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llvm-mirror/lib/MC/MCAssembler.cpp

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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/MCAsmLayout.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"
#include "llvm/Target/TargetRegistry.h"
#include "llvm/Target/TargetAsmBackend.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);
return (SMO.getType() == 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
};
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
};
/// 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;
unsigned Is64Bit : 1;
unsigned IsLSB : 1;
/// @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;
/// @}
public:
MachObjectWriter(raw_ostream &_OS, bool _Is64Bit, bool _IsLSB = true)
: OS(_OS), Is64Bit(_Is64Bit), 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 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));
WriteString("", 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 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) 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());
WriteString(Section.getSectionName(), 16);
WriteString(Section.getSegmentName(), 16);
if (Is64Bit) {
Write64(SD.getAddress()); // address
Write64(SD.getSize()); // size
} else {
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
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) {
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.getAddress();
}
} 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);
if (Is64Bit)
Write64(Address);
else
Write32(Address);
}
void RecordScatteredRelocation(MCAssembler &Asm, MCFragment &Fragment,
const MCAsmFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
uint32_t Address = Fragment.getOffset() + 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())
llvm_report_error("symbol '" + A->getName() +
"' can not be undefined in a subtraction expression");
uint32_t Value = A_SD->getAddress();
uint32_t Value2 = 0;
if (const MCSymbolRefExpr *B = Target.getSymB()) {
MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
if (!B_SD->getFragment())
llvm_report_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 = B_SD->getAddress();
}
// 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(MCAssembler &Asm, MCDataFragment &Fragment,
const MCAsmFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
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, Fragment, Fixup, Target, FixedValue);
return;
}
// See <reloc.h>.
uint32_t Address = Fragment.getOffset() + 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);
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->getAddress();
}
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) {
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;
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...
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 + it->getAddress();
WriteSection(*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)
WriteFileData(OS, *it, *this);
// 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]);
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
WriteNlist(ExternalSymbolData[i]);
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
WriteNlist(UndefinedSymbolData[i]);
// Write the string table.
OS << StringTable.str();
}
}
void ApplyFixup(const MCAsmFixup &Fixup, MCDataFragment &DF,
uint64_t FixedValue) {
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(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, TargetAsmBackend &_Backend,
raw_ostream &_OS)
: Context(_Context), Backend(_Backend), OS(_OS), SubsectionsViaSymbols(false)
{
}
MCAssembler::~MCAssembler() {
}
static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm,
const MCAsmFixup &Fixup,
const MCDataFragment *DF,
const MCValue Target,
const MCSection *BaseSection) {
// The effective fixup address is
// addr(atom(A)) + offset(A)
// - addr(atom(B)) - offset(B)
// - addr(<base symbol>) + <fixup offset from base symbol>
// and the offsets are not relocatable, so the fixup is fully resolved when
// addr(atom(A)) - addr(atom(B)) - addr(<base symbol>)) == 0.
//
// The simple (Darwin, except on x86_64) way of dealing with this was to
// assume that any reference to a temporary symbol *must* be a temporary
// symbol in the same atom, unless the sections differ. Therefore, any PCrel
// relocation to a temporary symbol (in the same section) is fully
// resolved. This also works in conjunction with absolutized .set, which
// requires the compiler to use .set to absolutize the differences between
// symbols which the compiler knows to be assembly time constants, so we don't
// need to worry about consider symbol differences fully resolved.
// Non-relative fixups are only resolved if constant.
if (!BaseSection)
return Target.isAbsolute();
// Otherwise, relative fixups are only resolved if not a difference and the
// target is a temporary in the same section.
if (Target.isAbsolute() || Target.getSymB())
return false;
const MCSymbol *A = &Target.getSymA()->getSymbol();
if (!A->isTemporary() || !A->isInSection() ||
&A->getSection() != BaseSection)
return false;
return true;
}
static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
const MCAsmFixup &Fixup,
const MCDataFragment *DF,
const MCValue Target,
const MCSymbolData *BaseSymbol) {
// The effective fixup address is
// addr(atom(A)) + offset(A)
// - addr(atom(B)) - offset(B)
// - addr(BaseSymbol) + <fixup offset from base symbol>
// and the offsets are not relocatable, so the fixup is fully resolved when
// addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
//
// Note that "false" is almost always conservatively correct (it means we emit
// a relocation which is unnecessary), except when it would force us to emit a
// relocation which the target cannot encode.
const MCSymbolData *A_Base = 0, *B_Base = 0;
if (const MCSymbolRefExpr *A = Target.getSymA()) {
// Modified symbol references cannot be resolved.
if (A->getKind() != MCSymbolRefExpr::VK_None)
return false;
A_Base = Asm.getAtom(&Asm.getSymbolData(A->getSymbol()));
if (!A_Base)
return false;
}
if (const MCSymbolRefExpr *B = Target.getSymB()) {
// Modified symbol references cannot be resolved.
if (B->getKind() != MCSymbolRefExpr::VK_None)
return false;
B_Base = Asm.getAtom(&Asm.getSymbolData(B->getSymbol()));
if (!B_Base)
return false;
}
// If there is no base, A and B have to be the same atom for this fixup to be
// fully resolved.
if (!BaseSymbol)
return A_Base == B_Base;
// Otherwise, B must be missing and A must be the base.
return !B_Base && BaseSymbol == A_Base;
}
bool MCAssembler::isSymbolLinkerVisible(const MCSymbolData *SD) const {
// Non-temporary labels should always be visible to the linker.
if (!SD->getSymbol().isTemporary())
return true;
// Absolute temporary labels are never visible.
if (!SD->getFragment())
return false;
// Otherwise, check if the section requires symbols even for temporary labels.
return getBackend().doesSectionRequireSymbols(
SD->getFragment()->getParent()->getSection());
}
const MCSymbolData *MCAssembler::getAtomForAddress(const MCSectionData *Section,
uint64_t Address) const {
const MCSymbolData *Best = 0;
for (MCAssembler::const_symbol_iterator it = symbol_begin(),
ie = symbol_end(); it != ie; ++it) {
// Ignore non-linker visible symbols.
if (!isSymbolLinkerVisible(it))
continue;
// Ignore symbols not in the same section.
if (!it->getFragment() || it->getFragment()->getParent() != Section)
continue;
// Otherwise, find the closest symbol preceding this address (ties are
// resolved in favor of the last defined symbol).
if (it->getAddress() <= Address &&
(!Best || it->getAddress() >= Best->getAddress()))
Best = it;
}
return Best;
}
const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
// Linker visible symbols define atoms.
if (isSymbolLinkerVisible(SD))
return SD;
// Absolute and undefined symbols have no defining atom.
if (!SD->getFragment())
return 0;
// Otherwise, search by address.
return getAtomForAddress(SD->getFragment()->getParent(), SD->getAddress());
}
bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout, MCAsmFixup &Fixup,
MCDataFragment *DF,
MCValue &Target, uint64_t &Value) const {
if (!Fixup.Value->EvaluateAsRelocatable(Target, &Layout))
llvm_report_error("expected relocatable expression");
// FIXME: How do non-scattered symbols work in ELF? I presume the linker
// doesn't support small relocations, but then under what criteria does the
// assembler allow symbol differences?
Value = Target.getConstant();
bool IsResolved = true, IsPCRel = isFixupKindPCRel(Fixup.Kind);
if (const MCSymbolRefExpr *A = Target.getSymA()) {
if (A->getSymbol().isDefined())
Value += getSymbolData(A->getSymbol()).getAddress();
else
IsResolved = false;
}
if (const MCSymbolRefExpr *B = Target.getSymB()) {
if (B->getSymbol().isDefined())
Value -= getSymbolData(B->getSymbol()).getAddress();
else
IsResolved = false;
}
// If we are using scattered symbols, determine whether this value is actually
// resolved; scattering may cause atoms to move.
if (IsResolved && getBackend().hasScatteredSymbols()) {
if (getBackend().hasReliableSymbolDifference()) {
// If this is a PCrel relocation, find the base atom (identified by its
// symbol) that the fixup value is relative to.
const MCSymbolData *BaseSymbol = 0;
if (IsPCRel) {
BaseSymbol = getAtomForAddress(
DF->getParent(), DF->getAddress() + Fixup.Offset);
if (!BaseSymbol)
IsResolved = false;
}
if (IsResolved)
IsResolved = isScatteredFixupFullyResolved(*this, Fixup, DF, Target,
BaseSymbol);
} else {
const MCSection *BaseSection = 0;
if (IsPCRel)
BaseSection = &DF->getParent()->getSection();
IsResolved = isScatteredFixupFullyResolvedSimple(*this, Fixup, DF, Target,
BaseSection);
}
}
if (IsPCRel)
Value -= DF->getAddress() + Fixup.Offset;
return IsResolved;
}
void MCAssembler::LayoutSection(MCSectionData &SD) {
MCAsmLayout Layout(*this);
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);
int64_t TargetLocation;
if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, &Layout))
llvm_report_error("expected assembly-time absolute expression");
// FIXME: We need a way to communicate this error.
int64_t Offset = TargetLocation - F.getOffset();
if (Offset < 0)
llvm_report_error("invalid .org offset '" + Twine(TargetLocation) +
"' (at offset '" + Twine(F.getOffset()) + "'");
F.setFileSize(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.
Address = RoundUpToAlignment(Address, ZFF.getAlignment());
F.setOffset(Address - 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: {
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 until everything fits.
while (LayoutOnce())
continue;
DEBUG_WITH_TYPE("mc-dump", {
llvm::errs() << "assembler backend - post-layout\n--\n";
dump(); });
// FIXME: Factor out MCObjectWriter.
bool Is64Bit = StringRef(getBackend().getTarget().getName()) == "x86-64";
MachObjectWriter MOW(OS, Is64Bit);
// Allow the object writer a chance to perform post-layout binding (for
// example, to set the index fields in the symbol data).
MOW.ExecutePostLayoutBinding(*this);
// Evaluate and apply the fixups, generating relocation entries as necessary.
MCAsmLayout Layout(*this);
for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
for (MCSectionData::iterator it2 = it->begin(),
ie2 = it->end(); it2 != ie2; ++it2) {
MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
if (!DF)
continue;
for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
MCAsmFixup &Fixup = *it3;
// Evaluate the fixup.
MCValue Target;
uint64_t FixedValue;
if (!EvaluateFixup(Layout, Fixup, DF, Target, FixedValue)) {
// The fixup was unresolved, we need a relocation. Inform the object
// writer of the relocation, and give it an opportunity to adjust the
// fixup value if need be.
MOW.RecordRelocation(*this, *DF, Fixup, Target, FixedValue);
}
MOW.ApplyFixup(Fixup, *DF, FixedValue);
}
}
}
// Write the object file.
MOW.WriteObject(*this);
OS.flush();
}
bool MCAssembler::FixupNeedsRelaxation(MCAsmFixup &Fixup, MCDataFragment *DF) {
// FIXME: Share layout object.
MCAsmLayout Layout(*this);
// Currently we only need to relax X86::reloc_pcrel_1byte.
if (unsigned(Fixup.Kind) != X86::reloc_pcrel_1byte)
return false;
// If we cannot resolve the fixup value, it requires relaxation.
MCValue Target;
uint64_t Value;
if (!EvaluateFixup(Layout, Fixup, DF, Target, Value))
return true;
// Otherwise, relax if the value is too big for a (signed) i8.
return int64_t(Value) != int64_t(int8_t(Value));
}
bool MCAssembler::LayoutOnce() {
// 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;
// Align this section if necessary by adding padding bytes to the previous
// section.
if (uint64_t Pad = OffsetToAlignment(Address, it->getAlignment()))
Address += Pad;
SD.setAddress(Address);
LayoutSection(SD);
Address += SD.getSize();
}
// Scan the fixups in order and relax any that don't fit.
for (iterator it = begin(), ie = end(); it != ie; ++it) {
MCSectionData &SD = *it;
for (MCSectionData::iterator it2 = SD.begin(),
ie2 = SD.end(); it2 != ie2; ++it2) {
MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
if (!DF)
continue;
for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
MCAsmFixup &Fixup = *it3;
// Check whether we need to relax this fixup.
if (!FixupNeedsRelaxation(Fixup, DF))
continue;
// Relax the instruction.
//
// FIXME: This is a huge temporary hack which just looks for x86
// branches; the only thing we need to relax on x86 is
// 'X86::reloc_pcrel_1byte'. Once we have MCInst fragments, this will be
// replaced by a TargetAsmBackend hook (most likely tblgen'd) to relax
// an individual MCInst.
SmallVectorImpl<char> &C = DF->getContents();
uint64_t PrevOffset = Fixup.Offset;
unsigned Amt = 0;
// jcc instructions
if (unsigned(C[Fixup.Offset-1]) >= 0x70 &&
unsigned(C[Fixup.Offset-1]) <= 0x7f) {
C[Fixup.Offset] = C[Fixup.Offset-1] + 0x10;
C[Fixup.Offset-1] = char(0x0f);
++Fixup.Offset;
Amt = 4;
// jmp rel8
} else if (C[Fixup.Offset-1] == char(0xeb)) {
C[Fixup.Offset-1] = char(0xe9);
Amt = 3;
} else
llvm_unreachable("unknown 1 byte pcrel instruction!");
Fixup.Value = MCBinaryExpr::Create(
MCBinaryExpr::Sub, Fixup.Value,
MCConstantExpr::Create(3, getContext()),
getContext());
C.insert(C.begin() + Fixup.Offset, Amt, char(0));
Fixup.Kind = MCFixupKind(X86::reloc_pcrel_4byte);
// Update the remaining fixups, which have slid.
//
// FIXME: This is bad for performance, but will be eliminated by the
// move to MCInst specific fragments.
++it3;
for (; it3 != ie3; ++it3)
it3->Offset += Amt;
// Update all the symbols for this fragment, which may have slid.
//
// FIXME: This is really really bad for performance, but will be
// eliminated by the move to MCInst specific fragments.
for (MCAssembler::symbol_iterator it = symbol_begin(),
ie = symbol_end(); it != ie; ++it) {
MCSymbolData &SD = *it;
if (it->getFragment() != DF)
continue;
if (SD.getOffset() > PrevOffset)
SD.setOffset(SD.getOffset() + Amt);
}
// Restart layout.
//
// FIXME: This is O(N^2), but will be eliminated once we have a smart
// MCAsmLayout object.
return true;
}
}
}
return false;
}
// 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:[\n ";
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:[\n ";
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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