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llvm/lib/MC/MCAssembler.cpp
Kevin Enderby 76687083a5 This is the second patch to allow x86 code to be aligned with optimal nops. 
With the compiler changed to use EmitCodeAlignment() it does change the
functionality.  But X86 assembly code assembled with llvm-mc does not change
its output.  For that we will eventually change the assembler frontend to
detect a '.align x, 0x90' when used in a section that 'hasInstructions' and use
EmitCodeAlignment, but will wait until we have better target hooks.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96988 91177308-0d34-0410-b5e6-96231b3b80d8
2010-02-23 21:41:24 +00:00

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//===- 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/ADT/DenseMap.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MachO.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/Debug.h"
// FIXME: Gross.
#include "../Target/X86/X86FixupKinds.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);
static uint64_t WriteNopData(uint64_t Count, 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);
}
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 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:
return true;
}
}
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(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);
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);
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
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, MCFragment &Fragment,
MCAsmFixup &Fixup,
const MCValue &Target,
DenseMap<const MCSymbol*,MCSymbolData*> &SymbolMap,
std::vector<MachRelocationEntry> &Relocs) {
uint32_t Address = Fragment.getOffset() + Fixup.Offset;
unsigned IsPCRel = 0;
unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
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();
}
// The value which goes in the fixup is current value of the expression.
Fixup.FixedValue = Value - Value2 + Target.getConstant();
if (isFixupKindPCRel(Fixup.Kind)) {
Fixup.FixedValue -= Address;
IsPCRel = 1;
}
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, MCDataFragment &Fragment,
MCAsmFixup &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, Fragment, Fixup, Target,
SymbolMap, Relocs);
// See <reloc.h>.
uint32_t Address = Fragment.getOffset() + Fixup.Offset;
uint32_t Value = 0;
unsigned Index = 0;
unsigned IsPCRel = 0;
unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
unsigned IsExtern = 0;
unsigned Type = 0;
if (Target.isAbsolute()) { // constant
// SymbolNum of 0 indicates the absolute section.
//
// FIXME: When is this generated?
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;
MCAssembler::iterator it = Asm.begin(), ie = Asm.end();
for (; it != ie; ++it, ++Index)
if (&*it == SD->getFragment()->getParent())
break;
assert(it != ie && "Unable to find section index!");
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();
if (isFixupKindPCRel(Fixup.Kind)) {
Fixup.FixedValue -= Address;
IsPCRel = 1;
}
// 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.
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 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...
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
// computing relocation info will also update the fixup to have the correct
// value; this will 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 (MCSectionData::reverse_iterator it2 = SD.rbegin(),
ie2 = SD.rend(); it2 != ie2; ++it2)
if (MCDataFragment *DF = dyn_cast<MCDataFragment>(&*it2))
for (unsigned i = 0, e = DF->fixup_size(); i != e; ++i)
ComputeRelocationInfo(Asm, *DF, DF->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();
}
}
void ApplyFixup(const MCAsmFixup &Fixup, MCDataFragment &DF) {
unsigned Size = 1 << getFixupKindLog2Size(Fixup.Kind);
// FIXME: Endianness assumption.
assert(Fixup.Offset + Size <= DF.getContents().size() &&
"Invalid fixup offset!");
for (unsigned i = 0; i != Size; ++i)
DF.getContents()[Fixup.Offset + i] = uint8_t(Fixup.FixedValue >> (i * 8));
}
};
/* *** */
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)),
HasInstructions(false)
{
if (A)
A->getSectionList().push_back(this);
}
/* *** */
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:
case MCFragment::FT_Fill:
F.setFileSize(F.getMaxFileSize());
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());
}
/// WriteNopData - Write optimal nops to the output file for the \arg Count
/// bytes. This returns the number of bytes written. It may return 0 if
/// the \arg Count is more than the maximum optimal nops.
///
/// FIXME this is X86 32-bit specific and should move to a better place.
static uint64_t WriteNopData(uint64_t Count, MachObjectWriter &MOW) {
static const uint8_t Nops[16][16] = {
// nop
{0x90},
// xchg %ax,%ax
{0x66, 0x90},
// nopl (%[re]ax)
{0x0f, 0x1f, 0x00},
// nopl 0(%[re]ax)
{0x0f, 0x1f, 0x40, 0x00},
// nopl 0(%[re]ax,%[re]ax,1)
{0x0f, 0x1f, 0x44, 0x00, 0x00},
// nopw 0(%[re]ax,%[re]ax,1)
{0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
// nopl 0L(%[re]ax)
{0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
// nopl 0L(%[re]ax,%[re]ax,1)
{0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
// nopw 0L(%[re]ax,%[re]ax,1)
{0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
// nopw %cs:0L(%[re]ax,%[re]ax,1)
{0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
// nopl 0(%[re]ax,%[re]ax,1)
// nopw 0(%[re]ax,%[re]ax,1)
{0x0f, 0x1f, 0x44, 0x00, 0x00,
0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
// nopw 0(%[re]ax,%[re]ax,1)
// nopw 0(%[re]ax,%[re]ax,1)
{0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
// nopw 0(%[re]ax,%[re]ax,1)
// nopl 0L(%[re]ax) */
{0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
// nopl 0L(%[re]ax)
// nopl 0L(%[re]ax)
{0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
// nopl 0L(%[re]ax)
// nopl 0L(%[re]ax,%[re]ax,1)
{0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}
};
if (Count > 15)
return 0;
for (uint64_t i = 0; i < Count; i++)
MOW.Write8 (uint8_t(Nops[Count - 1][i]));
return Count;
}
/// 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()) + "'");
// See if we are aligning with nops, and if so do that first to try to fill
// the Count bytes. Then if that did not fill any bytes or there are any
// bytes left to fill use the the Value and ValueSize to fill the rest.
if (AF.getEmitNops()) {
uint64_t NopByteCount = WriteNopData(Count, MOW);
Count -= NopByteCount;
}
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: {
MCDataFragment &DF = cast<MCDataFragment>(F);
// Apply the fixups.
//
// FIXME: Move elsewhere.
for (MCDataFragment::const_fixup_iterator it = DF.fixup_begin(),
ie = DF.fixup_end(); it != ie; ++it)
MOW.ApplyFixup(*it, DF);
OS << cast<MCDataFragment>(F).getContents().str();
break;
}
case MCFragment::FT_Fill: {
MCFillFragment &FF = cast<MCFillFragment>(F);
for (uint64_t i = 0, e = FF.getCount(); i != e; ++i) {
switch (FF.getValueSize()) {
default:
assert(0 && "Invalid size!");
case 1: MOW.Write8 (uint8_t (FF.getValue())); break;
case 2: MOW.Write16(uint16_t(FF.getValue())); break;
case 4: MOW.Write32(uint32_t(FF.getValue())); break;
case 8: MOW.Write64(uint64_t(FF.getValue())); 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() {
DEBUG_WITH_TYPE("mc-dump", {
llvm::errs() << "assembler backend - pre-layout\n--\n";
dump(); });
// 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();
}
DEBUG_WITH_TYPE("mc-dump", {
llvm::errs() << "assembler backend - post-layout\n--\n";
dump(); });
// Write the object file.
MachObjectWriter MOW(OS);
MOW.WriteObject(*this);
OS.flush();
}
// Debugging methods
namespace llvm {
raw_ostream &operator<<(raw_ostream &OS, const MCAsmFixup &AF) {
OS << "<MCAsmFixup" << " Offset:" << AF.Offset << " Value:" << *AF.Value
<< " Kind:" << AF.Kind << ">";
return OS;
}
}
void MCFragment::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCFragment " << (void*) this << " Offset:" << Offset
<< " FileSize:" << FileSize;
OS << ">";
}
void MCAlignFragment::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCAlignFragment ";
this->MCFragment::dump();
OS << "\n ";
OS << " Alignment:" << getAlignment()
<< " Value:" << getValue() << " ValueSize:" << getValueSize()
<< " MaxBytesToEmit:" << getMaxBytesToEmit() << ">";
}
void MCDataFragment::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCDataFragment ";
this->MCFragment::dump();
OS << "\n ";
OS << " Contents:[";
for (unsigned i = 0, e = getContents().size(); i != e; ++i) {
if (i) OS << ",";
OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
}
OS << "] (" << getContents().size() << " bytes)";
if (!getFixups().empty()) {
OS << ",\n ";
OS << " Fixups:[";
for (fixup_iterator it = fixup_begin(), ie = fixup_end(); it != ie; ++it) {
if (it != fixup_begin()) OS << ",\n ";
OS << *it;
}
OS << "]";
}
OS << ">";
}
void MCFillFragment::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCFillFragment ";
this->MCFragment::dump();
OS << "\n ";
OS << " Value:" << getValue() << " ValueSize:" << getValueSize()
<< " Count:" << getCount() << ">";
}
void MCOrgFragment::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCOrgFragment ";
this->MCFragment::dump();
OS << "\n ";
OS << " Offset:" << getOffset() << " Value:" << getValue() << ">";
}
void MCZeroFillFragment::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCZeroFillFragment ";
this->MCFragment::dump();
OS << "\n ";
OS << " Size:" << getSize() << " Alignment:" << getAlignment() << ">";
}
void MCSectionData::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCSectionData";
OS << " Alignment:" << getAlignment() << " Address:" << Address
<< " Size:" << Size << " FileSize:" << FileSize
<< " Fragments:[";
for (iterator it = begin(), ie = end(); it != ie; ++it) {
if (it != begin()) OS << ",\n ";
it->dump();
}
OS << "]>";
}
void MCSymbolData::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCSymbolData Symbol:" << getSymbol()
<< " Fragment:" << getFragment() << " Offset:" << getOffset()
<< " Flags:" << getFlags() << " Index:" << getIndex();
if (isCommon())
OS << " (common, size:" << getCommonSize()
<< " align: " << getCommonAlignment() << ")";
if (isExternal())
OS << " (external)";
if (isPrivateExtern())
OS << " (private extern)";
OS << ">";
}
void MCAssembler::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCAssembler\n";
OS << " Sections:[";
for (iterator it = begin(), ie = end(); it != ie; ++it) {
if (it != begin()) OS << ",\n ";
it->dump();
}
OS << "],\n";
OS << " Symbols:[";
for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
if (it != symbol_begin()) OS << ",\n ";
it->dump();
}
OS << "]>\n";
}
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