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llvm-project/llvm/lib/MC/MachObjectWriter.cpp

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//===- lib/MC/MachObjectWriter.cpp - Mach-O File Writer -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MachObjectWriter.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCMachOSymbolFlags.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MachO.h"
#include "llvm/Target/TargetAsmBackend.h"
// FIXME: Gross.
#include "../Target/X86/X86FixupKinds.h"
#include <vector>
using namespace llvm;
// FIXME: this has been copied from (or to) X86AsmBackend.cpp
static unsigned getFixupKindLog2Size(unsigned Kind) {
switch (Kind) {
default: llvm_unreachable("invalid fixup kind!");
case X86::reloc_pcrel_1byte:
case FK_Data_1: return 0;
case X86::reloc_pcrel_2byte:
case FK_Data_2: return 1;
case X86::reloc_pcrel_4byte:
case X86::reloc_riprel_4byte:
case X86::reloc_riprel_4byte_movq_load:
case X86::reloc_signed_4byte:
case FK_Data_4: return 2;
case FK_Data_8: return 3;
}
}
static bool isFixupKindPCRel(unsigned Kind) {
switch (Kind) {
default:
return false;
case X86::reloc_pcrel_1byte:
case X86::reloc_pcrel_2byte:
case X86::reloc_pcrel_4byte:
case X86::reloc_riprel_4byte:
case X86::reloc_riprel_4byte_movq_load:
return true;
}
}
static bool isFixupKindRIPRel(unsigned Kind) {
return Kind == X86::reloc_riprel_4byte ||
Kind == X86::reloc_riprel_4byte_movq_load;
}
static bool doesSymbolRequireExternRelocation(MCSymbolData *SD) {
// Undefined symbols are always extern.
if (SD->Symbol->isUndefined())
return true;
// References to weak definitions require external relocation entries; the
// definition may not always be the one in the same object file.
if (SD->getFlags() & SF_WeakDefinition)
return true;
// Otherwise, we can use an internal relocation.
return false;
}
static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
const MCValue Target,
const MCSymbolData *BaseSymbol) {
// The effective fixup address is
// addr(atom(A)) + offset(A)
// - addr(atom(B)) - offset(B)
// - addr(BaseSymbol) + <fixup offset from base symbol>
// and the offsets are not relocatable, so the fixup is fully resolved when
// addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
//
// Note that "false" is almost always conservatively correct (it means we emit
// a relocation which is unnecessary), except when it would force us to emit a
// relocation which the target cannot encode.
const MCSymbolData *A_Base = 0, *B_Base = 0;
if (const MCSymbolRefExpr *A = Target.getSymA()) {
// Modified symbol references cannot be resolved.
if (A->getKind() != MCSymbolRefExpr::VK_None)
return false;
A_Base = Asm.getAtom(&Asm.getSymbolData(A->getSymbol()));
if (!A_Base)
return false;
}
if (const MCSymbolRefExpr *B = Target.getSymB()) {
// Modified symbol references cannot be resolved.
if (B->getKind() != MCSymbolRefExpr::VK_None)
return false;
B_Base = Asm.getAtom(&Asm.getSymbolData(B->getSymbol()));
if (!B_Base)
return false;
}
// If there is no base, A and B have to be the same atom for this fixup to be
// fully resolved.
if (!BaseSymbol)
return A_Base == B_Base;
// Otherwise, B must be missing and A must be the base.
return !B_Base && BaseSymbol == A_Base;
}
static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm,
const MCValue Target,
const MCSection *BaseSection) {
// The effective fixup address is
// addr(atom(A)) + offset(A)
// - addr(atom(B)) - offset(B)
// - addr(<base symbol>) + <fixup offset from base symbol>
// and the offsets are not relocatable, so the fixup is fully resolved when
// addr(atom(A)) - addr(atom(B)) - addr(<base symbol>)) == 0.
//
// The simple (Darwin, except on x86_64) way of dealing with this was to
// assume that any reference to a temporary symbol *must* be a temporary
// symbol in the same atom, unless the sections differ. Therefore, any PCrel
// relocation to a temporary symbol (in the same section) is fully
// resolved. This also works in conjunction with absolutized .set, which
// requires the compiler to use .set to absolutize the differences between
// symbols which the compiler knows to be assembly time constants, so we don't
// need to worry about considering symbol differences fully resolved.
// Non-relative fixups are only resolved if constant.
if (!BaseSection)
return Target.isAbsolute();
// Otherwise, relative fixups are only resolved if not a difference and the
// target is a temporary in the same section.
if (Target.isAbsolute() || Target.getSymB())
return false;
const MCSymbol *A = &Target.getSymA()->getSymbol();
if (!A->isTemporary() || !A->isInSection() ||
&A->getSection() != BaseSection)
return false;
return true;
}
namespace {
class MachObjectWriterImpl {
// See <mach-o/loader.h>.
enum {
Header_Magic32 = 0xFEEDFACE,
Header_Magic64 = 0xFEEDFACF
};
enum {
Header32Size = 28,
Header64Size = 32,
SegmentLoadCommand32Size = 56,
SegmentLoadCommand64Size = 72,
Section32Size = 68,
Section64Size = 80,
SymtabLoadCommandSize = 24,
DysymtabLoadCommandSize = 80,
Nlist32Size = 12,
Nlist64Size = 16,
RelocationInfoSize = 8
};
enum HeaderFileType {
HFT_Object = 0x1
};
enum HeaderFlags {
HF_SubsectionsViaSymbols = 0x2000
};
enum LoadCommandType {
LCT_Segment = 0x1,
LCT_Symtab = 0x2,
LCT_Dysymtab = 0xb,
LCT_Segment64 = 0x19
};
// See <mach-o/nlist.h>.
enum SymbolTypeType {
STT_Undefined = 0x00,
STT_Absolute = 0x02,
STT_Section = 0x0e
};
enum SymbolTypeFlags {
// If any of these bits are set, then the entry is a stab entry number (see
// <mach-o/stab.h>. Otherwise the other masks apply.
STF_StabsEntryMask = 0xe0,
STF_TypeMask = 0x0e,
STF_External = 0x01,
STF_PrivateExtern = 0x10
};
/// IndirectSymbolFlags - Flags for encoding special values in the indirect
/// symbol entry.
enum IndirectSymbolFlags {
ISF_Local = 0x80000000,
ISF_Absolute = 0x40000000
};
/// RelocationFlags - Special flags for addresses.
enum RelocationFlags {
RF_Scattered = 0x80000000
};
enum RelocationInfoType {
RIT_Vanilla = 0,
RIT_Pair = 1,
RIT_Difference = 2,
RIT_PreboundLazyPointer = 3,
RIT_LocalDifference = 4,
RIT_TLV = 5
};
/// X86_64 uses its own relocation types.
enum RelocationInfoTypeX86_64 {
RIT_X86_64_Unsigned = 0,
RIT_X86_64_Signed = 1,
RIT_X86_64_Branch = 2,
RIT_X86_64_GOTLoad = 3,
RIT_X86_64_GOT = 4,
RIT_X86_64_Subtractor = 5,
RIT_X86_64_Signed1 = 6,
RIT_X86_64_Signed2 = 7,
RIT_X86_64_Signed4 = 8,
RIT_X86_64_TLV = 9
};
/// MachSymbolData - Helper struct for containing some precomputed information
/// on symbols.
struct MachSymbolData {
MCSymbolData *SymbolData;
uint64_t StringIndex;
uint8_t SectionIndex;
// Support lexicographic sorting.
bool operator<(const MachSymbolData &RHS) const {
return SymbolData->getSymbol().getName() <
RHS.SymbolData->getSymbol().getName();
}
};
/// @name Relocation Data
/// @{
struct MachRelocationEntry {
uint32_t Word0;
uint32_t Word1;
};
llvm::DenseMap<const MCSectionData*,
std::vector<MachRelocationEntry> > Relocations;
llvm::DenseMap<const MCSectionData*, unsigned> IndirectSymBase;
/// @}
/// @name Symbol Table Data
/// @{
SmallString<256> StringTable;
std::vector<MachSymbolData> LocalSymbolData;
std::vector<MachSymbolData> ExternalSymbolData;
std::vector<MachSymbolData> UndefinedSymbolData;
/// @}
MachObjectWriter *Writer;
raw_ostream &OS;
unsigned Is64Bit : 1;
public:
MachObjectWriterImpl(MachObjectWriter *_Writer, bool _Is64Bit)
: Writer(_Writer), OS(Writer->getStream()), Is64Bit(_Is64Bit) {
}
void Write8(uint8_t Value) { Writer->Write8(Value); }
void Write16(uint16_t Value) { Writer->Write16(Value); }
void Write32(uint32_t Value) { Writer->Write32(Value); }
void Write64(uint64_t Value) { Writer->Write64(Value); }
void WriteZeros(unsigned N) { Writer->WriteZeros(N); }
void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
Writer->WriteBytes(Str, ZeroFillSize);
}
void WriteHeader(unsigned NumLoadCommands, unsigned LoadCommandsSize,
bool SubsectionsViaSymbols) {
uint32_t Flags = 0;
if (SubsectionsViaSymbols)
Flags |= HF_SubsectionsViaSymbols;
// struct mach_header (28 bytes) or
// struct mach_header_64 (32 bytes)
uint64_t Start = OS.tell();
(void) Start;
Write32(Is64Bit ? Header_Magic64 : Header_Magic32);
// FIXME: Support cputype.
Write32(Is64Bit ? MachO::CPUTypeX86_64 : MachO::CPUTypeI386);
// FIXME: Support cpusubtype.
Write32(MachO::CPUSubType_I386_ALL);
Write32(HFT_Object);
Write32(NumLoadCommands); // Object files have a single load command, the
// segment.
Write32(LoadCommandsSize);
Write32(Flags);
if (Is64Bit)
Write32(0); // reserved
assert(OS.tell() - Start == Is64Bit ? Header64Size : Header32Size);
}
/// WriteSegmentLoadCommand - Write a segment load command.
///
/// \arg NumSections - The number of sections in this segment.
/// \arg SectionDataSize - The total size of the sections.
void WriteSegmentLoadCommand(unsigned NumSections,
uint64_t VMSize,
uint64_t SectionDataStartOffset,
uint64_t SectionDataSize) {
// struct segment_command (56 bytes) or
// struct segment_command_64 (72 bytes)
uint64_t Start = OS.tell();
(void) Start;
unsigned SegmentLoadCommandSize = Is64Bit ? SegmentLoadCommand64Size :
SegmentLoadCommand32Size;
Write32(Is64Bit ? LCT_Segment64 : LCT_Segment);
Write32(SegmentLoadCommandSize +
NumSections * (Is64Bit ? Section64Size : Section32Size));
WriteBytes("", 16);
if (Is64Bit) {
Write64(0); // vmaddr
Write64(VMSize); // vmsize
Write64(SectionDataStartOffset); // file offset
Write64(SectionDataSize); // file size
} else {
Write32(0); // vmaddr
Write32(VMSize); // vmsize
Write32(SectionDataStartOffset); // file offset
Write32(SectionDataSize); // file size
}
Write32(0x7); // maxprot
Write32(0x7); // initprot
Write32(NumSections);
Write32(0); // flags
assert(OS.tell() - Start == SegmentLoadCommandSize);
}
void WriteSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCSectionData &SD, uint64_t FileOffset,
uint64_t RelocationsStart, unsigned NumRelocations) {
uint64_t SectionSize = Layout.getSectionSize(&SD);
// The offset is unused for virtual sections.
if (Asm.getBackend().isVirtualSection(SD.getSection())) {
assert(Layout.getSectionFileSize(&SD) == 0 && "Invalid file size!");
FileOffset = 0;
}
// struct section (68 bytes) or
// struct section_64 (80 bytes)
uint64_t Start = OS.tell();
(void) Start;
const MCSectionMachO &Section = cast<MCSectionMachO>(SD.getSection());
WriteBytes(Section.getSectionName(), 16);
WriteBytes(Section.getSegmentName(), 16);
if (Is64Bit) {
Write64(Layout.getSectionAddress(&SD)); // address
Write64(SectionSize); // size
} else {
Write32(Layout.getSectionAddress(&SD)); // address
Write32(SectionSize); // size
}
Write32(FileOffset);
unsigned Flags = Section.getTypeAndAttributes();
if (SD.hasInstructions())
Flags |= MCSectionMachO::S_ATTR_SOME_INSTRUCTIONS;
assert(isPowerOf2_32(SD.getAlignment()) && "Invalid alignment!");
Write32(Log2_32(SD.getAlignment()));
Write32(NumRelocations ? RelocationsStart : 0);
Write32(NumRelocations);
Write32(Flags);
Write32(IndirectSymBase.lookup(&SD)); // reserved1
Write32(Section.getStubSize()); // reserved2
if (Is64Bit)
Write32(0); // reserved3
assert(OS.tell() - Start == Is64Bit ? Section64Size : Section32Size);
}
void WriteSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
uint32_t StringTableOffset,
uint32_t StringTableSize) {
// struct symtab_command (24 bytes)
uint64_t Start = OS.tell();
(void) Start;
Write32(LCT_Symtab);
Write32(SymtabLoadCommandSize);
Write32(SymbolOffset);
Write32(NumSymbols);
Write32(StringTableOffset);
Write32(StringTableSize);
assert(OS.tell() - Start == SymtabLoadCommandSize);
}
void WriteDysymtabLoadCommand(uint32_t FirstLocalSymbol,
uint32_t NumLocalSymbols,
uint32_t FirstExternalSymbol,
uint32_t NumExternalSymbols,
uint32_t FirstUndefinedSymbol,
uint32_t NumUndefinedSymbols,
uint32_t IndirectSymbolOffset,
uint32_t NumIndirectSymbols) {
// struct dysymtab_command (80 bytes)
uint64_t Start = OS.tell();
(void) Start;
Write32(LCT_Dysymtab);
Write32(DysymtabLoadCommandSize);
Write32(FirstLocalSymbol);
Write32(NumLocalSymbols);
Write32(FirstExternalSymbol);
Write32(NumExternalSymbols);
Write32(FirstUndefinedSymbol);
Write32(NumUndefinedSymbols);
Write32(0); // tocoff
Write32(0); // ntoc
Write32(0); // modtaboff
Write32(0); // nmodtab
Write32(0); // extrefsymoff
Write32(0); // nextrefsyms
Write32(IndirectSymbolOffset);
Write32(NumIndirectSymbols);
Write32(0); // extreloff
Write32(0); // nextrel
Write32(0); // locreloff
Write32(0); // nlocrel
assert(OS.tell() - Start == DysymtabLoadCommandSize);
}
void WriteNlist(MachSymbolData &MSD, const MCAsmLayout &Layout) {
MCSymbolData &Data = *MSD.SymbolData;
const MCSymbol &Symbol = Data.getSymbol();
uint8_t Type = 0;
uint16_t Flags = Data.getFlags();
uint32_t Address = 0;
// Set the N_TYPE bits. See <mach-o/nlist.h>.
//
// FIXME: Are the prebound or indirect fields possible here?
if (Symbol.isUndefined())
Type = STT_Undefined;
else if (Symbol.isAbsolute())
Type = STT_Absolute;
else
Type = STT_Section;
// FIXME: Set STAB bits.
if (Data.isPrivateExtern())
Type |= STF_PrivateExtern;
// Set external bit.
if (Data.isExternal() || Symbol.isUndefined())
Type |= STF_External;
// Compute the symbol address.
if (Symbol.isDefined()) {
if (Symbol.isAbsolute()) {
Address = cast<MCConstantExpr>(Symbol.getVariableValue())->getValue();
} else {
Address = Layout.getSymbolAddress(&Data);
}
} else if (Data.isCommon()) {
// Common symbols are encoded with the size in the address
// field, and their alignment in the flags.
Address = Data.getCommonSize();
// Common alignment is packed into the 'desc' bits.
if (unsigned Align = Data.getCommonAlignment()) {
unsigned Log2Size = Log2_32(Align);
assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
if (Log2Size > 15)
report_fatal_error("invalid 'common' alignment '" +
Twine(Align) + "'");
// FIXME: Keep this mask with the SymbolFlags enumeration.
Flags = (Flags & 0xF0FF) | (Log2Size << 8);
}
}
// struct nlist (12 bytes)
Write32(MSD.StringIndex);
Write8(Type);
Write8(MSD.SectionIndex);
// The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
// value.
Write16(Flags);
if (Is64Bit)
Write64(Address);
else
Write32(Address);
}
// FIXME: We really need to improve the relocation validation. Basically, we
// want to implement a separate computation which evaluates the relocation
// entry as the linker would, and verifies that the resultant fixup value is
// exactly what the encoder wanted. This will catch several classes of
// problems:
//
// - Relocation entry bugs, the two algorithms are unlikely to have the same
// exact bug.
//
// - Relaxation issues, where we forget to relax something.
//
// - Input errors, where something cannot be correctly encoded. 'as' allows
// these through in many cases.
void RecordX86_64Relocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
unsigned IsPCRel = isFixupKindPCRel(Fixup.getKind());
unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind());
unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
// See <reloc.h>.
uint32_t FixupOffset =
Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
uint32_t FixupAddress =
Layout.getFragmentAddress(Fragment) + Fixup.getOffset();
int64_t Value = 0;
unsigned Index = 0;
unsigned IsExtern = 0;
unsigned Type = 0;
Value = Target.getConstant();
if (IsPCRel) {
// Compensate for the relocation offset, Darwin x86_64 relocations only
// have the addend and appear to have attempted to define it to be the
// actual expression addend without the PCrel bias. However, instructions
// with data following the relocation are not accomodated for (see comment
// below regarding SIGNED{1,2,4}), so it isn't exactly that either.
Value += 1LL << Log2Size;
}
if (Target.isAbsolute()) { // constant
// SymbolNum of 0 indicates the absolute section.
Type = RIT_X86_64_Unsigned;
Index = 0;
// FIXME: I believe this is broken, I don't think the linker can
// understand it. I think it would require a local relocation, but I'm not
// sure if that would work either. The official way to get an absolute
// PCrel relocation is to use an absolute symbol (which we don't support
// yet).
if (IsPCRel) {
IsExtern = 1;
Type = RIT_X86_64_Branch;
}
} else if (Target.getSymB()) { // A - B + constant
const MCSymbol *A = &Target.getSymA()->getSymbol();
MCSymbolData &A_SD = Asm.getSymbolData(*A);
const MCSymbolData *A_Base = Asm.getAtom(&A_SD);
const MCSymbol *B = &Target.getSymB()->getSymbol();
MCSymbolData &B_SD = Asm.getSymbolData(*B);
const MCSymbolData *B_Base = Asm.getAtom(&B_SD);
// Neither symbol can be modified.
if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
report_fatal_error("unsupported relocation of modified symbol");
// We don't support PCrel relocations of differences. Darwin 'as' doesn't
// implement most of these correctly.
if (IsPCRel)
report_fatal_error("unsupported pc-relative relocation of difference");
// The support for the situation where one or both of the symbols would
// require a local relocation is handled just like if the symbols were
// external. This is certainly used in the case of debug sections where
// the section has only temporary symbols and thus the symbols don't have
// base symbols. This is encoded using the section ordinal and
// non-extern relocation entries.
// Darwin 'as' doesn't emit correct relocations for this (it ends up with
// a single SIGNED relocation); reject it for now. Except the case where
// both symbols don't have a base, equal but both NULL.
if (A_Base == B_Base && A_Base)
report_fatal_error("unsupported relocation with identical base");
Value += Layout.getSymbolAddress(&A_SD) -
(A_Base == NULL ? 0 : Layout.getSymbolAddress(A_Base));
Value -= Layout.getSymbolAddress(&B_SD) -
(B_Base == NULL ? 0 : Layout.getSymbolAddress(B_Base));
if (A_Base) {
Index = A_Base->getIndex();
IsExtern = 1;
}
else {
Index = A_SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
}
Type = RIT_X86_64_Unsigned;
MachRelocationEntry MRE;
MRE.Word0 = FixupOffset;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Relocations[Fragment->getParent()].push_back(MRE);
if (B_Base) {
Index = B_Base->getIndex();
IsExtern = 1;
}
else {
Index = B_SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
}
Type = RIT_X86_64_Subtractor;
} else {
const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
MCSymbolData &SD = Asm.getSymbolData(*Symbol);
const MCSymbolData *Base = Asm.getAtom(&SD);
// Relocations inside debug sections always use local relocations when
// possible. This seems to be done because the debugger doesn't fully
// understand x86_64 relocation entries, and expects to find values that
// have already been fixed up.
if (Symbol->isInSection()) {
const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
Fragment->getParent()->getSection());
if (Section.hasAttribute(MCSectionMachO::S_ATTR_DEBUG))
Base = 0;
}
// x86_64 almost always uses external relocations, except when there is no
// symbol to use as a base address (a local symbol with no preceeding
// non-local symbol).
if (Base) {
Index = Base->getIndex();
IsExtern = 1;
// Add the local offset, if needed.
if (Base != &SD)
Value += Layout.getSymbolAddress(&SD) - Layout.getSymbolAddress(Base);
} else if (Symbol->isInSection()) {
// The index is the section ordinal (1-based).
Index = SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
Value += Layout.getSymbolAddress(&SD);
if (IsPCRel)
Value -= FixupAddress + (1 << Log2Size);
} else {
report_fatal_error("unsupported relocation of undefined symbol '" +
Symbol->getName() + "'");
}
MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
if (IsPCRel) {
if (IsRIPRel) {
if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
// x86_64 distinguishes movq foo@GOTPCREL so that the linker can
// rewrite the movq to an leaq at link time if the symbol ends up in
// the same linkage unit.
if (unsigned(Fixup.getKind()) == X86::reloc_riprel_4byte_movq_load)
Type = RIT_X86_64_GOTLoad;
else
Type = RIT_X86_64_GOT;
} else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
Type = RIT_X86_64_TLV;
} else if (Modifier != MCSymbolRefExpr::VK_None) {
report_fatal_error("unsupported symbol modifier in relocation");
} else {
Type = RIT_X86_64_Signed;
// The Darwin x86_64 relocation format has a problem where it cannot
// encode an address (L<foo> + <constant>) which is outside the atom
// containing L<foo>. Generally, this shouldn't occur but it does
// happen when we have a RIPrel instruction with data following the
// relocation entry (e.g., movb $012, L0(%rip)). Even with the PCrel
// adjustment Darwin x86_64 uses, the offset is still negative and
// the linker has no way to recognize this.
//
// To work around this, Darwin uses several special relocation types
// to indicate the offsets. However, the specification or
// implementation of these seems to also be incomplete; they should
// adjust the addend as well based on the actual encoded instruction
// (the additional bias), but instead appear to just look at the
// final offset.
switch (-(Target.getConstant() + (1LL << Log2Size))) {
case 1: Type = RIT_X86_64_Signed1; break;
case 2: Type = RIT_X86_64_Signed2; break;
case 4: Type = RIT_X86_64_Signed4; break;
}
}
} else {
if (Modifier != MCSymbolRefExpr::VK_None)
report_fatal_error("unsupported symbol modifier in branch "
"relocation");
Type = RIT_X86_64_Branch;
}
} else {
if (Modifier == MCSymbolRefExpr::VK_GOT) {
Type = RIT_X86_64_GOT;
} else if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
// GOTPCREL is allowed as a modifier on non-PCrel instructions, in
// which case all we do is set the PCrel bit in the relocation entry;
// this is used with exception handling, for example. The source is
// required to include any necessary offset directly.
Type = RIT_X86_64_GOT;
IsPCRel = 1;
} else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
report_fatal_error("TLVP symbol modifier should have been rip-rel");
} else if (Modifier != MCSymbolRefExpr::VK_None)
report_fatal_error("unsupported symbol modifier in relocation");
else
Type = RIT_X86_64_Unsigned;
}
}
// x86_64 always writes custom values into the fixups.
FixedValue = Value;
// struct relocation_info (8 bytes)
MachRelocationEntry MRE;
MRE.Word0 = FixupOffset;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Relocations[Fragment->getParent()].push_back(MRE);
}
void RecordScatteredRelocation(const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
unsigned IsPCRel = isFixupKindPCRel(Fixup.getKind());
unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
unsigned Type = RIT_Vanilla;
// See <reloc.h>.
const MCSymbol *A = &Target.getSymA()->getSymbol();
MCSymbolData *A_SD = &Asm.getSymbolData(*A);
if (!A_SD->getFragment())
report_fatal_error("symbol '" + A->getName() +
"' can not be undefined in a subtraction expression");
uint32_t Value = Layout.getSymbolAddress(A_SD);
uint32_t Value2 = 0;
if (const MCSymbolRefExpr *B = Target.getSymB()) {
MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
if (!B_SD->getFragment())
report_fatal_error("symbol '" + B->getSymbol().getName() +
"' can not be undefined in a subtraction expression");
// Select the appropriate difference relocation type.
//
// Note that there is no longer any semantic difference between these two
// relocation types from the linkers point of view, this is done solely
// for pedantic compatibility with 'as'.
Type = A_SD->isExternal() ? RIT_Difference : RIT_LocalDifference;
Value2 = Layout.getSymbolAddress(B_SD);
}
// Relocations are written out in reverse order, so the PAIR comes first.
if (Type == RIT_Difference || Type == RIT_LocalDifference) {
MachRelocationEntry MRE;
MRE.Word0 = ((0 << 0) |
(RIT_Pair << 24) |
(Log2Size << 28) |
(IsPCRel << 30) |
RF_Scattered);
MRE.Word1 = Value2;
Relocations[Fragment->getParent()].push_back(MRE);
}
MachRelocationEntry MRE;
MRE.Word0 = ((FixupOffset << 0) |
(Type << 24) |
(Log2Size << 28) |
(IsPCRel << 30) |
RF_Scattered);
MRE.Word1 = Value;
Relocations[Fragment->getParent()].push_back(MRE);
}
void RecordTLVPRelocation(const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
assert(Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP &&
!Is64Bit &&
"Should only be called with a 32-bit TLVP relocation!");
unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
uint32_t Value = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
unsigned IsPCRel = 0;
// Get the symbol data.
MCSymbolData *SD_A = &Asm.getSymbolData(Target.getSymA()->getSymbol());
unsigned Index = SD_A->getIndex();
// We're only going to have a second symbol in pic mode and it'll be a
// subtraction from the picbase. For 32-bit pic the addend is the difference
// between the picbase and the next address. For 32-bit static the addend
// is zero.
if (Target.getSymB()) {
// If this is a subtraction then we're pcrel.
uint32_t FixupAddress =
Layout.getFragmentAddress(Fragment) + Fixup.getOffset();
MCSymbolData *SD_B = &Asm.getSymbolData(Target.getSymB()->getSymbol());
IsPCRel = 1;
FixedValue = (FixupAddress - Layout.getSymbolAddress(SD_B) +
Target.getConstant());
FixedValue += 1ULL << Log2Size;
} else {
FixedValue = 0;
}
// struct relocation_info (8 bytes)
MachRelocationEntry MRE;
MRE.Word0 = Value;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(1 << 27) | // Extern
(RIT_TLV << 28)); // Type
Relocations[Fragment->getParent()].push_back(MRE);
}
void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, uint64_t &FixedValue) {
if (Is64Bit) {
RecordX86_64Relocation(Asm, Layout, Fragment, Fixup, Target, FixedValue);
return;
}
unsigned IsPCRel = isFixupKindPCRel(Fixup.getKind());
unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
// If this is a 32-bit TLVP reloc it's handled a bit differently.
if (Target.getSymA() &&
Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP) {
RecordTLVPRelocation(Asm, Layout, Fragment, Fixup, Target, FixedValue);
return;
}
// If this is a difference or a defined symbol plus an offset, then we need
// a scattered relocation entry.
// Differences always require scattered relocations.
if (Target.getSymB())
return RecordScatteredRelocation(Asm, Layout, Fragment, Fixup,
Target, FixedValue);
// Get the symbol data, if any.
MCSymbolData *SD = 0;
if (Target.getSymA())
SD = &Asm.getSymbolData(Target.getSymA()->getSymbol());
// If this is an internal relocation with an offset, it also needs a
// scattered relocation entry.
uint32_t Offset = Target.getConstant();
if (IsPCRel)
Offset += 1 << Log2Size;
if (Offset && SD && !doesSymbolRequireExternRelocation(SD))
return RecordScatteredRelocation(Asm, Layout, Fragment, Fixup,
Target, FixedValue);
// See <reloc.h>.
uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
unsigned Index = 0;
unsigned IsExtern = 0;
unsigned Type = 0;
if (Target.isAbsolute()) { // constant
// SymbolNum of 0 indicates the absolute section.
//
// FIXME: Currently, these are never generated (see code below). I cannot
// find a case where they are actually emitted.
Type = RIT_Vanilla;
} else {
// Check whether we need an external or internal relocation.
if (doesSymbolRequireExternRelocation(SD)) {
IsExtern = 1;
Index = SD->getIndex();
// For external relocations, make sure to offset the fixup value to
// compensate for the addend of the symbol address, if it was
// undefined. This occurs with weak definitions, for example.
if (!SD->Symbol->isUndefined())
FixedValue -= Layout.getSymbolAddress(SD);
} else {
// The index is the section ordinal (1-based).
Index = SD->getFragment()->getParent()->getOrdinal() + 1;
}
Type = RIT_Vanilla;
}
// struct relocation_info (8 bytes)
MachRelocationEntry MRE;
MRE.Word0 = FixupOffset;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Relocations[Fragment->getParent()].push_back(MRE);
}
void BindIndirectSymbols(MCAssembler &Asm) {
// This is the point where 'as' creates actual symbols for indirect symbols
// (in the following two passes). It would be easier for us to do this
// sooner when we see the attribute, but that makes getting the order in the
// symbol table much more complicated than it is worth.
//
// FIXME: Revisit this when the dust settles.
// Bind non lazy symbol pointers first.
unsigned IndirectIndex = 0;
for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
const MCSectionMachO &Section =
cast<MCSectionMachO>(it->SectionData->getSection());
if (Section.getType() != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
continue;
// Initialize the section indirect symbol base, if necessary.
if (!IndirectSymBase.count(it->SectionData))
IndirectSymBase[it->SectionData] = IndirectIndex;
Asm.getOrCreateSymbolData(*it->Symbol);
}
// Then lazy symbol pointers and symbol stubs.
IndirectIndex = 0;
for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
const MCSectionMachO &Section =
cast<MCSectionMachO>(it->SectionData->getSection());
if (Section.getType() != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
Section.getType() != MCSectionMachO::S_SYMBOL_STUBS)
continue;
// Initialize the section indirect symbol base, if necessary.
if (!IndirectSymBase.count(it->SectionData))
IndirectSymBase[it->SectionData] = IndirectIndex;
// Set the symbol type to undefined lazy, but only on construction.
//
// FIXME: Do not hardcode.
bool Created;
MCSymbolData &Entry = Asm.getOrCreateSymbolData(*it->Symbol, &Created);
if (Created)
Entry.setFlags(Entry.getFlags() | 0x0001);
}
}
/// ComputeSymbolTable - Compute the symbol table data
///
/// \param StringTable [out] - The string table data.
/// \param StringIndexMap [out] - Map from symbol names to offsets in the
/// string table.
void ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
std::vector<MachSymbolData> &LocalSymbolData,
std::vector<MachSymbolData> &ExternalSymbolData,
std::vector<MachSymbolData> &UndefinedSymbolData) {
// Build section lookup table.
DenseMap<const MCSection*, uint8_t> SectionIndexMap;
unsigned Index = 1;
for (MCAssembler::iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it, ++Index)
SectionIndexMap[&it->getSection()] = Index;
assert(Index <= 256 && "Too many sections!");
// Index 0 is always the empty string.
StringMap<uint64_t> StringIndexMap;
StringTable += '\x00';
// Build the symbol arrays and the string table, but only for non-local
// symbols.
//
// The particular order that we collect the symbols and create the string
// table, then sort the symbols is chosen to match 'as'. Even though it
// doesn't matter for correctness, this is important for letting us diff .o
// files.
for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
ie = Asm.symbol_end(); it != ie; ++it) {
const MCSymbol &Symbol = it->getSymbol();
// Ignore non-linker visible symbols.
if (!Asm.isSymbolLinkerVisible(it->getSymbol()))
continue;
if (!it->isExternal() && !Symbol.isUndefined())
continue;
uint64_t &Entry = StringIndexMap[Symbol.getName()];
if (!Entry) {
Entry = StringTable.size();
StringTable += Symbol.getName();
StringTable += '\x00';
}
MachSymbolData MSD;
MSD.SymbolData = it;
MSD.StringIndex = Entry;
if (Symbol.isUndefined()) {
MSD.SectionIndex = 0;
UndefinedSymbolData.push_back(MSD);
} else if (Symbol.isAbsolute()) {
MSD.SectionIndex = 0;
ExternalSymbolData.push_back(MSD);
} else {
MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
assert(MSD.SectionIndex && "Invalid section index!");
ExternalSymbolData.push_back(MSD);
}
}
// Now add the data for local symbols.
for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
ie = Asm.symbol_end(); it != ie; ++it) {
const MCSymbol &Symbol = it->getSymbol();
// Ignore non-linker visible symbols.
if (!Asm.isSymbolLinkerVisible(it->getSymbol()))
continue;
if (it->isExternal() || Symbol.isUndefined())
continue;
uint64_t &Entry = StringIndexMap[Symbol.getName()];
if (!Entry) {
Entry = StringTable.size();
StringTable += Symbol.getName();
StringTable += '\x00';
}
MachSymbolData MSD;
MSD.SymbolData = it;
MSD.StringIndex = Entry;
if (Symbol.isAbsolute()) {
MSD.SectionIndex = 0;
LocalSymbolData.push_back(MSD);
} else {
MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
assert(MSD.SectionIndex && "Invalid section index!");
LocalSymbolData.push_back(MSD);
}
}
// External and undefined symbols are required to be in lexicographic order.
std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
// Set the symbol indices.
Index = 0;
for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
LocalSymbolData[i].SymbolData->setIndex(Index++);
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
ExternalSymbolData[i].SymbolData->setIndex(Index++);
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
UndefinedSymbolData[i].SymbolData->setIndex(Index++);
// The string table is padded to a multiple of 4.
while (StringTable.size() % 4)
StringTable += '\x00';
}
void ExecutePostLayoutBinding(MCAssembler &Asm) {
// Create symbol data for any indirect symbols.
BindIndirectSymbols(Asm);
// Compute symbol table information and bind symbol indices.
ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
UndefinedSymbolData);
}
bool IsFixupFullyResolved(const MCAssembler &Asm,
const MCValue Target,
bool IsPCRel,
const MCFragment *DF) const {
// If we are using scattered symbols, determine whether this value is
// actually resolved; scattering may cause atoms to move.
if (Asm.getBackend().hasScatteredSymbols()) {
if (Asm.getBackend().hasReliableSymbolDifference()) {
// If this is a PCrel relocation, find the base atom (identified by its
// symbol) that the fixup value is relative to.
const MCSymbolData *BaseSymbol = 0;
if (IsPCRel) {
BaseSymbol = DF->getAtom();
if (!BaseSymbol)
return false;
}
return isScatteredFixupFullyResolved(Asm, Target, BaseSymbol);
} else {
const MCSection *BaseSection = 0;
if (IsPCRel)
BaseSection = &DF->getParent()->getSection();
return isScatteredFixupFullyResolvedSimple(Asm, Target, BaseSection);
}
}
return true;
}
void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout) {
unsigned NumSections = Asm.size();
// The section data starts after the header, the segment load command (and
// section headers) and the symbol table.
unsigned NumLoadCommands = 1;
uint64_t LoadCommandsSize = Is64Bit ?
SegmentLoadCommand64Size + NumSections * Section64Size :
SegmentLoadCommand32Size + NumSections * Section32Size;
// Add the symbol table load command sizes, if used.
unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
UndefinedSymbolData.size();
if (NumSymbols) {
NumLoadCommands += 2;
LoadCommandsSize += SymtabLoadCommandSize + DysymtabLoadCommandSize;
}
// Compute the total size of the section data, as well as its file size and
// vm size.
uint64_t SectionDataStart = (Is64Bit ? Header64Size : Header32Size)
+ LoadCommandsSize;
uint64_t SectionDataSize = 0;
uint64_t SectionDataFileSize = 0;
uint64_t VMSize = 0;
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionData &SD = *it;
uint64_t Address = Layout.getSectionAddress(&SD);
uint64_t Size = Layout.getSectionSize(&SD);
uint64_t FileSize = Layout.getSectionFileSize(&SD);
VMSize = std::max(VMSize, Address + Size);
if (Asm.getBackend().isVirtualSection(SD.getSection()))
continue;
SectionDataSize = std::max(SectionDataSize, Address + Size);
SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
}
// The section data is padded to 4 bytes.
//
// FIXME: Is this machine dependent?
unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
SectionDataFileSize += SectionDataPadding;
// Write the prolog, starting with the header and load command...
WriteHeader(NumLoadCommands, LoadCommandsSize,
Asm.getSubsectionsViaSymbols());
WriteSegmentLoadCommand(NumSections, VMSize,
SectionDataStart, SectionDataSize);
// ... and then the section headers.
uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
std::vector<MachRelocationEntry> &Relocs = Relocations[it];
unsigned NumRelocs = Relocs.size();
uint64_t SectionStart = SectionDataStart + Layout.getSectionAddress(it);
WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
RelocTableEnd += NumRelocs * RelocationInfoSize;
}
// Write the symbol table load command, if used.
if (NumSymbols) {
unsigned FirstLocalSymbol = 0;
unsigned NumLocalSymbols = LocalSymbolData.size();
unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
unsigned NumExternalSymbols = ExternalSymbolData.size();
unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
unsigned NumSymTabSymbols =
NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
uint64_t IndirectSymbolOffset = 0;
// If used, the indirect symbols are written after the section data.
if (NumIndirectSymbols)
IndirectSymbolOffset = RelocTableEnd;
// The symbol table is written after the indirect symbol data.
uint64_t SymbolTableOffset = RelocTableEnd + IndirectSymbolSize;
// The string table is written after symbol table.
uint64_t StringTableOffset =
SymbolTableOffset + NumSymTabSymbols * (Is64Bit ? Nlist64Size :
Nlist32Size);
WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
StringTableOffset, StringTable.size());
WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
FirstExternalSymbol, NumExternalSymbols,
FirstUndefinedSymbol, NumUndefinedSymbols,
IndirectSymbolOffset, NumIndirectSymbols);
}
// Write the actual section data.
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it)
Asm.WriteSectionData(it, Layout, Writer);
// Write the extra padding.
WriteZeros(SectionDataPadding);
// Write the relocation entries.
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
// Write the section relocation entries, in reverse order to match 'as'
// (approximately, the exact algorithm is more complicated than this).
std::vector<MachRelocationEntry> &Relocs = Relocations[it];
for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
Write32(Relocs[e - i - 1].Word0);
Write32(Relocs[e - i - 1].Word1);
}
}
// Write the symbol table data, if used.
if (NumSymbols) {
// Write the indirect symbol entries.
for (MCAssembler::const_indirect_symbol_iterator
it = Asm.indirect_symbol_begin(),
ie = Asm.indirect_symbol_end(); it != ie; ++it) {
// Indirect symbols in the non lazy symbol pointer section have some
// special handling.
const MCSectionMachO &Section =
static_cast<const MCSectionMachO&>(it->SectionData->getSection());
if (Section.getType() == MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS) {
// If this symbol is defined and internal, mark it as such.
if (it->Symbol->isDefined() &&
!Asm.getSymbolData(*it->Symbol).isExternal()) {
uint32_t Flags = ISF_Local;
if (it->Symbol->isAbsolute())
Flags |= ISF_Absolute;
Write32(Flags);
continue;
}
}
Write32(Asm.getSymbolData(*it->Symbol).getIndex());
}
// FIXME: Check that offsets match computed ones.
// Write the symbol table entries.
for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
WriteNlist(LocalSymbolData[i], Layout);
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
WriteNlist(ExternalSymbolData[i], Layout);
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
WriteNlist(UndefinedSymbolData[i], Layout);
// Write the string table.
OS << StringTable.str();
}
}
};
}
MachObjectWriter::MachObjectWriter(raw_ostream &OS,
bool Is64Bit,
bool IsLittleEndian)
: MCObjectWriter(OS, IsLittleEndian)
{
Impl = new MachObjectWriterImpl(this, Is64Bit);
}
MachObjectWriter::~MachObjectWriter() {
delete (MachObjectWriterImpl*) Impl;
}
void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
((MachObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
}
void MachObjectWriter::RecordRelocation(const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
((MachObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
Target, FixedValue);
}
bool MachObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
const MCValue Target,
bool IsPCRel,
const MCFragment *DF) const {
return ((MachObjectWriterImpl*) Impl)->IsFixupFullyResolved(Asm, Target,
IsPCRel, DF);
}
void MachObjectWriter::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
((MachObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);
}
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