//===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "assembler"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Target/TargetMachOWriterInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <vector>
using namespace llvm;
class MachObjectWriter;
STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
// FIXME FIXME FIXME: There are number of places in this file where we convert
// what is a 64-bit assembler value used for computation into a value in the
// object file, which may truncate it. We should detect that truncation where
// invalid and report errors back.
static void WriteFileData(raw_ostream &OS, const MCSectionData &SD,
MachObjectWriter &MOW);
/// isVirtualSection - Check if this is a section which does not actually exist
/// in the object file.
static bool isVirtualSection(const MCSection &Section) {
// FIXME: Lame.
const MCSectionMachO &SMO = static_cast<const MCSectionMachO&>(Section);
unsigned Type = SMO.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
return (Type == MCSectionMachO::S_ZEROFILL);
}
class MachObjectWriter {
// See <mach-o/loader.h>.
enum {
Header_Magic32 = 0xFEEDFACE,
Header_Magic64 = 0xFEEDFACF
};
static const unsigned Header32Size = 28;
static const unsigned Header64Size = 32;
static const unsigned SegmentLoadCommand32Size = 56;
static const unsigned Section32Size = 68;
static const unsigned SymtabLoadCommandSize = 24;
static const unsigned DysymtabLoadCommandSize = 80;
static const unsigned Nlist32Size = 12;
static const unsigned RelocationInfoSize = 8;
enum HeaderFileType {
HFT_Object = 0x1
};
enum HeaderFlags {
HF_SubsectionsViaSymbols = 0x2000
};
enum LoadCommandType {
LCT_Segment = 0x1,
LCT_Symtab = 0x2,
LCT_Dysymtab = 0xb
};
// 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
};
/// 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();
}
};
raw_ostream &OS;
bool IsLSB;
public:
MachObjectWriter(raw_ostream &_OS, bool _IsLSB = true)
: OS(_OS), IsLSB(_IsLSB) {
}
/// @name Helper Methods
/// @{
void Write8(uint8_t Value) {
OS << char(Value);
}
void Write16(uint16_t Value) {
if (IsLSB) {
Write8(uint8_t(Value >> 0));
Write8(uint8_t(Value >> 8));
} else {
Write8(uint8_t(Value >> 8));
Write8(uint8_t(Value >> 0));
}
}
void Write32(uint32_t Value) {
if (IsLSB) {
Write16(uint16_t(Value >> 0));
Write16(uint16_t(Value >> 16));
} else {
Write16(uint16_t(Value >> 16));
Write16(uint16_t(Value >> 0));
}
}
void Write64(uint64_t Value) {
if (IsLSB) {
Write32(uint32_t(Value >> 0));
Write32(uint32_t(Value >> 32));
} else {
Write32(uint32_t(Value >> 32));
Write32(uint32_t(Value >> 0));
}
}
void WriteZeros(unsigned N) {
const char Zeros[16] = { 0 };
for (unsigned i = 0, e = N / 16; i != e; ++i)
OS << StringRef(Zeros, 16);
OS << StringRef(Zeros, N % 16);
}
void WriteString(StringRef Str, unsigned ZeroFillSize = 0) {
OS << Str;
if (ZeroFillSize)
WriteZeros(ZeroFillSize - Str.size());
}
/// @}
void WriteHeader32(unsigned NumLoadCommands, unsigned LoadCommandsSize,
bool SubsectionsViaSymbols) {
uint32_t Flags = 0;
if (SubsectionsViaSymbols)
Flags |= HF_SubsectionsViaSymbols;
// struct mach_header (28 bytes)
uint64_t Start = OS.tell();
(void) Start;
Write32(Header_Magic32);
// FIXME: Support cputype.
Write32(TargetMachOWriterInfo::HDR_CPU_TYPE_I386);
// FIXME: Support cpusubtype.
Write32(TargetMachOWriterInfo::HDR_CPU_SUBTYPE_I386_ALL);
Write32(HFT_Object);
Write32(NumLoadCommands); // Object files have a single load command, the
// segment.
Write32(LoadCommandsSize);
Write32(Flags);
assert(OS.tell() - Start == Header32Size);
}
/// WriteSegmentLoadCommand32 - Write a 32-bit segment load command.
///
/// \arg NumSections - The number of sections in this segment.
/// \arg SectionDataSize - The total size of the sections.
void WriteSegmentLoadCommand32(unsigned NumSections,
uint64_t VMSize,
uint64_t SectionDataStartOffset,
uint64_t SectionDataSize) {
// struct segment_command (56 bytes)
uint64_t Start = OS.tell();
(void) Start;
Write32(LCT_Segment);
Write32(SegmentLoadCommand32Size + NumSections * Section32Size);
WriteString("", 16);
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 == SegmentLoadCommand32Size);
}
void WriteSection32(const MCSectionData &SD, uint64_t FileOffset,
uint64_t RelocationsStart, unsigned NumRelocations) {
// The offset is unused for virtual sections.
if (isVirtualSection(SD.getSection())) {
assert(SD.getFileSize() == 0 && "Invalid file size!");
FileOffset = 0;
}
// struct section (68 bytes)
uint64_t Start = OS.tell();
(void) Start;
// FIXME: cast<> support!
const MCSectionMachO &Section =
static_cast<const MCSectionMachO&>(SD.getSection());
WriteString(Section.getSectionName(), 16);
WriteString(Section.getSegmentName(), 16);
Write32(SD.getAddress()); // address
Write32(SD.getSize()); // size
Write32(FileOffset);
assert(isPowerOf2_32(SD.getAlignment()) && "Invalid alignment!");
Write32(Log2_32(SD.getAlignment()));
Write32(NumRelocations ? RelocationsStart : 0);
Write32(NumRelocations);
Write32(Section.getTypeAndAttributes());
Write32(0); // reserved1
Write32(Section.getStubSize()); // reserved2
assert(OS.tell() - Start == 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 WriteNlist32(MachSymbolData &MSD) {
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()) {
llvm_unreachable("FIXME: Not yet implemented!");
} else {
Address = Data.getFragment()->getAddress() + Data.getOffset();
}
} 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)
llvm_report_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);
Write32(Address);
}
struct MachRelocationEntry {
uint32_t Word0;
uint32_t Word1;
};
void ComputeScatteredRelocationInfo(MCAssembler &Asm,
MCSectionData::Fixup &Fixup,
const MCValue &Target,
DenseMap<const MCSymbol*,MCSymbolData*> &SymbolMap,
std::vector<MachRelocationEntry> &Relocs) {
uint32_t Address = Fixup.Fragment->getOffset() + Fixup.Offset;
unsigned IsPCRel = 0;
unsigned Type = RIT_Vanilla;
// See <reloc.h>.
const MCSymbol *A = Target.getSymA();
MCSymbolData *SD = SymbolMap.lookup(A);
uint32_t Value = SD->getFragment()->getAddress() + SD->getOffset();
uint32_t Value2 = 0;
if (const MCSymbol *B = Target.getSymB()) {
Type = RIT_LocalDifference;
MCSymbolData *SD = SymbolMap.lookup(B);
Value2 = SD->getFragment()->getAddress() + SD->getOffset();
}
unsigned Log2Size = Log2_32(Fixup.Size);
assert((1U << Log2Size) == Fixup.Size && "Invalid fixup size!");
// The value which goes in the fixup is current value of the expression.
Fixup.FixedValue = Value - Value2 + Target.getConstant();
MachRelocationEntry MRE;
MRE.Word0 = ((Address << 0) |
(Type << 24) |
(Log2Size << 28) |
(IsPCRel << 30) |
RF_Scattered);
MRE.Word1 = Value;
Relocs.push_back(MRE);
if (Type == RIT_LocalDifference) {
Type = RIT_Pair;
MachRelocationEntry MRE;
MRE.Word0 = ((0 << 0) |
(Type << 24) |
(Log2Size << 28) |
(0 << 30) |
RF_Scattered);
MRE.Word1 = Value2;
Relocs.push_back(MRE);
}
}
void ComputeRelocationInfo(MCAssembler &Asm,
MCSectionData::Fixup &Fixup,
DenseMap<const MCSymbol*,MCSymbolData*> &SymbolMap,
std::vector<MachRelocationEntry> &Relocs) {
MCValue Target;
if (!Fixup.Value->EvaluateAsRelocatable(Target))
llvm_report_error("expected relocatable expression");
// If this is a difference or a local symbol plus an offset, then we need a
// scattered relocation entry.
if (Target.getSymB() ||
(Target.getSymA() && !Target.getSymA()->isUndefined() &&
Target.getConstant()))
return ComputeScatteredRelocationInfo(Asm, Fixup, Target,
SymbolMap, Relocs);
// See <reloc.h>.
uint32_t Address = Fixup.Fragment->getOffset() + Fixup.Offset;
uint32_t Value = 0;
unsigned Index = 0;
unsigned IsPCRel = 0;
unsigned IsExtern = 0;
unsigned Type = 0;
if (Target.isAbsolute()) { // constant
// SymbolNum of 0 indicates the absolute section.
Type = RIT_Vanilla;
Value = 0;
llvm_unreachable("FIXME: Not yet implemented!");
} else {
const MCSymbol *Symbol = Target.getSymA();
MCSymbolData *SD = SymbolMap.lookup(Symbol);
if (Symbol->isUndefined()) {
IsExtern = 1;
Index = SD->getIndex();
Value = 0;
} else {
// The index is the section ordinal.
//
// FIXME: O(N)
Index = 1;
for (MCAssembler::iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it, ++Index)
if (&*it == SD->getFragment()->getParent())
break;
Value = SD->getFragment()->getAddress() + SD->getOffset();
}
Type = RIT_Vanilla;
}
// The value which goes in the fixup is current value of the expression.
Fixup.FixedValue = Value + Target.getConstant();
unsigned Log2Size = Log2_32(Fixup.Size);
assert((1U << Log2Size) == Fixup.Size && "Invalid fixup size!");
// struct relocation_info (8 bytes)
MachRelocationEntry MRE;
MRE.Word0 = Address;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Relocs.push_back(MRE);
}
void BindIndirectSymbols(MCAssembler &Asm,
DenseMap<const MCSymbol*,MCSymbolData*> &SymbolMap) {
// 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());
unsigned Type =
Section.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
if (Type != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
continue;
MCSymbolData *&Entry = SymbolMap[it->Symbol];
if (!Entry)
Entry = new MCSymbolData(*it->Symbol, 0, 0, &Asm);
}
// 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());
unsigned Type =
Section.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
if (Type != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
Type != MCSectionMachO::S_SYMBOL_STUBS)
continue;
MCSymbolData *&Entry = SymbolMap[it->Symbol];
if (!Entry) {
Entry = new MCSymbolData(*it->Symbol, 0, 0, &Asm);
// Set the symbol type to undefined lazy, but only on construction.
//
// FIXME: Do not hardcode.
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 assembler temporaries.
if (it->getSymbol().isTemporary())
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 assembler temporaries.
if (it->getSymbol().isTemporary())
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.
//
// FIXME: Check to see if this varies per arch.
while (StringTable.size() % 4)
StringTable += '\x00';
}
void WriteObject(MCAssembler &Asm) {
unsigned NumSections = Asm.size();
// Compute the symbol -> symbol data map.
//
// FIXME: This should not be here.
DenseMap<const MCSymbol*, MCSymbolData *> SymbolMap;
for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
ie = Asm.symbol_end(); it != ie; ++it)
SymbolMap[&it->getSymbol()] = it;
// Create symbol data for any indirect symbols.
BindIndirectSymbols(Asm, SymbolMap);
// Compute symbol table information.
SmallString<256> StringTable;
std::vector<MachSymbolData> LocalSymbolData;
std::vector<MachSymbolData> ExternalSymbolData;
std::vector<MachSymbolData> UndefinedSymbolData;
unsigned NumSymbols = Asm.symbol_size();
// No symbol table command is written if there are no symbols.
if (NumSymbols)
ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
UndefinedSymbolData);
// The section data starts after the header, the segment load command (and
// section headers) and the symbol table.
unsigned NumLoadCommands = 1;
uint64_t LoadCommandsSize =
SegmentLoadCommand32Size + NumSections * Section32Size;
// Add the symbol table load command sizes, if used.
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 = Header32Size + LoadCommandsSize;
uint64_t SectionDataSize = 0;
uint64_t SectionDataFileSize = 0;
uint64_t VMSize = 0;
for (MCAssembler::iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
MCSectionData &SD = *it;
VMSize = std::max(VMSize, SD.getAddress() + SD.getSize());
if (isVirtualSection(SD.getSection()))
continue;
SectionDataSize = std::max(SectionDataSize,
SD.getAddress() + SD.getSize());
SectionDataFileSize = std::max(SectionDataFileSize,
SD.getAddress() + SD.getFileSize());
}
// The section data is passed 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...
WriteHeader32(NumLoadCommands, LoadCommandsSize,
Asm.getSubsectionsViaSymbols());
WriteSegmentLoadCommand32(NumSections, VMSize,
SectionDataStart, SectionDataSize);
// ... and then the section headers.
//
// We also compute the section relocations while we do this. Note that
// compute relocation info will also update the fixup to have the correct
// value; this will be overwrite the appropriate data in the fragment when
// it is written.
std::vector<MachRelocationEntry> RelocInfos;
uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie;
++it) {
MCSectionData &SD = *it;
// The assembler writes relocations in the reverse order they were seen.
//
// FIXME: It is probably more complicated than this.
unsigned NumRelocsStart = RelocInfos.size();
for (unsigned i = 0, e = SD.fixup_size(); i != e; ++i)
ComputeRelocationInfo(Asm, SD.getFixups()[e - i - 1], SymbolMap,
RelocInfos);
unsigned NumRelocs = RelocInfos.size() - NumRelocsStart;
uint64_t SectionStart = SectionDataStart + SD.getAddress();
WriteSection32(SD, 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 * Nlist32Size;
WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
StringTableOffset, StringTable.size());
WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
FirstExternalSymbol, NumExternalSymbols,
FirstUndefinedSymbol, NumUndefinedSymbols,
IndirectSymbolOffset, NumIndirectSymbols);
}
// Write the actual section data.
for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
WriteFileData(OS, *it, *this);
// Write the extra padding.
WriteZeros(SectionDataPadding);
// Write the relocation entries.
for (unsigned i = 0, e = RelocInfos.size(); i != e; ++i) {
Write32(RelocInfos[i].Word0);
Write32(RelocInfos[i].Word1);
}
// Write the symbol table data, if used.
if (NumSymbols) {
// Write the indirect symbol entries.
for (MCAssembler::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());
unsigned Type =
Section.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
if (Type == MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS) {
// If this symbol is defined and internal, mark it as such.
if (it->Symbol->isDefined() &&
!SymbolMap.lookup(it->Symbol)->isExternal()) {
uint32_t Flags = ISF_Local;
if (it->Symbol->isAbsolute())
Flags |= ISF_Absolute;
Write32(Flags);
continue;
}
}
Write32(SymbolMap[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)
WriteNlist32(LocalSymbolData[i]);
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
WriteNlist32(ExternalSymbolData[i]);
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
WriteNlist32(UndefinedSymbolData[i]);
// Write the string table.
OS << StringTable.str();
}
}
};
/* *** */
MCFragment::MCFragment() : Kind(FragmentType(~0)) {
}
MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
: Kind(_Kind),
Parent(_Parent),
FileSize(~UINT64_C(0))
{
if (Parent)
Parent->getFragmentList().push_back(this);
}
MCFragment::~MCFragment() {
}
uint64_t MCFragment::getAddress() const {
assert(getParent() && "Missing Section!");
return getParent()->getAddress() + Offset;
}
/* *** */
MCSectionData::MCSectionData() : Section(0) {}
MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
: Section(&_Section),
Alignment(1),
Address(~UINT64_C(0)),
Size(~UINT64_C(0)),
FileSize(~UINT64_C(0)),
LastFixupLookup(~0)
{
if (A)
A->getSectionList().push_back(this);
}
const MCSectionData::Fixup *
MCSectionData::LookupFixup(const MCFragment *Fragment, uint64_t Offset) const {
// Use a one level cache to turn the common case of accessing the fixups in
// order into O(1) instead of O(N).
unsigned i = LastFixupLookup, Count = Fixups.size(), End = Fixups.size();
if (i >= End)
i = 0;
while (Count--) {
const Fixup &F = Fixups[i];
if (F.Fragment == Fragment && F.Offset == Offset) {
LastFixupLookup = i;
return &F;
}
++i;
if (i == End)
i = 0;
}
return 0;
}
/* *** */
MCSymbolData::MCSymbolData() : Symbol(0) {}
MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
uint64_t _Offset, MCAssembler *A)
: Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
IsExternal(false), IsPrivateExtern(false),
CommonSize(0), CommonAlign(0), Flags(0), Index(0)
{
if (A)
A->getSymbolList().push_back(this);
}
/* *** */
MCAssembler::MCAssembler(MCContext &_Context, raw_ostream &_OS)
: Context(_Context), OS(_OS), SubsectionsViaSymbols(false)
{
}
MCAssembler::~MCAssembler() {
}
void MCAssembler::LayoutSection(MCSectionData &SD) {
uint64_t Address = SD.getAddress();
for (MCSectionData::iterator it = SD.begin(), ie = SD.end(); it != ie; ++it) {
MCFragment &F = *it;
F.setOffset(Address - SD.getAddress());
// Evaluate fragment size.
switch (F.getKind()) {
case MCFragment::FT_Align: {
MCAlignFragment &AF = cast<MCAlignFragment>(F);
uint64_t Size = OffsetToAlignment(Address, AF.getAlignment());
if (Size > AF.getMaxBytesToEmit())
AF.setFileSize(0);
else
AF.setFileSize(Size);
break;
}
case MCFragment::FT_Data:
F.setFileSize(F.getMaxFileSize());
break;
case MCFragment::FT_Fill: {
MCFillFragment &FF = cast<MCFillFragment>(F);
F.setFileSize(F.getMaxFileSize());
MCValue Target;
if (!FF.getValue().EvaluateAsRelocatable(Target))
llvm_report_error("expected relocatable expression");
// If the fill value is constant, thats it.
if (Target.isAbsolute())
break;
// Otherwise, add fixups for the values.
for (uint64_t i = 0, e = FF.getCount(); i != e; ++i) {
MCSectionData::Fixup Fix(F, i * FF.getValueSize(),
FF.getValue(),FF.getValueSize());
SD.getFixups().push_back(Fix);
}
break;
}
case MCFragment::FT_Org: {
MCOrgFragment &OF = cast<MCOrgFragment>(F);
MCValue Target;
if (!OF.getOffset().EvaluateAsRelocatable(Target))
llvm_report_error("expected relocatable expression");
if (!Target.isAbsolute())
llvm_unreachable("FIXME: Not yet implemented!");
uint64_t OrgOffset = Target.getConstant();
uint64_t Offset = Address - SD.getAddress();
// FIXME: We need a way to communicate this error.
if (OrgOffset < Offset)
llvm_report_error("invalid .org offset '" + Twine(OrgOffset) +
"' (at offset '" + Twine(Offset) + "'");
F.setFileSize(OrgOffset - Offset);
break;
}
case MCFragment::FT_ZeroFill: {
MCZeroFillFragment &ZFF = cast<MCZeroFillFragment>(F);
// Align the fragment offset; it is safe to adjust the offset freely since
// this is only in virtual sections.
uint64_t Aligned = RoundUpToAlignment(Address, ZFF.getAlignment());
F.setOffset(Aligned - SD.getAddress());
// FIXME: This is misnamed.
F.setFileSize(ZFF.getSize());
break;
}
}
Address += F.getFileSize();
}
// Set the section sizes.
SD.setSize(Address - SD.getAddress());
if (isVirtualSection(SD.getSection()))
SD.setFileSize(0);
else
SD.setFileSize(Address - SD.getAddress());
}
/// WriteFileData - Write the \arg F data to the output file.
static void WriteFileData(raw_ostream &OS, const MCFragment &F,
MachObjectWriter &MOW) {
uint64_t Start = OS.tell();
(void) Start;
++EmittedFragments;
// FIXME: Embed in fragments instead?
switch (F.getKind()) {
case MCFragment::FT_Align: {
MCAlignFragment &AF = cast<MCAlignFragment>(F);
uint64_t Count = AF.getFileSize() / AF.getValueSize();
// FIXME: This error shouldn't actually occur (the front end should emit
// multiple .align directives to enforce the semantics it wants), but is
// severe enough that we want to report it. How to handle this?
if (Count * AF.getValueSize() != AF.getFileSize())
llvm_report_error("undefined .align directive, value size '" +
Twine(AF.getValueSize()) +
"' is not a divisor of padding size '" +
Twine(AF.getFileSize()) + "'");
for (uint64_t i = 0; i != Count; ++i) {
switch (AF.getValueSize()) {
default:
assert(0 && "Invalid size!");
case 1: MOW.Write8 (uint8_t (AF.getValue())); break;
case 2: MOW.Write16(uint16_t(AF.getValue())); break;
case 4: MOW.Write32(uint32_t(AF.getValue())); break;
case 8: MOW.Write64(uint64_t(AF.getValue())); break;
}
}
break;
}
case MCFragment::FT_Data:
OS << cast<MCDataFragment>(F).getContents().str();
break;
case MCFragment::FT_Fill: {
MCFillFragment &FF = cast<MCFillFragment>(F);
int64_t Value = 0;
MCValue Target;
if (!FF.getValue().EvaluateAsRelocatable(Target))
llvm_report_error("expected relocatable expression");
if (Target.isAbsolute())
Value = Target.getConstant();
for (uint64_t i = 0, e = FF.getCount(); i != e; ++i) {
if (!Target.isAbsolute()) {
// Find the fixup.
//
// FIXME: Find a better way to write in the fixes.
const MCSectionData::Fixup *Fixup =
F.getParent()->LookupFixup(&F, i * FF.getValueSize());
assert(Fixup && "Missing fixup for fill value!");
Value = Fixup->FixedValue;
}
switch (FF.getValueSize()) {
default:
assert(0 && "Invalid size!");
case 1: MOW.Write8 (uint8_t (Value)); break;
case 2: MOW.Write16(uint16_t(Value)); break;
case 4: MOW.Write32(uint32_t(Value)); break;
case 8: MOW.Write64(uint64_t(Value)); break;
}
}
break;
}
case MCFragment::FT_Org: {
MCOrgFragment &OF = cast<MCOrgFragment>(F);
for (uint64_t i = 0, e = OF.getFileSize(); i != e; ++i)
MOW.Write8(uint8_t(OF.getValue()));
break;
}
case MCFragment::FT_ZeroFill: {
assert(0 && "Invalid zero fill fragment in concrete section!");
break;
}
}
assert(OS.tell() - Start == F.getFileSize());
}
/// WriteFileData - Write the \arg SD data to the output file.
static void WriteFileData(raw_ostream &OS, const MCSectionData &SD,
MachObjectWriter &MOW) {
// Ignore virtual sections.
if (isVirtualSection(SD.getSection())) {
assert(SD.getFileSize() == 0);
return;
}
uint64_t Start = OS.tell();
(void) Start;
for (MCSectionData::const_iterator it = SD.begin(),
ie = SD.end(); it != ie; ++it)
WriteFileData(OS, *it, MOW);
// Add section padding.
assert(SD.getFileSize() >= SD.getSize() && "Invalid section sizes!");
MOW.WriteZeros(SD.getFileSize() - SD.getSize());
assert(OS.tell() - Start == SD.getFileSize());
}
void MCAssembler::Finish() {
// Layout the concrete sections and fragments.
uint64_t Address = 0;
MCSectionData *Prev = 0;
for (iterator it = begin(), ie = end(); it != ie; ++it) {
MCSectionData &SD = *it;
// Skip virtual sections.
if (isVirtualSection(SD.getSection()))
continue;
// Align this section if necessary by adding padding bytes to the previous
// section.
if (uint64_t Pad = OffsetToAlignment(Address, it->getAlignment())) {
assert(Prev && "Missing prev section!");
Prev->setFileSize(Prev->getFileSize() + Pad);
Address += Pad;
}
// Layout the section fragments and its size.
SD.setAddress(Address);
LayoutSection(SD);
Address += SD.getFileSize();
Prev = &SD;
}
// Layout the virtual sections.
for (iterator it = begin(), ie = end(); it != ie; ++it) {
MCSectionData &SD = *it;
if (!isVirtualSection(SD.getSection()))
continue;
SD.setAddress(Address);
LayoutSection(SD);
Address += SD.getSize();
}
// Write the object file.
MachObjectWriter MOW(OS);
MOW.WriteObject(*this);
OS.flush();
}