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 const MCSectionMachO &Section = cast<MCSectionMachO>(SD.getSection());
308 WriteBytes(Section.getSectionName(), 16);
309 WriteBytes(Section.getSegmentName(), 16);
311 Write64(Layout.getSectionAddress(&SD)); // address
312 Write64(SectionSize); // size
314 Write32(Layout.getSectionAddress(&SD)); // address
315 Write32(SectionSize); // size
319 unsigned Flags = Section.getTypeAndAttributes();
320 if (SD.hasInstructions())
321 Flags |= MCSectionMachO::S_ATTR_SOME_INSTRUCTIONS;
323 assert(isPowerOf2_32(SD.getAlignment()) && "Invalid alignment!");
324 Write32(Log2_32(SD.getAlignment()));
325 Write32(NumRelocations ? RelocationsStart : 0);
326 Write32(NumRelocations);
328 Write32(0); // reserved1
329 Write32(Section.getStubSize()); // reserved2
331 Write32(0); // reserved3
333 assert(OS.tell() - Start == Is64Bit ? Section64Size : Section32Size);
336 void WriteSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
337 uint32_t StringTableOffset,
338 uint32_t StringTableSize) {
339 // struct symtab_command (24 bytes)
341 uint64_t Start = OS.tell();
345 Write32(SymtabLoadCommandSize);
346 Write32(SymbolOffset);
348 Write32(StringTableOffset);
349 Write32(StringTableSize);
351 assert(OS.tell() - Start == SymtabLoadCommandSize);
354 void WriteDysymtabLoadCommand(uint32_t FirstLocalSymbol,
355 uint32_t NumLocalSymbols,
356 uint32_t FirstExternalSymbol,
357 uint32_t NumExternalSymbols,
358 uint32_t FirstUndefinedSymbol,
359 uint32_t NumUndefinedSymbols,
360 uint32_t IndirectSymbolOffset,
361 uint32_t NumIndirectSymbols) {
362 // struct dysymtab_command (80 bytes)
364 uint64_t Start = OS.tell();
367 Write32(LCT_Dysymtab);
368 Write32(DysymtabLoadCommandSize);
369 Write32(FirstLocalSymbol);
370 Write32(NumLocalSymbols);
371 Write32(FirstExternalSymbol);
372 Write32(NumExternalSymbols);
373 Write32(FirstUndefinedSymbol);
374 Write32(NumUndefinedSymbols);
375 Write32(0); // tocoff
377 Write32(0); // modtaboff
378 Write32(0); // nmodtab
379 Write32(0); // extrefsymoff
380 Write32(0); // nextrefsyms
381 Write32(IndirectSymbolOffset);
382 Write32(NumIndirectSymbols);
383 Write32(0); // extreloff
384 Write32(0); // nextrel
385 Write32(0); // locreloff
386 Write32(0); // nlocrel
388 assert(OS.tell() - Start == DysymtabLoadCommandSize);
391 void WriteNlist(MachSymbolData &MSD, const MCAsmLayout &Layout) {
392 MCSymbolData &Data = *MSD.SymbolData;
393 const MCSymbol &Symbol = Data.getSymbol();
395 uint16_t Flags = Data.getFlags();
396 uint32_t Address = 0;
398 // Set the N_TYPE bits. See <mach-o/nlist.h>.
400 // FIXME: Are the prebound or indirect fields possible here?
401 if (Symbol.isUndefined())
402 Type = STT_Undefined;
403 else if (Symbol.isAbsolute())
408 // FIXME: Set STAB bits.
410 if (Data.isPrivateExtern())
411 Type |= STF_PrivateExtern;
414 if (Data.isExternal() || Symbol.isUndefined())
415 Type |= STF_External;
417 // Compute the symbol address.
418 if (Symbol.isDefined()) {
419 if (Symbol.isAbsolute()) {
420 Address = cast<MCConstantExpr>(Symbol.getVariableValue())->getValue();
422 Address = Layout.getSymbolAddress(&Data);
424 } else if (Data.isCommon()) {
425 // Common symbols are encoded with the size in the address
426 // field, and their alignment in the flags.
427 Address = Data.getCommonSize();
429 // Common alignment is packed into the 'desc' bits.
430 if (unsigned Align = Data.getCommonAlignment()) {
431 unsigned Log2Size = Log2_32(Align);
432 assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
434 report_fatal_error("invalid 'common' alignment '" +
436 // FIXME: Keep this mask with the SymbolFlags enumeration.
437 Flags = (Flags & 0xF0FF) | (Log2Size << 8);
441 // struct nlist (12 bytes)
443 Write32(MSD.StringIndex);
445 Write8(MSD.SectionIndex);
447 // The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
456 // FIXME: We really need to improve the relocation validation. Basically, we
457 // want to implement a separate computation which evaluates the relocation
458 // entry as the linker would, and verifies that the resultant fixup value is
459 // exactly what the encoder wanted. This will catch several classes of
462 // - Relocation entry bugs, the two algorithms are unlikely to have the same
465 // - Relaxation issues, where we forget to relax something.
467 // - Input errors, where something cannot be correctly encoded. 'as' allows
468 // these through in many cases.
470 void RecordX86_64Relocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
471 const MCFragment *Fragment,
472 const MCAsmFixup &Fixup, MCValue Target,
473 uint64_t &FixedValue) {
474 unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
475 unsigned IsRIPRel = isFixupKindRIPRel(Fixup.Kind);
476 unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
479 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.Offset;
480 uint32_t FixupAddress = Layout.getFragmentAddress(Fragment) + Fixup.Offset;
483 unsigned IsExtern = 0;
486 Value = Target.getConstant();
489 // Compensate for the relocation offset, Darwin x86_64 relocations only
490 // have the addend and appear to have attempted to define it to be the
491 // actual expression addend without the PCrel bias. However, instructions
492 // with data following the relocation are not accomodated for (see comment
493 // below regarding SIGNED{1,2,4}), so it isn't exactly that either.
494 Value += 1LL << Log2Size;
497 if (Target.isAbsolute()) { // constant
498 // SymbolNum of 0 indicates the absolute section.
499 Type = RIT_X86_64_Unsigned;
502 // FIXME: I believe this is broken, I don't think the linker can
503 // understand it. I think it would require a local relocation, but I'm not
504 // sure if that would work either. The official way to get an absolute
505 // PCrel relocation is to use an absolute symbol (which we don't support
509 Type = RIT_X86_64_Branch;
511 } else if (Target.getSymB()) { // A - B + constant
512 const MCSymbol *A = &Target.getSymA()->getSymbol();
513 MCSymbolData &A_SD = Asm.getSymbolData(*A);
514 const MCSymbolData *A_Base = Asm.getAtom(Layout, &A_SD);
516 const MCSymbol *B = &Target.getSymB()->getSymbol();
517 MCSymbolData &B_SD = Asm.getSymbolData(*B);
518 const MCSymbolData *B_Base = Asm.getAtom(Layout, &B_SD);
520 // Neither symbol can be modified.
521 if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
522 Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
523 report_fatal_error("unsupported relocation of modified symbol");
525 // We don't support PCrel relocations of differences. Darwin 'as' doesn't
526 // implement most of these correctly.
528 report_fatal_error("unsupported pc-relative relocation of difference");
530 // We don't currently support any situation where one or both of the
531 // symbols would require a local relocation. This is almost certainly
532 // unused and may not be possible to encode correctly.
533 if (!A_Base || !B_Base)
534 report_fatal_error("unsupported local relocations in difference");
536 // Darwin 'as' doesn't emit correct relocations for this (it ends up with
537 // a single SIGNED relocation); reject it for now.
538 if (A_Base == B_Base)
539 report_fatal_error("unsupported relocation with identical base");
541 Value += Layout.getSymbolAddress(&A_SD) - Layout.getSymbolAddress(A_Base);
542 Value -= Layout.getSymbolAddress(&B_SD) - Layout.getSymbolAddress(B_Base);
544 Index = A_Base->getIndex();
546 Type = RIT_X86_64_Unsigned;
548 MachRelocationEntry MRE;
549 MRE.Word0 = FixupOffset;
550 MRE.Word1 = ((Index << 0) |
555 Relocations[Fragment->getParent()].push_back(MRE);
557 Index = B_Base->getIndex();
559 Type = RIT_X86_64_Subtractor;
561 const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
562 MCSymbolData &SD = Asm.getSymbolData(*Symbol);
563 const MCSymbolData *Base = Asm.getAtom(Layout, &SD);
565 // Relocations inside debug sections always use local relocations when
566 // possible. This seems to be done because the debugger doesn't fully
567 // understand x86_64 relocation entries, and expects to find values that
568 // have already been fixed up.
569 if (Symbol->isInSection()) {
570 const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
571 Fragment->getParent()->getSection());
572 if (Section.hasAttribute(MCSectionMachO::S_ATTR_DEBUG))
576 // x86_64 almost always uses external relocations, except when there is no
577 // symbol to use as a base address (a local symbol with no preceeding
578 // non-local symbol).
580 Index = Base->getIndex();
583 // Add the local offset, if needed.
585 Value += Layout.getSymbolAddress(&SD) - Layout.getSymbolAddress(Base);
586 } else if (Symbol->isInSection()) {
587 // The index is the section ordinal (1-based).
588 Index = SD.getFragment()->getParent()->getOrdinal() + 1;
590 Value += Layout.getSymbolAddress(&SD);
593 Value -= FixupAddress + (1 << Log2Size);
595 report_fatal_error("unsupported relocation of undefined symbol '" +
596 Symbol->getName() + "'");
599 MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
602 if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
603 // x86_64 distinguishes movq foo@GOTPCREL so that the linker can
604 // rewrite the movq to an leaq at link time if the symbol ends up in
605 // the same linkage unit.
606 if (unsigned(Fixup.Kind) == X86::reloc_riprel_4byte_movq_load)
607 Type = RIT_X86_64_GOTLoad;
609 Type = RIT_X86_64_GOT;
610 } else if (Modifier != MCSymbolRefExpr::VK_None) {
611 report_fatal_error("unsupported symbol modifier in relocation");
613 Type = RIT_X86_64_Signed;
615 // The Darwin x86_64 relocation format has a problem where it cannot
616 // encode an address (L<foo> + <constant>) which is outside the atom
617 // containing L<foo>. Generally, this shouldn't occur but it does
618 // happen when we have a RIPrel instruction with data following the
619 // relocation entry (e.g., movb $012, L0(%rip)). Even with the PCrel
620 // adjustment Darwin x86_64 uses, the offset is still negative and
621 // the linker has no way to recognize this.
623 // To work around this, Darwin uses several special relocation types
624 // to indicate the offsets. However, the specification or
625 // implementation of these seems to also be incomplete; they should
626 // adjust the addend as well based on the actual encoded instruction
627 // (the additional bias), but instead appear to just look at the
629 switch (-(Target.getConstant() + (1LL << Log2Size))) {
630 case 1: Type = RIT_X86_64_Signed1; break;
631 case 2: Type = RIT_X86_64_Signed2; break;
632 case 4: Type = RIT_X86_64_Signed4; break;
636 if (Modifier != MCSymbolRefExpr::VK_None)
637 report_fatal_error("unsupported symbol modifier in branch "
640 Type = RIT_X86_64_Branch;
643 if (Modifier == MCSymbolRefExpr::VK_GOT) {
644 Type = RIT_X86_64_GOT;
645 } else if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
646 // GOTPCREL is allowed as a modifier on non-PCrel instructions, in
647 // which case all we do is set the PCrel bit in the relocation entry;
648 // this is used with exception handling, for example. The source is
649 // required to include any necessary offset directly.
650 Type = RIT_X86_64_GOT;
652 } else if (Modifier != MCSymbolRefExpr::VK_None)
653 report_fatal_error("unsupported symbol modifier in relocation");
655 Type = RIT_X86_64_Unsigned;
659 // x86_64 always writes custom values into the fixups.
662 // struct relocation_info (8 bytes)
663 MachRelocationEntry MRE;
664 MRE.Word0 = FixupOffset;
665 MRE.Word1 = ((Index << 0) |
670 Relocations[Fragment->getParent()].push_back(MRE);
673 void RecordScatteredRelocation(const MCAssembler &Asm,
674 const MCAsmLayout &Layout,
675 const MCFragment *Fragment,
676 const MCAsmFixup &Fixup, MCValue Target,
677 uint64_t &FixedValue) {
678 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.Offset;
679 unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
680 unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
681 unsigned Type = RIT_Vanilla;
684 const MCSymbol *A = &Target.getSymA()->getSymbol();
685 MCSymbolData *A_SD = &Asm.getSymbolData(*A);
687 if (!A_SD->getFragment())
688 report_fatal_error("symbol '" + A->getName() +
689 "' can not be undefined in a subtraction expression");
691 uint32_t Value = Layout.getSymbolAddress(A_SD);
694 if (const MCSymbolRefExpr *B = Target.getSymB()) {
695 MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
697 if (!B_SD->getFragment())
698 report_fatal_error("symbol '" + B->getSymbol().getName() +
699 "' can not be undefined in a subtraction expression");
701 // Select the appropriate difference relocation type.
703 // Note that there is no longer any semantic difference between these two
704 // relocation types from the linkers point of view, this is done solely
705 // for pedantic compatibility with 'as'.
706 Type = A_SD->isExternal() ? RIT_Difference : RIT_LocalDifference;
707 Value2 = Layout.getSymbolAddress(B_SD);
710 // Relocations are written out in reverse order, so the PAIR comes first.
711 if (Type == RIT_Difference || Type == RIT_LocalDifference) {
712 MachRelocationEntry MRE;
713 MRE.Word0 = ((0 << 0) |
719 Relocations[Fragment->getParent()].push_back(MRE);
722 MachRelocationEntry MRE;
723 MRE.Word0 = ((FixupOffset << 0) |
729 Relocations[Fragment->getParent()].push_back(MRE);
732 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
733 const MCFragment *Fragment, const MCAsmFixup &Fixup,
734 MCValue Target, uint64_t &FixedValue) {
736 RecordX86_64Relocation(Asm, Layout, Fragment, Fixup, Target, FixedValue);
740 unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
741 unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
743 // If this is a difference or a defined symbol plus an offset, then we need
744 // a scattered relocation entry.
745 // Differences always require scattered relocations.
746 if (Target.getSymB())
747 return RecordScatteredRelocation(Asm, Layout, Fragment, Fixup,
750 // Get the symbol data, if any.
751 MCSymbolData *SD = 0;
752 if (Target.getSymA())
753 SD = &Asm.getSymbolData(Target.getSymA()->getSymbol());
755 // If this is an internal relocation with an offset, it also needs a
756 // scattered relocation entry.
757 uint32_t Offset = Target.getConstant();
759 Offset += 1 << Log2Size;
760 if (Offset && SD && !doesSymbolRequireExternRelocation(SD))
761 return RecordScatteredRelocation(Asm, Layout, Fragment, Fixup,
765 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.Offset;
768 unsigned IsExtern = 0;
771 if (Target.isAbsolute()) { // constant
772 // SymbolNum of 0 indicates the absolute section.
774 // FIXME: Currently, these are never generated (see code below). I cannot
775 // find a case where they are actually emitted.
779 // Check whether we need an external or internal relocation.
780 if (doesSymbolRequireExternRelocation(SD)) {
782 Index = SD->getIndex();
783 // For external relocations, make sure to offset the fixup value to
784 // compensate for the addend of the symbol address, if it was
785 // undefined. This occurs with weak definitions, for example.
786 if (!SD->Symbol->isUndefined())
787 FixedValue -= Layout.getSymbolAddress(SD);
790 // The index is the section ordinal (1-based).
791 Index = SD->getFragment()->getParent()->getOrdinal() + 1;
792 Value = Layout.getSymbolAddress(SD);
798 // struct relocation_info (8 bytes)
799 MachRelocationEntry MRE;
800 MRE.Word0 = FixupOffset;
801 MRE.Word1 = ((Index << 0) |
806 Relocations[Fragment->getParent()].push_back(MRE);
809 void BindIndirectSymbols(MCAssembler &Asm) {
810 // This is the point where 'as' creates actual symbols for indirect symbols
811 // (in the following two passes). It would be easier for us to do this
812 // sooner when we see the attribute, but that makes getting the order in the
813 // symbol table much more complicated than it is worth.
815 // FIXME: Revisit this when the dust settles.
817 // Bind non lazy symbol pointers first.
818 for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
819 ie = Asm.indirect_symbol_end(); it != ie; ++it) {
820 const MCSectionMachO &Section =
821 cast<MCSectionMachO>(it->SectionData->getSection());
823 if (Section.getType() != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
826 Asm.getOrCreateSymbolData(*it->Symbol);
829 // Then lazy symbol pointers and symbol stubs.
830 for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
831 ie = Asm.indirect_symbol_end(); it != ie; ++it) {
832 const MCSectionMachO &Section =
833 cast<MCSectionMachO>(it->SectionData->getSection());
835 if (Section.getType() != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
836 Section.getType() != MCSectionMachO::S_SYMBOL_STUBS)
839 // Set the symbol type to undefined lazy, but only on construction.
841 // FIXME: Do not hardcode.
843 MCSymbolData &Entry = Asm.getOrCreateSymbolData(*it->Symbol, &Created);
845 Entry.setFlags(Entry.getFlags() | 0x0001);
849 /// ComputeSymbolTable - Compute the symbol table data
851 /// \param StringTable [out] - The string table data.
852 /// \param StringIndexMap [out] - Map from symbol names to offsets in the
854 void ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
855 std::vector<MachSymbolData> &LocalSymbolData,
856 std::vector<MachSymbolData> &ExternalSymbolData,
857 std::vector<MachSymbolData> &UndefinedSymbolData) {
858 // Build section lookup table.
859 DenseMap<const MCSection*, uint8_t> SectionIndexMap;
861 for (MCAssembler::iterator it = Asm.begin(),
862 ie = Asm.end(); it != ie; ++it, ++Index)
863 SectionIndexMap[&it->getSection()] = Index;
864 assert(Index <= 256 && "Too many sections!");
866 // Index 0 is always the empty string.
867 StringMap<uint64_t> StringIndexMap;
868 StringTable += '\x00';
870 // Build the symbol arrays and the string table, but only for non-local
873 // The particular order that we collect the symbols and create the string
874 // table, then sort the symbols is chosen to match 'as'. Even though it
875 // doesn't matter for correctness, this is important for letting us diff .o
877 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
878 ie = Asm.symbol_end(); it != ie; ++it) {
879 const MCSymbol &Symbol = it->getSymbol();
881 // Ignore non-linker visible symbols.
882 if (!Asm.isSymbolLinkerVisible(it))
885 if (!it->isExternal() && !Symbol.isUndefined())
888 uint64_t &Entry = StringIndexMap[Symbol.getName()];
890 Entry = StringTable.size();
891 StringTable += Symbol.getName();
892 StringTable += '\x00';
897 MSD.StringIndex = Entry;
899 if (Symbol.isUndefined()) {
900 MSD.SectionIndex = 0;
901 UndefinedSymbolData.push_back(MSD);
902 } else if (Symbol.isAbsolute()) {
903 MSD.SectionIndex = 0;
904 ExternalSymbolData.push_back(MSD);
906 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
907 assert(MSD.SectionIndex && "Invalid section index!");
908 ExternalSymbolData.push_back(MSD);
912 // Now add the data for local symbols.
913 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
914 ie = Asm.symbol_end(); it != ie; ++it) {
915 const MCSymbol &Symbol = it->getSymbol();
917 // Ignore non-linker visible symbols.
918 if (!Asm.isSymbolLinkerVisible(it))
921 if (it->isExternal() || Symbol.isUndefined())
924 uint64_t &Entry = StringIndexMap[Symbol.getName()];
926 Entry = StringTable.size();
927 StringTable += Symbol.getName();
928 StringTable += '\x00';
933 MSD.StringIndex = Entry;
935 if (Symbol.isAbsolute()) {
936 MSD.SectionIndex = 0;
937 LocalSymbolData.push_back(MSD);
939 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
940 assert(MSD.SectionIndex && "Invalid section index!");
941 LocalSymbolData.push_back(MSD);
945 // External and undefined symbols are required to be in lexicographic order.
946 std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
947 std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
949 // Set the symbol indices.
951 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
952 LocalSymbolData[i].SymbolData->setIndex(Index++);
953 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
954 ExternalSymbolData[i].SymbolData->setIndex(Index++);
955 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
956 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
958 // The string table is padded to a multiple of 4.
959 while (StringTable.size() % 4)
960 StringTable += '\x00';
963 void ExecutePostLayoutBinding(MCAssembler &Asm) {
964 // Create symbol data for any indirect symbols.
965 BindIndirectSymbols(Asm);
967 // Compute symbol table information and bind symbol indices.
968 ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
969 UndefinedSymbolData);
972 void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout) {
973 unsigned NumSections = Asm.size();
975 // The section data starts after the header, the segment load command (and
976 // section headers) and the symbol table.
977 unsigned NumLoadCommands = 1;
978 uint64_t LoadCommandsSize = Is64Bit ?
979 SegmentLoadCommand64Size + NumSections * Section64Size :
980 SegmentLoadCommand32Size + NumSections * Section32Size;
982 // Add the symbol table load command sizes, if used.
983 unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
984 UndefinedSymbolData.size();
986 NumLoadCommands += 2;
987 LoadCommandsSize += SymtabLoadCommandSize + DysymtabLoadCommandSize;
990 // Compute the total size of the section data, as well as its file size and
992 uint64_t SectionDataStart = (Is64Bit ? Header64Size : Header32Size)
994 uint64_t SectionDataSize = 0;
995 uint64_t SectionDataFileSize = 0;
997 for (MCAssembler::const_iterator it = Asm.begin(),
998 ie = Asm.end(); it != ie; ++it) {
999 const MCSectionData &SD = *it;
1000 uint64_t Address = Layout.getSectionAddress(&SD);
1001 uint64_t Size = Layout.getSectionSize(&SD);
1002 uint64_t FileSize = Layout.getSectionFileSize(&SD);
1004 VMSize = std::max(VMSize, Address + Size);
1006 if (Asm.getBackend().isVirtualSection(SD.getSection()))
1009 SectionDataSize = std::max(SectionDataSize, Address + Size);
1010 SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
1013 // The section data is padded to 4 bytes.
1015 // FIXME: Is this machine dependent?
1016 unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
1017 SectionDataFileSize += SectionDataPadding;
1019 // Write the prolog, starting with the header and load command...
1020 WriteHeader(NumLoadCommands, LoadCommandsSize,
1021 Asm.getSubsectionsViaSymbols());
1022 WriteSegmentLoadCommand(NumSections, VMSize,
1023 SectionDataStart, SectionDataSize);
1025 // ... and then the section headers.
1026 uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
1027 for (MCAssembler::const_iterator it = Asm.begin(),
1028 ie = Asm.end(); it != ie; ++it) {
1029 std::vector<MachRelocationEntry> &Relocs = Relocations[it];
1030 unsigned NumRelocs = Relocs.size();
1031 uint64_t SectionStart = SectionDataStart + Layout.getSectionAddress(it);
1032 WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
1033 RelocTableEnd += NumRelocs * RelocationInfoSize;
1036 // Write the symbol table load command, if used.
1038 unsigned FirstLocalSymbol = 0;
1039 unsigned NumLocalSymbols = LocalSymbolData.size();
1040 unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
1041 unsigned NumExternalSymbols = ExternalSymbolData.size();
1042 unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
1043 unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
1044 unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
1045 unsigned NumSymTabSymbols =
1046 NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
1047 uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
1048 uint64_t IndirectSymbolOffset = 0;
1050 // If used, the indirect symbols are written after the section data.
1051 if (NumIndirectSymbols)
1052 IndirectSymbolOffset = RelocTableEnd;
1054 // The symbol table is written after the indirect symbol data.
1055 uint64_t SymbolTableOffset = RelocTableEnd + IndirectSymbolSize;
1057 // The string table is written after symbol table.
1058 uint64_t StringTableOffset =
1059 SymbolTableOffset + NumSymTabSymbols * (Is64Bit ? Nlist64Size :
1061 WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
1062 StringTableOffset, StringTable.size());
1064 WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
1065 FirstExternalSymbol, NumExternalSymbols,
1066 FirstUndefinedSymbol, NumUndefinedSymbols,
1067 IndirectSymbolOffset, NumIndirectSymbols);
1070 // Write the actual section data.
1071 for (MCAssembler::const_iterator it = Asm.begin(),
1072 ie = Asm.end(); it != ie; ++it)
1073 Asm.WriteSectionData(it, Layout, Writer);
1075 // Write the extra padding.
1076 WriteZeros(SectionDataPadding);
1078 // Write the relocation entries.
1079 for (MCAssembler::const_iterator it = Asm.begin(),
1080 ie = Asm.end(); it != ie; ++it) {
1081 // Write the section relocation entries, in reverse order to match 'as'
1082 // (approximately, the exact algorithm is more complicated than this).
1083 std::vector<MachRelocationEntry> &Relocs = Relocations[it];
1084 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1085 Write32(Relocs[e - i - 1].Word0);
1086 Write32(Relocs[e - i - 1].Word1);
1090 // Write the symbol table data, if used.
1092 // Write the indirect symbol entries.
1093 for (MCAssembler::const_indirect_symbol_iterator
1094 it = Asm.indirect_symbol_begin(),
1095 ie = Asm.indirect_symbol_end(); it != ie; ++it) {
1096 // Indirect symbols in the non lazy symbol pointer section have some
1097 // special handling.
1098 const MCSectionMachO &Section =
1099 static_cast<const MCSectionMachO&>(it->SectionData->getSection());
1100 if (Section.getType() == MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS) {
1101 // If this symbol is defined and internal, mark it as such.
1102 if (it->Symbol->isDefined() &&
1103 !Asm.getSymbolData(*it->Symbol).isExternal()) {
1104 uint32_t Flags = ISF_Local;
1105 if (it->Symbol->isAbsolute())
1106 Flags |= ISF_Absolute;
1112 Write32(Asm.getSymbolData(*it->Symbol).getIndex());
1115 // FIXME: Check that offsets match computed ones.
1117 // Write the symbol table entries.
1118 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1119 WriteNlist(LocalSymbolData[i], Layout);
1120 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1121 WriteNlist(ExternalSymbolData[i], Layout);
1122 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1123 WriteNlist(UndefinedSymbolData[i], Layout);
1125 // Write the string table.
1126 OS << StringTable.str();
1133 MachObjectWriter::MachObjectWriter(raw_ostream &OS,
1135 bool IsLittleEndian)
1136 : MCObjectWriter(OS, IsLittleEndian)
1138 Impl = new MachObjectWriterImpl(this, Is64Bit);
1141 MachObjectWriter::~MachObjectWriter() {
1142 delete (MachObjectWriterImpl*) Impl;
1145 void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
1146 ((MachObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
1149 void MachObjectWriter::RecordRelocation(const MCAssembler &Asm,
1150 const MCAsmLayout &Layout,
1151 const MCFragment *Fragment,
1152 const MCAsmFixup &Fixup, MCValue Target,
1153 uint64_t &FixedValue) {
1154 ((MachObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
1155 Target, FixedValue);
1158 void MachObjectWriter::WriteObject(const MCAssembler &Asm,
1159 const MCAsmLayout &Layout) {
1160 ((MachObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);