
754 SD = &Asm.getSymbolData(Target.getSymA()->getSymbol());
756 // If this is an internal relocation with an offset, it also needs a
757 // scattered relocation entry.
758 uint32_t Offset = Target.getConstant();
760 Offset += 1 << Log2Size;
761 if (Offset && SD && !doesSymbolRequireExternRelocation(SD))
762 return RecordScatteredRelocation(Asm, Layout, Fragment, Fixup,
766 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.Offset;
769 unsigned IsExtern = 0;
772 if (Target.isAbsolute()) { // constant
773 // SymbolNum of 0 indicates the absolute section.
775 // FIXME: Currently, these are never generated (see code below). I cannot
776 // find a case where they are actually emitted.
780 // Check whether we need an external or internal relocation.
781 if (doesSymbolRequireExternRelocation(SD)) {
783 Index = SD->getIndex();
784 // For external relocations, make sure to offset the fixup value to
785 // compensate for the addend of the symbol address, if it was
786 // undefined. This occurs with weak definitions, for example.
787 if (!SD->Symbol->isUndefined())
788 FixedValue -= Layout.getSymbolAddress(SD);
791 // The index is the section ordinal (1-based).
792 Index = SD->getFragment()->getParent()->getOrdinal() + 1;
793 Value = Layout.getSymbolAddress(SD);
799 // struct relocation_info (8 bytes)
800 MachRelocationEntry MRE;
801 MRE.Word0 = FixupOffset;
802 MRE.Word1 = ((Index << 0) |
807 Relocations[Fragment->getParent()].push_back(MRE);
810 void BindIndirectSymbols(MCAssembler &Asm) {
811 // This is the point where 'as' creates actual symbols for indirect symbols
812 // (in the following two passes). It would be easier for us to do this
813 // sooner when we see the attribute, but that makes getting the order in the
814 // symbol table much more complicated than it is worth.
816 // FIXME: Revisit this when the dust settles.
818 // Bind non lazy symbol pointers first.
819 for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
820 ie = Asm.indirect_symbol_end(); it != ie; ++it) {
821 // FIXME: cast<> support!
822 const MCSectionMachO &Section =
823 static_cast<const MCSectionMachO&>(it->SectionData->getSection());
825 if (Section.getType() != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
828 Asm.getOrCreateSymbolData(*it->Symbol);
831 // Then lazy symbol pointers and symbol stubs.
832 for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
833 ie = Asm.indirect_symbol_end(); it != ie; ++it) {
834 // FIXME: cast<> support!
835 const MCSectionMachO &Section =
836 static_cast<const MCSectionMachO&>(it->SectionData->getSection());
838 if (Section.getType() != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
839 Section.getType() != MCSectionMachO::S_SYMBOL_STUBS)
842 // Set the symbol type to undefined lazy, but only on construction.
844 // FIXME: Do not hardcode.
846 MCSymbolData &Entry = Asm.getOrCreateSymbolData(*it->Symbol, &Created);
848 Entry.setFlags(Entry.getFlags() | 0x0001);
852 /// ComputeSymbolTable - Compute the symbol table data
854 /// \param StringTable [out] - The string table data.
855 /// \param StringIndexMap [out] - Map from symbol names to offsets in the
857 void ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
858 std::vector<MachSymbolData> &LocalSymbolData,
859 std::vector<MachSymbolData> &ExternalSymbolData,
860 std::vector<MachSymbolData> &UndefinedSymbolData) {
861 // Build section lookup table.
862 DenseMap<const MCSection*, uint8_t> SectionIndexMap;
864 for (MCAssembler::iterator it = Asm.begin(),
865 ie = Asm.end(); it != ie; ++it, ++Index)
866 SectionIndexMap[&it->getSection()] = Index;
867 assert(Index <= 256 && "Too many sections!");
869 // Index 0 is always the empty string.
870 StringMap<uint64_t> StringIndexMap;
871 StringTable += '\x00';
873 // Build the symbol arrays and the string table, but only for non-local
876 // The particular order that we collect the symbols and create the string
877 // table, then sort the symbols is chosen to match 'as'. Even though it
878 // doesn't matter for correctness, this is important for letting us diff .o
880 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
881 ie = Asm.symbol_end(); it != ie; ++it) {
882 const MCSymbol &Symbol = it->getSymbol();
884 // Ignore non-linker visible symbols.
885 if (!Asm.isSymbolLinkerVisible(it))
888 if (!it->isExternal() && !Symbol.isUndefined())
891 uint64_t &Entry = StringIndexMap[Symbol.getName()];
893 Entry = StringTable.size();
894 StringTable += Symbol.getName();
895 StringTable += '\x00';
900 MSD.StringIndex = Entry;
902 if (Symbol.isUndefined()) {
903 MSD.SectionIndex = 0;
904 UndefinedSymbolData.push_back(MSD);
905 } else if (Symbol.isAbsolute()) {
906 MSD.SectionIndex = 0;
907 ExternalSymbolData.push_back(MSD);
909 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
910 assert(MSD.SectionIndex && "Invalid section index!");
911 ExternalSymbolData.push_back(MSD);
915 // Now add the data for local symbols.
916 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
917 ie = Asm.symbol_end(); it != ie; ++it) {
918 const MCSymbol &Symbol = it->getSymbol();
920 // Ignore non-linker visible symbols.
921 if (!Asm.isSymbolLinkerVisible(it))
924 if (it->isExternal() || Symbol.isUndefined())
927 uint64_t &Entry = StringIndexMap[Symbol.getName()];
929 Entry = StringTable.size();
930 StringTable += Symbol.getName();
931 StringTable += '\x00';
936 MSD.StringIndex = Entry;
938 if (Symbol.isAbsolute()) {
939 MSD.SectionIndex = 0;
940 LocalSymbolData.push_back(MSD);
942 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
943 assert(MSD.SectionIndex && "Invalid section index!");
944 LocalSymbolData.push_back(MSD);
948 // External and undefined symbols are required to be in lexicographic order.
949 std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
950 std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
952 // Set the symbol indices.
954 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
955 LocalSymbolData[i].SymbolData->setIndex(Index++);
956 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
957 ExternalSymbolData[i].SymbolData->setIndex(Index++);
958 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
959 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
961 // The string table is padded to a multiple of 4.
962 while (StringTable.size() % 4)
963 StringTable += '\x00';
966 void ExecutePostLayoutBinding(MCAssembler &Asm) {
967 // Create symbol data for any indirect symbols.
968 BindIndirectSymbols(Asm);
970 // Compute symbol table information and bind symbol indices.
971 ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
972 UndefinedSymbolData);
975 void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout) {
976 unsigned NumSections = Asm.size();
978 // The section data starts after the header, the segment load command (and
979 // section headers) and the symbol table.
980 unsigned NumLoadCommands = 1;
981 uint64_t LoadCommandsSize = Is64Bit ?
982 SegmentLoadCommand64Size + NumSections * Section64Size :
983 SegmentLoadCommand32Size + NumSections * Section32Size;
985 // Add the symbol table load command sizes, if used.
986 unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
987 UndefinedSymbolData.size();
989 NumLoadCommands += 2;
990 LoadCommandsSize += SymtabLoadCommandSize + DysymtabLoadCommandSize;
993 // Compute the total size of the section data, as well as its file size and
995 uint64_t SectionDataStart = (Is64Bit ? Header64Size : Header32Size)
997 uint64_t SectionDataSize = 0;
998 uint64_t SectionDataFileSize = 0;
1000 for (MCAssembler::const_iterator it = Asm.begin(),
1001 ie = Asm.end(); it != ie; ++it) {
1002 const MCSectionData &SD = *it;
1003 uint64_t Address = Layout.getSectionAddress(&SD);
1004 uint64_t Size = Layout.getSectionSize(&SD);
1005 uint64_t FileSize = Layout.getSectionFileSize(&SD);
1007 VMSize = std::max(VMSize, Address + Size);
1009 if (Asm.getBackend().isVirtualSection(SD.getSection()))
1012 SectionDataSize = std::max(SectionDataSize, Address + Size);
1013 SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
1016 // The section data is padded to 4 bytes.
1018 // FIXME: Is this machine dependent?
1019 unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
1020 SectionDataFileSize += SectionDataPadding;
1022 // Write the prolog, starting with the header and load command...
1023 WriteHeader(NumLoadCommands, LoadCommandsSize,
1024 Asm.getSubsectionsViaSymbols());
1025 WriteSegmentLoadCommand(NumSections, VMSize,
1026 SectionDataStart, SectionDataSize);
1028 // ... and then the section headers.
1029 uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
1030 for (MCAssembler::const_iterator it = Asm.begin(),
1031 ie = Asm.end(); it != ie; ++it) {
1032 std::vector<MachRelocationEntry> &Relocs = Relocations[it];
1033 unsigned NumRelocs = Relocs.size();
1034 uint64_t SectionStart = SectionDataStart + Layout.getSectionAddress(it);
1035 WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
1036 RelocTableEnd += NumRelocs * RelocationInfoSize;
1039 // Write the symbol table load command, if used.
1041 unsigned FirstLocalSymbol = 0;
1042 unsigned NumLocalSymbols = LocalSymbolData.size();
1043 unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
1044 unsigned NumExternalSymbols = ExternalSymbolData.size();
1045 unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
1046 unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
1047 unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
1048 unsigned NumSymTabSymbols =
1049 NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
1050 uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
1051 uint64_t IndirectSymbolOffset = 0;
1053 // If used, the indirect symbols are written after the section data.
1054 if (NumIndirectSymbols)
1055 IndirectSymbolOffset = RelocTableEnd;
1057 // The symbol table is written after the indirect symbol data.
1058 uint64_t SymbolTableOffset = RelocTableEnd + IndirectSymbolSize;
1060 // The string table is written after symbol table.
1061 uint64_t StringTableOffset =
1062 SymbolTableOffset + NumSymTabSymbols * (Is64Bit ? Nlist64Size :
1064 WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
1065 StringTableOffset, StringTable.size());
1067 WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
1068 FirstExternalSymbol, NumExternalSymbols,
1069 FirstUndefinedSymbol, NumUndefinedSymbols,
1070 IndirectSymbolOffset, NumIndirectSymbols);
1073 // Write the actual section data.
1074 for (MCAssembler::const_iterator it = Asm.begin(),
1075 ie = Asm.end(); it != ie; ++it)
1076 Asm.WriteSectionData(it, Layout, Writer);
1078 // Write the extra padding.
1079 WriteZeros(SectionDataPadding);
1081 // Write the relocation entries.
1082 for (MCAssembler::const_iterator it = Asm.begin(),
1083 ie = Asm.end(); it != ie; ++it) {
1084 // Write the section relocation entries, in reverse order to match 'as'
1085 // (approximately, the exact algorithm is more complicated than this).
1086 std::vector<MachRelocationEntry> &Relocs = Relocations[it];
1087 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1088 Write32(Relocs[e - i - 1].Word0);
1089 Write32(Relocs[e - i - 1].Word1);
1093 // Write the symbol table data, if used.
1095 // Write the indirect symbol entries.
1096 for (MCAssembler::const_indirect_symbol_iterator
1097 it = Asm.indirect_symbol_begin(),
1098 ie = Asm.indirect_symbol_end(); it != ie; ++it) {
1099 // Indirect symbols in the non lazy symbol pointer section have some
1100 // special handling.
1101 const MCSectionMachO &Section =
1102 static_cast<const MCSectionMachO&>(it->SectionData->getSection());
1103 if (Section.getType() == MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS) {
1104 // If this symbol is defined and internal, mark it as such.
1105 if (it->Symbol->isDefined() &&
1106 !Asm.getSymbolData(*it->Symbol).isExternal()) {
1107 uint32_t Flags = ISF_Local;
1108 if (it->Symbol->isAbsolute())
1109 Flags |= ISF_Absolute;
1115 Write32(Asm.getSymbolData(*it->Symbol).getIndex());
1118 // FIXME: Check that offsets match computed ones.
1120 // Write the symbol table entries.
1121 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1122 WriteNlist(LocalSymbolData[i], Layout);
1123 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1124 WriteNlist(ExternalSymbolData[i], Layout);
1125 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1126 WriteNlist(UndefinedSymbolData[i], Layout);
1128 // Write the string table.
1129 OS << StringTable.str();
1136 MachObjectWriter::MachObjectWriter(raw_ostream &OS,
1138 bool IsLittleEndian)
1139 : MCObjectWriter(OS, IsLittleEndian)
1141 Impl = new MachObjectWriterImpl(this, Is64Bit);
1144 MachObjectWriter::~MachObjectWriter() {
1145 delete (MachObjectWriterImpl*) Impl;
1148 void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
1149 ((MachObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
1152 void MachObjectWriter::RecordRelocation(const MCAssembler &Asm,
1153 const MCAsmLayout &Layout,
1154 const MCFragment *Fragment,
1155 const MCAsmFixup &Fixup, MCValue Target,
1156 uint64_t &FixedValue) {
1157 ((MachObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
1158 Target, FixedValue);
1161 void MachObjectWriter::WriteObject(const MCAssembler &Asm,
1162 const MCAsmLayout &Layout) {
1163 ((MachObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);