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119c41482e
llvm-mirror/lib/MC/MachObjectWriter.cpp
Rafael Espindola c0ce1c5675 Misc improvements to StringTableBuilder. 
This patch adds write methods to StringTableBuilder so that it is
easier to change the underlying implementation.

Using the write methods, avoid creating a temporary buffer when using
mmaped output.

It also uses a more compact key in the DenseMap. Overall this produces
a slightly faster lld:

firefox
  master 6.853419709
  patch  6.841968912 1.00167361138x faster
chromium
  master 4.297280174
  patch  4.298712163 1.00033323147x slower
chromium fast
  master 1.802335952
  patch  1.806872459 1.00251701521x slower
the gold plugin
  master 0.3247149
  patch  0.321971644 1.00852017888x faster
clang
  master 0.551279945
  patch  0.543733194 1.01387951128x faster
llvm-as
  master 0.032743458
  patch  0.032143478 1.01866568391x faster
the gold plugin fsds
  master 0.350814247
  patch  0.348571741 1.00643341309x faster
clang fsds
  master 0.6281672
  patch  0.621130222 1.01132931187x faster
llvm-as fsds
  master 0.030168899
  patch  0.029797155 1.01247582194x faster
scylla
  master 3.104222518
  patch  3.059590248 1.01458766252x faster

llvm-svn: 283266
2016-10-04 22:43:25 +00:00

989 lines
35 KiB
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Raw Blame History

//===- lib/MC/MachObjectWriter.cpp - Mach-O File Writer -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCMachObjectWriter.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSymbolMachO.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MachO.h"
#include "llvm/Support/raw_ostream.h"
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "mc"
void MachObjectWriter::reset() {
Relocations.clear();
IndirectSymBase.clear();
StringTable.clear();
LocalSymbolData.clear();
ExternalSymbolData.clear();
UndefinedSymbolData.clear();
MCObjectWriter::reset();
}
bool MachObjectWriter::doesSymbolRequireExternRelocation(const MCSymbol &S) {
// Undefined symbols are always extern.
if (S.isUndefined())
return true;
// References to weak definitions require external relocation entries; the
// definition may not always be the one in the same object file.
if (cast<MCSymbolMachO>(S).isWeakDefinition())
return true;
// Otherwise, we can use an internal relocation.
return false;
}
bool MachObjectWriter::
MachSymbolData::operator<(const MachSymbolData &RHS) const {
return Symbol->getName() < RHS.Symbol->getName();
}
bool MachObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
const MCFixupKindInfo &FKI = Asm.getBackend().getFixupKindInfo(
(MCFixupKind) Kind);
return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
}
uint64_t MachObjectWriter::getFragmentAddress(const MCFragment *Fragment,
const MCAsmLayout &Layout) const {
return getSectionAddress(Fragment->getParent()) +
Layout.getFragmentOffset(Fragment);
}
uint64_t MachObjectWriter::getSymbolAddress(const MCSymbol &S,
const MCAsmLayout &Layout) const {
// If this is a variable, then recursively evaluate now.
if (S.isVariable()) {
if (const MCConstantExpr *C =
dyn_cast<const MCConstantExpr>(S.getVariableValue()))
return C->getValue();
MCValue Target;
if (!S.getVariableValue()->evaluateAsRelocatable(Target, &Layout, nullptr))
report_fatal_error("unable to evaluate offset for variable '" +
S.getName() + "'");
// Verify that any used symbols are defined.
if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
report_fatal_error("unable to evaluate offset to undefined symbol '" +
Target.getSymA()->getSymbol().getName() + "'");
if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
report_fatal_error("unable to evaluate offset to undefined symbol '" +
Target.getSymB()->getSymbol().getName() + "'");
uint64_t Address = Target.getConstant();
if (Target.getSymA())
Address += getSymbolAddress(Target.getSymA()->getSymbol(), Layout);
if (Target.getSymB())
Address += getSymbolAddress(Target.getSymB()->getSymbol(), Layout);
return Address;
}
return getSectionAddress(S.getFragment()->getParent()) +
Layout.getSymbolOffset(S);
}
uint64_t MachObjectWriter::getPaddingSize(const MCSection *Sec,
const MCAsmLayout &Layout) const {
uint64_t EndAddr = getSectionAddress(Sec) + Layout.getSectionAddressSize(Sec);
unsigned Next = Sec->getLayoutOrder() + 1;
if (Next >= Layout.getSectionOrder().size())
return 0;
const MCSection &NextSec = *Layout.getSectionOrder()[Next];
if (NextSec.isVirtualSection())
return 0;
return OffsetToAlignment(EndAddr, NextSec.getAlignment());
}
void MachObjectWriter::writeHeader(MachO::HeaderFileType Type,
unsigned NumLoadCommands,
unsigned LoadCommandsSize,
bool SubsectionsViaSymbols) {
uint32_t Flags = 0;
if (SubsectionsViaSymbols)
Flags |= MachO::MH_SUBSECTIONS_VIA_SYMBOLS;
// struct mach_header (28 bytes) or
// struct mach_header_64 (32 bytes)
uint64_t Start = getStream().tell();
(void) Start;
write32(is64Bit() ? MachO::MH_MAGIC_64 : MachO::MH_MAGIC);
write32(TargetObjectWriter->getCPUType());
write32(TargetObjectWriter->getCPUSubtype());
write32(Type);
write32(NumLoadCommands);
write32(LoadCommandsSize);
write32(Flags);
if (is64Bit())
write32(0); // reserved
assert(
getStream().tell() - Start ==
(is64Bit() ? sizeof(MachO::mach_header_64) : sizeof(MachO::mach_header)));
}
/// writeSegmentLoadCommand - Write a segment load command.
///
/// \param NumSections The number of sections in this segment.
/// \param SectionDataSize The total size of the sections.
void MachObjectWriter::writeSegmentLoadCommand(
StringRef Name, unsigned NumSections, uint64_t VMAddr, uint64_t VMSize,
uint64_t SectionDataStartOffset, uint64_t SectionDataSize, uint32_t MaxProt,
uint32_t InitProt) {
// struct segment_command (56 bytes) or
// struct segment_command_64 (72 bytes)
uint64_t Start = getStream().tell();
(void) Start;
unsigned SegmentLoadCommandSize =
is64Bit() ? sizeof(MachO::segment_command_64):
sizeof(MachO::segment_command);
write32(is64Bit() ? MachO::LC_SEGMENT_64 : MachO::LC_SEGMENT);
write32(SegmentLoadCommandSize +
NumSections * (is64Bit() ? sizeof(MachO::section_64) :
sizeof(MachO::section)));
assert(Name.size() <= 16);
writeBytes(Name, 16);
if (is64Bit()) {
write64(VMAddr); // vmaddr
write64(VMSize); // vmsize
write64(SectionDataStartOffset); // file offset
write64(SectionDataSize); // file size
} else {
write32(VMAddr); // vmaddr
write32(VMSize); // vmsize
write32(SectionDataStartOffset); // file offset
write32(SectionDataSize); // file size
}
// maxprot
write32(MaxProt);
// initprot
write32(InitProt);
write32(NumSections);
write32(0); // flags
assert(getStream().tell() - Start == SegmentLoadCommandSize);
}
void MachObjectWriter::writeSection(const MCAsmLayout &Layout,
const MCSection &Sec, uint64_t VMAddr,
uint64_t FileOffset, unsigned Flags,
uint64_t RelocationsStart,
unsigned NumRelocations) {
uint64_t SectionSize = Layout.getSectionAddressSize(&Sec);
const MCSectionMachO &Section = cast<MCSectionMachO>(Sec);
// The offset is unused for virtual sections.
if (Section.isVirtualSection()) {
assert(Layout.getSectionFileSize(&Sec) == 0 && "Invalid file size!");
FileOffset = 0;
}
// struct section (68 bytes) or
// struct section_64 (80 bytes)
uint64_t Start = getStream().tell();
(void) Start;
writeBytes(Section.getSectionName(), 16);
writeBytes(Section.getSegmentName(), 16);
if (is64Bit()) {
write64(VMAddr); // address
write64(SectionSize); // size
} else {
write32(VMAddr); // address
write32(SectionSize); // size
}
write32(FileOffset);
assert(isPowerOf2_32(Section.getAlignment()) && "Invalid alignment!");
write32(Log2_32(Section.getAlignment()));
write32(NumRelocations ? RelocationsStart : 0);
write32(NumRelocations);
write32(Flags);
write32(IndirectSymBase.lookup(&Sec)); // reserved1
write32(Section.getStubSize()); // reserved2
if (is64Bit())
write32(0); // reserved3
assert(getStream().tell() - Start ==
(is64Bit() ? sizeof(MachO::section_64) : sizeof(MachO::section)));
}
void MachObjectWriter::writeSymtabLoadCommand(uint32_t SymbolOffset,
uint32_t NumSymbols,
uint32_t StringTableOffset,
uint32_t StringTableSize) {
// struct symtab_command (24 bytes)
uint64_t Start = getStream().tell();
(void) Start;
write32(MachO::LC_SYMTAB);
write32(sizeof(MachO::symtab_command));
write32(SymbolOffset);
write32(NumSymbols);
write32(StringTableOffset);
write32(StringTableSize);
assert(getStream().tell() - Start == sizeof(MachO::symtab_command));
}
void MachObjectWriter::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 = getStream().tell();
(void) Start;
write32(MachO::LC_DYSYMTAB);
write32(sizeof(MachO::dysymtab_command));
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(getStream().tell() - Start == sizeof(MachO::dysymtab_command));
}
MachObjectWriter::MachSymbolData *
MachObjectWriter::findSymbolData(const MCSymbol &Sym) {
for (auto *SymbolData :
{&LocalSymbolData, &ExternalSymbolData, &UndefinedSymbolData})
for (MachSymbolData &Entry : *SymbolData)
if (Entry.Symbol == &Sym)
return &Entry;
return nullptr;
}
const MCSymbol &MachObjectWriter::findAliasedSymbol(const MCSymbol &Sym) const {
const MCSymbol *S = &Sym;
while (S->isVariable()) {
const MCExpr *Value = S->getVariableValue();
const auto *Ref = dyn_cast<MCSymbolRefExpr>(Value);
if (!Ref)
return *S;
S = &Ref->getSymbol();
}
return *S;
}
void MachObjectWriter::writeNlist(MachSymbolData &MSD,
const MCAsmLayout &Layout) {
const MCSymbol *Symbol = MSD.Symbol;
const MCSymbol &Data = *Symbol;
const MCSymbol *AliasedSymbol = &findAliasedSymbol(*Symbol);
uint8_t SectionIndex = MSD.SectionIndex;
uint8_t Type = 0;
uint64_t Address = 0;
bool IsAlias = Symbol != AliasedSymbol;
const MCSymbol &OrigSymbol = *Symbol;
MachSymbolData *AliaseeInfo;
if (IsAlias) {
AliaseeInfo = findSymbolData(*AliasedSymbol);
if (AliaseeInfo)
SectionIndex = AliaseeInfo->SectionIndex;
Symbol = AliasedSymbol;
// FIXME: Should this update Data as well?
}
// Set the N_TYPE bits. See <mach-o/nlist.h>.
//
// FIXME: Are the prebound or indirect fields possible here?
if (IsAlias && Symbol->isUndefined())
Type = MachO::N_INDR;
else if (Symbol->isUndefined())
Type = MachO::N_UNDF;
else if (Symbol->isAbsolute())
Type = MachO::N_ABS;
else
Type = MachO::N_SECT;
// FIXME: Set STAB bits.
if (Data.isPrivateExtern())
Type |= MachO::N_PEXT;
// Set external bit.
if (Data.isExternal() || (!IsAlias && Symbol->isUndefined()))
Type |= MachO::N_EXT;
// Compute the symbol address.
if (IsAlias && Symbol->isUndefined())
Address = AliaseeInfo->StringIndex;
else if (Symbol->isDefined())
Address = getSymbolAddress(OrigSymbol, Layout);
else if (Symbol->isCommon()) {
// Common symbols are encoded with the size in the address
// field, and their alignment in the flags.
Address = Symbol->getCommonSize();
}
// struct nlist (12 bytes)
write32(MSD.StringIndex);
write8(Type);
write8(SectionIndex);
// The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
// value.
bool EncodeAsAltEntry =
IsAlias && cast<MCSymbolMachO>(OrigSymbol).isAltEntry();
write16(cast<MCSymbolMachO>(Symbol)->getEncodedFlags(EncodeAsAltEntry));
if (is64Bit())
write64(Address);
else
write32(Address);
}
void MachObjectWriter::writeLinkeditLoadCommand(uint32_t Type,
uint32_t DataOffset,
uint32_t DataSize) {
uint64_t Start = getStream().tell();
(void) Start;
write32(Type);
write32(sizeof(MachO::linkedit_data_command));
write32(DataOffset);
write32(DataSize);
assert(getStream().tell() - Start == sizeof(MachO::linkedit_data_command));
}
static unsigned ComputeLinkerOptionsLoadCommandSize(
const std::vector<std::string> &Options, bool is64Bit)
{
unsigned Size = sizeof(MachO::linker_option_command);
for (const std::string &Option : Options)
Size += Option.size() + 1;
return alignTo(Size, is64Bit ? 8 : 4);
}
void MachObjectWriter::writeLinkerOptionsLoadCommand(
const std::vector<std::string> &Options)
{
unsigned Size = ComputeLinkerOptionsLoadCommandSize(Options, is64Bit());
uint64_t Start = getStream().tell();
(void) Start;
write32(MachO::LC_LINKER_OPTION);
write32(Size);
write32(Options.size());
uint64_t BytesWritten = sizeof(MachO::linker_option_command);
for (const std::string &Option : Options) {
// Write each string, including the null byte.
writeBytes(Option.c_str(), Option.size() + 1);
BytesWritten += Option.size() + 1;
}
// Pad to a multiple of the pointer size.
writeBytes("", OffsetToAlignment(BytesWritten, is64Bit() ? 8 : 4));
assert(getStream().tell() - Start == Size);
}
void MachObjectWriter::recordRelocation(MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
bool &IsPCRel, uint64_t &FixedValue) {
TargetObjectWriter->recordRelocation(this, Asm, Layout, Fragment, Fixup,
Target, FixedValue);
}
void MachObjectWriter::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.
// Report errors for use of .indirect_symbol not in a symbol pointer section
// or stub section.
for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
ie = Asm.indirect_symbol_end(); it != ie; ++it) {
const MCSectionMachO &Section = cast<MCSectionMachO>(*it->Section);
if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS &&
Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
Section.getType() != MachO::S_THREAD_LOCAL_VARIABLE_POINTERS &&
Section.getType() != MachO::S_SYMBOL_STUBS) {
MCSymbol &Symbol = *it->Symbol;
report_fatal_error("indirect symbol '" + Symbol.getName() +
"' not in a symbol pointer or stub section");
}
}
// Bind non-lazy symbol pointers first.
unsigned IndirectIndex = 0;
for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
const MCSectionMachO &Section = cast<MCSectionMachO>(*it->Section);
if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS &&
Section.getType() != MachO::S_THREAD_LOCAL_VARIABLE_POINTERS)
continue;
// Initialize the section indirect symbol base, if necessary.
IndirectSymBase.insert(std::make_pair(it->Section, IndirectIndex));
Asm.registerSymbol(*it->Symbol);
}
// Then lazy symbol pointers and symbol stubs.
IndirectIndex = 0;
for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
const MCSectionMachO &Section = cast<MCSectionMachO>(*it->Section);
if (Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
Section.getType() != MachO::S_SYMBOL_STUBS)
continue;
// Initialize the section indirect symbol base, if necessary.
IndirectSymBase.insert(std::make_pair(it->Section, IndirectIndex));
// Set the symbol type to undefined lazy, but only on construction.
//
// FIXME: Do not hardcode.
bool Created;
Asm.registerSymbol(*it->Symbol, &Created);
if (Created)
cast<MCSymbolMachO>(it->Symbol)->setReferenceTypeUndefinedLazy(true);
}
}
/// computeSymbolTable - Compute the symbol table data
void MachObjectWriter::computeSymbolTable(
MCAssembler &Asm, 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] = Index;
assert(Index <= 256 && "Too many sections!");
// Build the string table.
for (const MCSymbol &Symbol : Asm.symbols()) {
if (!Asm.isSymbolLinkerVisible(Symbol))
continue;
StringTable.add(Symbol.getName());
}
StringTable.finalize();
// Build the symbol arrays but only for non-local symbols.
//
// The particular order that we collect and 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 (const MCSymbol &Symbol : Asm.symbols()) {
// Ignore non-linker visible symbols.
if (!Asm.isSymbolLinkerVisible(Symbol))
continue;
if (!Symbol.isExternal() && !Symbol.isUndefined())
continue;
MachSymbolData MSD;
MSD.Symbol = &Symbol;
MSD.StringIndex = StringTable.getOffset(Symbol.getName());
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 (const MCSymbol &Symbol : Asm.symbols()) {
// Ignore non-linker visible symbols.
if (!Asm.isSymbolLinkerVisible(Symbol))
continue;
if (Symbol.isExternal() || Symbol.isUndefined())
continue;
MachSymbolData MSD;
MSD.Symbol = &Symbol;
MSD.StringIndex = StringTable.getOffset(Symbol.getName());
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 (auto *SymbolData :
{&LocalSymbolData, &ExternalSymbolData, &UndefinedSymbolData})
for (MachSymbolData &Entry : *SymbolData)
Entry.Symbol->setIndex(Index++);
for (const MCSection &Section : Asm) {
for (RelAndSymbol &Rel : Relocations[&Section]) {
if (!Rel.Sym)
continue;
// Set the Index and the IsExtern bit.
unsigned Index = Rel.Sym->getIndex();
assert(isInt<24>(Index));
if (IsLittleEndian)
Rel.MRE.r_word1 = (Rel.MRE.r_word1 & (~0U << 24)) | Index | (1 << 27);
else
Rel.MRE.r_word1 = (Rel.MRE.r_word1 & 0xff) | Index << 8 | (1 << 4);
}
}
}
void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
const MCAsmLayout &Layout) {
uint64_t StartAddress = 0;
for (const MCSection *Sec : Layout.getSectionOrder()) {
StartAddress = alignTo(StartAddress, Sec->getAlignment());
SectionAddress[Sec] = StartAddress;
StartAddress += Layout.getSectionAddressSize(Sec);
// Explicitly pad the section to match the alignment requirements of the
// following one. This is for 'gas' compatibility, it shouldn't
/// strictly be necessary.
StartAddress += getPaddingSize(Sec, Layout);
}
}
void MachObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) {
computeSectionAddresses(Asm, Layout);
// Create symbol data for any indirect symbols.
bindIndirectSymbols(Asm);
}
bool MachObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
const MCAssembler &Asm, const MCSymbol &A, const MCSymbol &B,
bool InSet) const {
// FIXME: We don't handle things like
// foo = .
// creating atoms.
if (A.isVariable() || B.isVariable())
return false;
return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, A, B,
InSet);
}
bool MachObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
bool InSet, bool IsPCRel) const {
if (InSet)
return true;
// The effective address is
// addr(atom(A)) + offset(A)
// - addr(atom(B)) - offset(B)
// and the offsets are not relocatable, so the fixup is fully resolved when
// addr(atom(A)) - addr(atom(B)) == 0.
const MCSymbol &SA = findAliasedSymbol(SymA);
const MCSection &SecA = SA.getSection();
const MCSection &SecB = *FB.getParent();
if (IsPCRel) {
// The simple (Darwin, except on x86_64) way of dealing with this was to
// assume that any reference to a temporary symbol *must* be a temporary
// symbol in the same atom, unless the sections differ. Therefore, any PCrel
// relocation to a temporary symbol (in the same section) is fully
// resolved. This also works in conjunction with absolutized .set, which
// requires the compiler to use .set to absolutize the differences between
// symbols which the compiler knows to be assembly time constants, so we
// don't need to worry about considering symbol differences fully resolved.
//
// If the file isn't using sub-sections-via-symbols, we can make the
// same assumptions about any symbol that we normally make about
// assembler locals.
bool hasReliableSymbolDifference = isX86_64();
if (!hasReliableSymbolDifference) {
if (!SA.isInSection() || &SecA != &SecB ||
(!SA.isTemporary() && FB.getAtom() != SA.getFragment()->getAtom() &&
Asm.getSubsectionsViaSymbols()))
return false;
return true;
}
// For Darwin x86_64, there is one special case when the reference IsPCRel.
// If the fragment with the reference does not have a base symbol but meets
// the simple way of dealing with this, in that it is a temporary symbol in
// the same atom then it is assumed to be fully resolved. This is needed so
// a relocation entry is not created and so the static linker does not
// mess up the reference later.
else if(!FB.getAtom() &&
SA.isTemporary() && SA.isInSection() && &SecA == &SecB){
return true;
}
}
// If they are not in the same section, we can't compute the diff.
if (&SecA != &SecB)
return false;
const MCFragment *FA = SA.getFragment();
// Bail if the symbol has no fragment.
if (!FA)
return false;
// If the atoms are the same, they are guaranteed to have the same address.
if (FA->getAtom() == FB.getAtom())
return true;
// Otherwise, we can't prove this is fully resolved.
return false;
}
void MachObjectWriter::writeObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
// Compute symbol table information and bind symbol indices.
computeSymbolTable(Asm, LocalSymbolData, ExternalSymbolData,
UndefinedSymbolData);
unsigned NumSections = Asm.size();
const MCAssembler::VersionMinInfoType &VersionInfo =
Layout.getAssembler().getVersionMinInfo();
// 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() ?
sizeof(MachO::segment_command_64) + NumSections * sizeof(MachO::section_64):
sizeof(MachO::segment_command) + NumSections * sizeof(MachO::section);
// Add the deployment target version info load command size, if used.
if (VersionInfo.Major != 0) {
++NumLoadCommands;
LoadCommandsSize += sizeof(MachO::version_min_command);
}
// Add the data-in-code load command size, if used.
unsigned NumDataRegions = Asm.getDataRegions().size();
if (NumDataRegions) {
++NumLoadCommands;
LoadCommandsSize += sizeof(MachO::linkedit_data_command);
}
// Add the loh load command size, if used.
uint64_t LOHRawSize = Asm.getLOHContainer().getEmitSize(*this, Layout);
uint64_t LOHSize = alignTo(LOHRawSize, is64Bit() ? 8 : 4);
if (LOHSize) {
++NumLoadCommands;
LoadCommandsSize += sizeof(MachO::linkedit_data_command);
}
// Add the symbol table load command sizes, if used.
unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
UndefinedSymbolData.size();
if (NumSymbols) {
NumLoadCommands += 2;
LoadCommandsSize += (sizeof(MachO::symtab_command) +
sizeof(MachO::dysymtab_command));
}
// Add the linker option load commands sizes.
for (const auto &Option : Asm.getLinkerOptions()) {
++NumLoadCommands;
LoadCommandsSize += ComputeLinkerOptionsLoadCommandSize(Option, is64Bit());
}
// Compute the total size of the section data, as well as its file size and vm
// size.
uint64_t SectionDataStart = (is64Bit() ? sizeof(MachO::mach_header_64) :
sizeof(MachO::mach_header)) + LoadCommandsSize;
uint64_t SectionDataSize = 0;
uint64_t SectionDataFileSize = 0;
uint64_t VMSize = 0;
for (const MCSection &Sec : Asm) {
uint64_t Address = getSectionAddress(&Sec);
uint64_t Size = Layout.getSectionAddressSize(&Sec);
uint64_t FileSize = Layout.getSectionFileSize(&Sec);
FileSize += getPaddingSize(&Sec, Layout);
VMSize = std::max(VMSize, Address + Size);
if (Sec.isVirtualSection())
continue;
SectionDataSize = std::max(SectionDataSize, Address + Size);
SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
}
// The section data is padded to 4 bytes.
//
// FIXME: Is this machine dependent?
unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
SectionDataFileSize += SectionDataPadding;
// Write the prolog, starting with the header and load command...
writeHeader(MachO::MH_OBJECT, NumLoadCommands, LoadCommandsSize,
Asm.getSubsectionsViaSymbols());
uint32_t Prot =
MachO::VM_PROT_READ | MachO::VM_PROT_WRITE | MachO::VM_PROT_EXECUTE;
writeSegmentLoadCommand("", NumSections, 0, VMSize, SectionDataStart,
SectionDataSize, Prot, Prot);
// ... and then the section headers.
uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
for (const MCSection &Section : Asm) {
const auto &Sec = cast<MCSectionMachO>(Section);
std::vector<RelAndSymbol> &Relocs = Relocations[&Sec];
unsigned NumRelocs = Relocs.size();
uint64_t SectionStart = SectionDataStart + getSectionAddress(&Sec);
unsigned Flags = Sec.getTypeAndAttributes();
if (Sec.hasInstructions())
Flags |= MachO::S_ATTR_SOME_INSTRUCTIONS;
writeSection(Layout, Sec, getSectionAddress(&Sec), SectionStart, Flags,
RelocTableEnd, NumRelocs);
RelocTableEnd += NumRelocs * sizeof(MachO::any_relocation_info);
}
// Write out the deployment target information, if it's available.
if (VersionInfo.Major != 0) {
assert(VersionInfo.Update < 256 && "unencodable update target version");
assert(VersionInfo.Minor < 256 && "unencodable minor target version");
assert(VersionInfo.Major < 65536 && "unencodable major target version");
uint32_t EncodedVersion = VersionInfo.Update | (VersionInfo.Minor << 8) |
(VersionInfo.Major << 16);
MachO::LoadCommandType LCType;
switch (VersionInfo.Kind) {
case MCVM_OSXVersionMin:
LCType = MachO::LC_VERSION_MIN_MACOSX;
break;
case MCVM_IOSVersionMin:
LCType = MachO::LC_VERSION_MIN_IPHONEOS;
break;
case MCVM_TvOSVersionMin:
LCType = MachO::LC_VERSION_MIN_TVOS;
break;
case MCVM_WatchOSVersionMin:
LCType = MachO::LC_VERSION_MIN_WATCHOS;
break;
}
write32(LCType);
write32(sizeof(MachO::version_min_command));
write32(EncodedVersion);
write32(0); // reserved.
}
// Write the data-in-code load command, if used.
uint64_t DataInCodeTableEnd = RelocTableEnd + NumDataRegions * 8;
if (NumDataRegions) {
uint64_t DataRegionsOffset = RelocTableEnd;
uint64_t DataRegionsSize = NumDataRegions * 8;
writeLinkeditLoadCommand(MachO::LC_DATA_IN_CODE, DataRegionsOffset,
DataRegionsSize);
}
// Write the loh load command, if used.
uint64_t LOHTableEnd = DataInCodeTableEnd + LOHSize;
if (LOHSize)
writeLinkeditLoadCommand(MachO::LC_LINKER_OPTIMIZATION_HINT,
DataInCodeTableEnd, LOHSize);
// 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 = LOHTableEnd;
// The symbol table is written after the indirect symbol data.
uint64_t SymbolTableOffset = LOHTableEnd + IndirectSymbolSize;
// The string table is written after symbol table.
uint64_t StringTableOffset =
SymbolTableOffset + NumSymTabSymbols * (is64Bit() ?
sizeof(MachO::nlist_64) :
sizeof(MachO::nlist));
writeSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
StringTableOffset, StringTable.getSize());
writeDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
FirstExternalSymbol, NumExternalSymbols,
FirstUndefinedSymbol, NumUndefinedSymbols,
IndirectSymbolOffset, NumIndirectSymbols);
}
// Write the linker options load commands.
for (const auto &Option : Asm.getLinkerOptions())
writeLinkerOptionsLoadCommand(Option);
// Write the actual section data.
for (const MCSection &Sec : Asm) {
Asm.writeSectionData(&Sec, Layout);
uint64_t Pad = getPaddingSize(&Sec, Layout);
WriteZeros(Pad);
}
// Write the extra padding.
WriteZeros(SectionDataPadding);
// Write the relocation entries.
for (const MCSection &Sec : Asm) {
// Write the section relocation entries, in reverse order to match 'as'
// (approximately, the exact algorithm is more complicated than this).
std::vector<RelAndSymbol> &Relocs = Relocations[&Sec];
for (const RelAndSymbol &Rel : make_range(Relocs.rbegin(), Relocs.rend())) {
write32(Rel.MRE.r_word0);
write32(Rel.MRE.r_word1);
}
}
// Write out the data-in-code region payload, if there is one.
for (MCAssembler::const_data_region_iterator
it = Asm.data_region_begin(), ie = Asm.data_region_end();
it != ie; ++it) {
const DataRegionData *Data = &(*it);
uint64_t Start = getSymbolAddress(*Data->Start, Layout);
uint64_t End = getSymbolAddress(*Data->End, Layout);
DEBUG(dbgs() << "data in code region-- kind: " << Data->Kind
<< " start: " << Start << "(" << Data->Start->getName() << ")"
<< " end: " << End << "(" << Data->End->getName() << ")"
<< " size: " << End - Start
<< "\n");
write32(Start);
write16(End - Start);
write16(Data->Kind);
}
// Write out the loh commands, if there is one.
if (LOHSize) {
#ifndef NDEBUG
unsigned Start = getStream().tell();
#endif
Asm.getLOHContainer().emit(*this, Layout);
// Pad to a multiple of the pointer size.
writeBytes("", OffsetToAlignment(LOHRawSize, is64Bit() ? 8 : 4));
assert(getStream().tell() - Start == LOHSize);
}
// 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->Section);
if (Section.getType() == MachO::S_NON_LAZY_SYMBOL_POINTERS) {
// If this symbol is defined and internal, mark it as such.
if (it->Symbol->isDefined() && !it->Symbol->isExternal()) {
uint32_t Flags = MachO::INDIRECT_SYMBOL_LOCAL;
if (it->Symbol->isAbsolute())
Flags |= MachO::INDIRECT_SYMBOL_ABS;
write32(Flags);
continue;
}
}
write32(it->Symbol->getIndex());
}
// FIXME: Check that offsets match computed ones.
// Write the symbol table entries.
for (auto *SymbolData :
{&LocalSymbolData, &ExternalSymbolData, &UndefinedSymbolData})
for (MachSymbolData &Entry : *SymbolData)
writeNlist(Entry, Layout);
// Write the string table.
StringTable.write(getStream());
}
}
MCObjectWriter *llvm::createMachObjectWriter(MCMachObjectTargetWriter *MOTW,
raw_pwrite_stream &OS,
bool IsLittleEndian) {
return new MachObjectWriter(MOTW, OS, IsLittleEndian);
}
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