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a6eeb6e226
llvm/lib/MC/MachObjectWriter.cpp
Kevin Enderby a6eeb6e226 Fix i386 relocations to Weak Definitions. The relocation entries should be 
external and the item to be relocated should not have the address of the
symbol added in.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103302 91177308-0d34-0410-b5e6-96231b3b80d8
2010-05-07 21:44:23 +00:00

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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;
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 FK_Data_2: return 1;
case X86::reloc_pcrel_4byte:
case X86::reloc_riprel_4byte:
case X86::reloc_riprel_4byte_movq_load:
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_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;
}
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
};
/// 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
};
/// 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 {
const std::string &Name = SymbolData->getSymbol().getName();
return Name < RHS.SymbolData->getSymbol().getName();
}
};
/// @name Relocation Data
/// @{
struct MachRelocationEntry {
uint32_t Word0;
uint32_t Word1;
};
llvm::DenseMap<const MCSectionData*,
std::vector<MachRelocationEntry> > Relocations;
/// @}
/// @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;
// FIXME: cast<> support!
const MCSectionMachO &Section =
static_cast<const 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(0); // 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 MCAsmFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
unsigned IsRIPRel = isFixupKindRIPRel(Fixup.Kind);
unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
// See <reloc.h>.
uint32_t Address = Layout.getFragmentOffset(Fragment) + Fixup.Offset;
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(Layout, &A_SD);
const MCSymbol *B = &Target.getSymB()->getSymbol();
MCSymbolData &B_SD = Asm.getSymbolData(*B);
const MCSymbolData *B_Base = Asm.getAtom(Layout, &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");
// We don't currently support any situation where one or both of the
// symbols would require a local relocation. This is almost certainly
// unused and may not be possible to encode correctly.
if (!A_Base || !B_Base)
report_fatal_error("unsupported local relocations in difference");
// Darwin 'as' doesn't emit correct relocations for this (it ends up with
// a single SIGNED relocation); reject it for now.
if (A_Base == B_Base)
report_fatal_error("unsupported relocation with identical base");
Value += Layout.getSymbolAddress(&A_SD) - Layout.getSymbolAddress(A_Base);
Value -= Layout.getSymbolAddress(&B_SD) - Layout.getSymbolAddress(B_Base);
Index = A_Base->getIndex();
IsExtern = 1;
Type = RIT_X86_64_Unsigned;
MachRelocationEntry MRE;
MRE.Word0 = Address;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Relocations[Fragment->getParent()].push_back(MRE);
Index = B_Base->getIndex();
IsExtern = 1;
Type = RIT_X86_64_Subtractor;
} else {
const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
MCSymbolData &SD = Asm.getSymbolData(*Symbol);
const MCSymbolData *Base = Asm.getAtom(Layout, &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 {
// The index is the section ordinal (1-based).
Index = SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
Value += Layout.getSymbolAddress(&SD);
if (IsPCRel)
Value -= Address + (1 << Log2Size);
}
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.Kind) == X86::reloc_riprel_4byte_movq_load)
Type = RIT_X86_64_GOTLoad;
else
Type = RIT_X86_64_GOT;
} else if (Modifier != MCSymbolRefExpr::VK_None)
report_fatal_error("unsupported symbol modifier in relocation");
else
Type = RIT_X86_64_Signed;
} else {
if (Modifier != MCSymbolRefExpr::VK_None)
report_fatal_error("unsupported symbol modifier in branch "
"relocation");
Type = RIT_X86_64_Branch;
}
// 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.
if (IsRIPRel) {
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_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_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 = Address;
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 MCAsmFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
uint32_t Address = Layout.getFragmentOffset(Fragment) + Fixup.Offset;
unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
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 = ((Address << 0) |
(Type << 24) |
(Log2Size << 28) |
(IsPCRel << 30) |
RF_Scattered);
MRE.Word1 = Value;
Relocations[Fragment->getParent()].push_back(MRE);
}
void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCAsmFixup &Fixup,
MCValue Target, uint64_t &FixedValue) {
if (Is64Bit) {
RecordX86_64Relocation(Asm, Layout, Fragment, Fixup, Target, FixedValue);
return;
}
unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
// If this is a difference or a defined symbol plus an offset, then we need
// a scattered relocation entry.
uint32_t Offset = Target.getConstant();
if (IsPCRel)
Offset += 1 << Log2Size;
if (Target.getSymB() ||
(Target.getSymA() && !Target.getSymA()->getSymbol().isUndefined() &&
Offset)) {
RecordScatteredRelocation(Asm, Layout, Fragment, Fixup,Target,FixedValue);
return;
}
// See <reloc.h>.
uint32_t Address = Layout.getFragmentOffset(Fragment) + Fixup.Offset;
uint32_t Value = 0;
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;
Value = 0;
} else {
const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
MCSymbolData *SD = &Asm.getSymbolData(*Symbol);
// Both references to undefined symbols and references to Weak Definitions
// get external relocation entries. This is so the static and then the
// the dynamic linker can resolve them to the actual definition that will
// be used. And in the case of Weak Definitions a reference to one will
// not always be to the definition in the same object file.
if (Symbol->isUndefined() || (SD->getFlags() & SF_WeakDefinition)) {
IsExtern = 1;
Index = SD->getIndex();
// In the case of a Weak Definition the FixedValue needs to be set to
// to not have the address of the symbol. In the case of an undefined
// symbol you can't call getSymbolAddress().
if (SD->getFlags() & SF_WeakDefinition)
FixedValue -= Layout.getSymbolAddress(SD);
Value = 0;
} else {
// The index is the section ordinal (1-based).
Index = SD->getFragment()->getParent()->getOrdinal() + 1;
Value = Layout.getSymbolAddress(SD);
}
Type = RIT_Vanilla;
}
// struct relocation_info (8 bytes)
MachRelocationEntry MRE;
MRE.Word0 = Address;
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.
for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
ie = Asm.indirect_symbol_end(); it != ie; ++it) {
// FIXME: cast<> support!
const MCSectionMachO &Section =
static_cast<const MCSectionMachO&>(it->SectionData->getSection());
if (Section.getType() != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
continue;
Asm.getOrCreateSymbolData(*it->Symbol);
}
// Then lazy symbol pointers and symbol stubs.
for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
ie = Asm.indirect_symbol_end(); it != ie; ++it) {
// FIXME: cast<> support!
const MCSectionMachO &Section =
static_cast<const MCSectionMachO&>(it->SectionData->getSection());
if (Section.getType() != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
Section.getType() != MCSectionMachO::S_SYMBOL_STUBS)
continue;
// 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))
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))
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);
}
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 MCAsmFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
((MachObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
Target, FixedValue);
}
void MachObjectWriter::WriteObject(const MCAssembler &Asm,
const MCAsmLayout &Layout) {
((MachObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);
}
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