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llvm/lib/MC/WinCOFFObjectWriter.cpp
Rui Ueyama a24db2314e MC/COFF: Do not emit forward associative section referenceds. 
MSVC link.exe cannot handle associative sections that refer later
sections in the section header. Technically, such COFF object doesn't
violate the Microsoft COFF spec, as the spec doesn't say anything
about that, but still we should avoid doing that to make it compatible
with MS tools.

This patch assigns smaller section numbers to non-associative sections
and larger numbers to associative sections. This should resolve the
compatibility issue.

Differential Revision: https://reviews.llvm.org/D30080

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295464 91177308-0d34-0410-b5e6-96231b3b80d8
2017-02-17 17:32:54 +00:00

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//===- llvm/MC/WinCOFFObjectWriter.cpp ------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains an implementation of a Win32 COFF object file writer.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCFragment.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSectionCOFF.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCSymbolCOFF.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/MCWinCOFFObjectWriter.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/COFF.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/JamCRC.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <ctime>
#include <memory>
#include <string>
#include <vector>
using namespace llvm;
using llvm::support::endian::write32le;
#define DEBUG_TYPE "WinCOFFObjectWriter"
namespace {
typedef SmallString<COFF::NameSize> name;
enum AuxiliaryType {
ATFunctionDefinition,
ATbfAndefSymbol,
ATWeakExternal,
ATFile,
ATSectionDefinition
};
struct AuxSymbol {
AuxiliaryType AuxType;
COFF::Auxiliary Aux;
};
class COFFSection;
class COFFSymbol {
public:
COFF::symbol Data = {};
typedef SmallVector<AuxSymbol, 1> AuxiliarySymbols;
name Name;
int Index;
AuxiliarySymbols Aux;
COFFSymbol *Other = nullptr;
COFFSection *Section = nullptr;
int Relocations = 0;
const MCSymbol *MC = nullptr;
COFFSymbol(StringRef Name) : Name(Name) {}
void set_name_offset(uint32_t Offset);
int64_t getIndex() const { return Index; }
void setIndex(int Value) {
Index = Value;
if (MC)
MC->setIndex(static_cast<uint32_t>(Value));
}
};
// This class contains staging data for a COFF relocation entry.
struct COFFRelocation {
COFF::relocation Data;
COFFSymbol *Symb = nullptr;
COFFRelocation() = default;
static size_t size() { return COFF::RelocationSize; }
};
typedef std::vector<COFFRelocation> relocations;
class COFFSection {
public:
COFF::section Header = {};
std::string Name;
int Number;
MCSectionCOFF const *MCSection = nullptr;
COFFSymbol *Symbol = nullptr;
relocations Relocations;
COFFSection(StringRef Name) : Name(Name) {}
};
class WinCOFFObjectWriter : public MCObjectWriter {
public:
typedef std::vector<std::unique_ptr<COFFSymbol>> symbols;
typedef std::vector<std::unique_ptr<COFFSection>> sections;
typedef DenseMap<MCSymbol const *, COFFSymbol *> symbol_map;
typedef DenseMap<MCSection const *, COFFSection *> section_map;
std::unique_ptr<MCWinCOFFObjectTargetWriter> TargetObjectWriter;
// Root level file contents.
COFF::header Header = {};
sections Sections;
symbols Symbols;
StringTableBuilder Strings{StringTableBuilder::WinCOFF};
// Maps used during object file creation.
section_map SectionMap;
symbol_map SymbolMap;
bool UseBigObj;
WinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW, raw_pwrite_stream &OS);
void reset() override {
memset(&Header, 0, sizeof(Header));
Header.Machine = TargetObjectWriter->getMachine();
Sections.clear();
Symbols.clear();
Strings.clear();
SectionMap.clear();
SymbolMap.clear();
MCObjectWriter::reset();
}
COFFSymbol *createSymbol(StringRef Name);
COFFSymbol *GetOrCreateCOFFSymbol(const MCSymbol *Symbol);
COFFSection *createSection(StringRef Name);
void defineSection(MCSectionCOFF const &Sec);
COFFSymbol *getLinkedSymbol(const MCSymbol &Symbol);
void DefineSymbol(const MCSymbol &Symbol, MCAssembler &Assembler,
const MCAsmLayout &Layout);
void SetSymbolName(COFFSymbol &S);
void SetSectionName(COFFSection &S);
bool IsPhysicalSection(COFFSection *S);
// Entity writing methods.
void WriteFileHeader(const COFF::header &Header);
void WriteSymbol(const COFFSymbol &S);
void WriteAuxiliarySymbols(const COFFSymbol::AuxiliarySymbols &S);
void writeSectionHeaders();
void WriteRelocation(const COFF::relocation &R);
uint32_t writeSectionContents(MCAssembler &Asm, const MCAsmLayout &Layout,
const MCSection &MCSec);
void writeSection(MCAssembler &Asm, const MCAsmLayout &Layout,
const COFFSection &Sec, const MCSection &MCSec);
// MCObjectWriter interface implementation.
void executePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) override;
bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
const MCSymbol &SymA,
const MCFragment &FB, bool InSet,
bool IsPCRel) const override;
bool isWeak(const MCSymbol &Sym) const override;
void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, bool &IsPCRel,
uint64_t &FixedValue) override;
void createFileSymbols(MCAssembler &Asm);
void assignSectionNumbers();
void assignFileOffsets(MCAssembler &Asm, const MCAsmLayout &Layout);
void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
};
} // end anonymous namespace
//------------------------------------------------------------------------------
// Symbol class implementation
// In the case that the name does not fit within 8 bytes, the offset
// into the string table is stored in the last 4 bytes instead, leaving
// the first 4 bytes as 0.
void COFFSymbol::set_name_offset(uint32_t Offset) {
write32le(Data.Name + 0, 0);
write32le(Data.Name + 4, Offset);
}
//------------------------------------------------------------------------------
// WinCOFFObjectWriter class implementation
WinCOFFObjectWriter::WinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW,
raw_pwrite_stream &OS)
: MCObjectWriter(OS, true), TargetObjectWriter(MOTW) {
Header.Machine = TargetObjectWriter->getMachine();
}
COFFSymbol *WinCOFFObjectWriter::createSymbol(StringRef Name) {
Symbols.push_back(make_unique<COFFSymbol>(Name));
return Symbols.back().get();
}
COFFSymbol *WinCOFFObjectWriter::GetOrCreateCOFFSymbol(const MCSymbol *Symbol) {
COFFSymbol *&Ret = SymbolMap[Symbol];
if (!Ret)
Ret = createSymbol(Symbol->getName());
return Ret;
}
COFFSection *WinCOFFObjectWriter::createSection(StringRef Name) {
Sections.emplace_back(make_unique<COFFSection>(Name));
return Sections.back().get();
}
static uint32_t getAlignment(const MCSectionCOFF &Sec) {
switch (Sec.getAlignment()) {
case 1:
return COFF::IMAGE_SCN_ALIGN_1BYTES;
case 2:
return COFF::IMAGE_SCN_ALIGN_2BYTES;
case 4:
return COFF::IMAGE_SCN_ALIGN_4BYTES;
case 8:
return COFF::IMAGE_SCN_ALIGN_8BYTES;
case 16:
return COFF::IMAGE_SCN_ALIGN_16BYTES;
case 32:
return COFF::IMAGE_SCN_ALIGN_32BYTES;
case 64:
return COFF::IMAGE_SCN_ALIGN_64BYTES;
case 128:
return COFF::IMAGE_SCN_ALIGN_128BYTES;
case 256:
return COFF::IMAGE_SCN_ALIGN_256BYTES;
case 512:
return COFF::IMAGE_SCN_ALIGN_512BYTES;
case 1024:
return COFF::IMAGE_SCN_ALIGN_1024BYTES;
case 2048:
return COFF::IMAGE_SCN_ALIGN_2048BYTES;
case 4096:
return COFF::IMAGE_SCN_ALIGN_4096BYTES;
case 8192:
return COFF::IMAGE_SCN_ALIGN_8192BYTES;
}
llvm_unreachable("unsupported section alignment");
}
/// This function takes a section data object from the assembler
/// and creates the associated COFF section staging object.
void WinCOFFObjectWriter::defineSection(const MCSectionCOFF &MCSec) {
COFFSection *Section = createSection(MCSec.getSectionName());
COFFSymbol *Symbol = createSymbol(MCSec.getSectionName());
Section->Symbol = Symbol;
Symbol->Section = Section;
Symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_STATIC;
// Create a COMDAT symbol if needed.
if (MCSec.getSelection() != COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE) {
if (const MCSymbol *S = MCSec.getCOMDATSymbol()) {
COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(S);
if (COMDATSymbol->Section)
report_fatal_error("two sections have the same comdat");
COMDATSymbol->Section = Section;
}
}
// In this case the auxiliary symbol is a Section Definition.
Symbol->Aux.resize(1);
Symbol->Aux[0] = {};
Symbol->Aux[0].AuxType = ATSectionDefinition;
Symbol->Aux[0].Aux.SectionDefinition.Selection = MCSec.getSelection();
// Set section alignment.
Section->Header.Characteristics = MCSec.getCharacteristics();
Section->Header.Characteristics |= getAlignment(MCSec);
// Bind internal COFF section to MC section.
Section->MCSection = &MCSec;
SectionMap[&MCSec] = Section;
}
static uint64_t getSymbolValue(const MCSymbol &Symbol,
const MCAsmLayout &Layout) {
if (Symbol.isCommon() && Symbol.isExternal())
return Symbol.getCommonSize();
uint64_t Res;
if (!Layout.getSymbolOffset(Symbol, Res))
return 0;
return Res;
}
COFFSymbol *WinCOFFObjectWriter::getLinkedSymbol(const MCSymbol &Symbol) {
if (!Symbol.isVariable())
return nullptr;
const MCSymbolRefExpr *SymRef =
dyn_cast<MCSymbolRefExpr>(Symbol.getVariableValue());
if (!SymRef)
return nullptr;
const MCSymbol &Aliasee = SymRef->getSymbol();
if (!Aliasee.isUndefined())
return nullptr;
return GetOrCreateCOFFSymbol(&Aliasee);
}
/// This function takes a symbol data object from the assembler
/// and creates the associated COFF symbol staging object.
void WinCOFFObjectWriter::DefineSymbol(const MCSymbol &MCSym,
MCAssembler &Assembler,
const MCAsmLayout &Layout) {
COFFSymbol *Sym = GetOrCreateCOFFSymbol(&MCSym);
const MCSymbol *Base = Layout.getBaseSymbol(MCSym);
COFFSection *Sec = nullptr;
if (Base && Base->getFragment()) {
Sec = SectionMap[Base->getFragment()->getParent()];
if (Sym->Section && Sym->Section != Sec)
report_fatal_error("conflicting sections for symbol");
}
COFFSymbol *Local = nullptr;
if (cast<MCSymbolCOFF>(MCSym).isWeakExternal()) {
Sym->Data.StorageClass = COFF::IMAGE_SYM_CLASS_WEAK_EXTERNAL;
COFFSymbol *WeakDefault = getLinkedSymbol(MCSym);
if (!WeakDefault) {
std::string WeakName = (".weak." + MCSym.getName() + ".default").str();
WeakDefault = createSymbol(WeakName);
if (!Sec)
WeakDefault->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
else
WeakDefault->Section = Sec;
Local = WeakDefault;
}
Sym->Other = WeakDefault;
// Setup the Weak External auxiliary symbol.
Sym->Aux.resize(1);
memset(&Sym->Aux[0], 0, sizeof(Sym->Aux[0]));
Sym->Aux[0].AuxType = ATWeakExternal;
Sym->Aux[0].Aux.WeakExternal.TagIndex = 0;
Sym->Aux[0].Aux.WeakExternal.Characteristics =
COFF::IMAGE_WEAK_EXTERN_SEARCH_LIBRARY;
} else {
if (!Base)
Sym->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
else
Sym->Section = Sec;
Local = Sym;
}
if (Local) {
Local->Data.Value = getSymbolValue(MCSym, Layout);
const MCSymbolCOFF &SymbolCOFF = cast<MCSymbolCOFF>(MCSym);
Local->Data.Type = SymbolCOFF.getType();
Local->Data.StorageClass = SymbolCOFF.getClass();
// If no storage class was specified in the streamer, define it here.
if (Local->Data.StorageClass == COFF::IMAGE_SYM_CLASS_NULL) {
bool IsExternal = MCSym.isExternal() ||
(!MCSym.getFragment() && !MCSym.isVariable());
Local->Data.StorageClass = IsExternal ? COFF::IMAGE_SYM_CLASS_EXTERNAL
: COFF::IMAGE_SYM_CLASS_STATIC;
}
}
Sym->MC = &MCSym;
}
// Maximum offsets for different string table entry encodings.
enum : unsigned { Max7DecimalOffset = 9999999U };
enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
// Encode a string table entry offset in base 64, padded to 6 chars, and
// prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
// Buffer must be at least 8 bytes large. No terminating null appended.
static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
"Illegal section name encoding for value");
static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/";
Buffer[0] = '/';
Buffer[1] = '/';
char *Ptr = Buffer + 7;
for (unsigned i = 0; i < 6; ++i) {
unsigned Rem = Value % 64;
Value /= 64;
*(Ptr--) = Alphabet[Rem];
}
}
void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
if (S.Name.size() <= COFF::NameSize) {
std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
return;
}
uint64_t StringTableEntry = Strings.getOffset(S.Name);
if (StringTableEntry <= Max7DecimalOffset) {
SmallVector<char, COFF::NameSize> Buffer;
Twine('/').concat(Twine(StringTableEntry)).toVector(Buffer);
assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
std::memcpy(S.Header.Name, Buffer.data(), Buffer.size());
return;
}
if (StringTableEntry <= MaxBase64Offset) {
// Starting with 10,000,000, offsets are encoded as base64.
encodeBase64StringEntry(S.Header.Name, StringTableEntry);
return;
}
report_fatal_error("COFF string table is greater than 64 GB.");
}
void WinCOFFObjectWriter::SetSymbolName(COFFSymbol &S) {
if (S.Name.size() > COFF::NameSize)
S.set_name_offset(Strings.getOffset(S.Name));
else
std::memcpy(S.Data.Name, S.Name.c_str(), S.Name.size());
}
bool WinCOFFObjectWriter::IsPhysicalSection(COFFSection *S) {
return (S->Header.Characteristics & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) ==
0;
}
//------------------------------------------------------------------------------
// entity writing methods
void WinCOFFObjectWriter::WriteFileHeader(const COFF::header &Header) {
if (UseBigObj) {
writeLE16(COFF::IMAGE_FILE_MACHINE_UNKNOWN);
writeLE16(0xFFFF);
writeLE16(COFF::BigObjHeader::MinBigObjectVersion);
writeLE16(Header.Machine);
writeLE32(Header.TimeDateStamp);
writeBytes(StringRef(COFF::BigObjMagic, sizeof(COFF::BigObjMagic)));
writeLE32(0);
writeLE32(0);
writeLE32(0);
writeLE32(0);
writeLE32(Header.NumberOfSections);
writeLE32(Header.PointerToSymbolTable);
writeLE32(Header.NumberOfSymbols);
} else {
writeLE16(Header.Machine);
writeLE16(static_cast<int16_t>(Header.NumberOfSections));
writeLE32(Header.TimeDateStamp);
writeLE32(Header.PointerToSymbolTable);
writeLE32(Header.NumberOfSymbols);
writeLE16(Header.SizeOfOptionalHeader);
writeLE16(Header.Characteristics);
}
}
void WinCOFFObjectWriter::WriteSymbol(const COFFSymbol &S) {
writeBytes(StringRef(S.Data.Name, COFF::NameSize));
writeLE32(S.Data.Value);
if (UseBigObj)
writeLE32(S.Data.SectionNumber);
else
writeLE16(static_cast<int16_t>(S.Data.SectionNumber));
writeLE16(S.Data.Type);
write8(S.Data.StorageClass);
write8(S.Data.NumberOfAuxSymbols);
WriteAuxiliarySymbols(S.Aux);
}
void WinCOFFObjectWriter::WriteAuxiliarySymbols(
const COFFSymbol::AuxiliarySymbols &S) {
for (const AuxSymbol &i : S) {
switch (i.AuxType) {
case ATFunctionDefinition:
writeLE32(i.Aux.FunctionDefinition.TagIndex);
writeLE32(i.Aux.FunctionDefinition.TotalSize);
writeLE32(i.Aux.FunctionDefinition.PointerToLinenumber);
writeLE32(i.Aux.FunctionDefinition.PointerToNextFunction);
WriteZeros(sizeof(i.Aux.FunctionDefinition.unused));
if (UseBigObj)
WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
break;
case ATbfAndefSymbol:
WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused1));
writeLE16(i.Aux.bfAndefSymbol.Linenumber);
WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused2));
writeLE32(i.Aux.bfAndefSymbol.PointerToNextFunction);
WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused3));
if (UseBigObj)
WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
break;
case ATWeakExternal:
writeLE32(i.Aux.WeakExternal.TagIndex);
writeLE32(i.Aux.WeakExternal.Characteristics);
WriteZeros(sizeof(i.Aux.WeakExternal.unused));
if (UseBigObj)
WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
break;
case ATFile:
writeBytes(
StringRef(reinterpret_cast<const char *>(&i.Aux),
UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size));
break;
case ATSectionDefinition:
writeLE32(i.Aux.SectionDefinition.Length);
writeLE16(i.Aux.SectionDefinition.NumberOfRelocations);
writeLE16(i.Aux.SectionDefinition.NumberOfLinenumbers);
writeLE32(i.Aux.SectionDefinition.CheckSum);
writeLE16(static_cast<int16_t>(i.Aux.SectionDefinition.Number));
write8(i.Aux.SectionDefinition.Selection);
WriteZeros(sizeof(i.Aux.SectionDefinition.unused));
writeLE16(static_cast<int16_t>(i.Aux.SectionDefinition.Number >> 16));
if (UseBigObj)
WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
break;
}
}
}
// Write the section header.
void WinCOFFObjectWriter::writeSectionHeaders() {
// Section numbers must be monotonically increasing in the section
// header, but our Sections array is not sorted by section number,
// so make a copy of Sections and sort it.
std::vector<COFFSection *> Arr;
for (auto &Section : Sections)
Arr.push_back(Section.get());
std::sort(Arr.begin(), Arr.end(),
[](const COFFSection *A, const COFFSection *B) {
return A->Number < B->Number;
});
for (auto &Section : Arr) {
if (Section->Number == -1)
continue;
COFF::section &S = Section->Header;
if (Section->Relocations.size() >= 0xffff)
S.Characteristics |= COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
writeBytes(StringRef(S.Name, COFF::NameSize));
writeLE32(S.VirtualSize);
writeLE32(S.VirtualAddress);
writeLE32(S.SizeOfRawData);
writeLE32(S.PointerToRawData);
writeLE32(S.PointerToRelocations);
writeLE32(S.PointerToLineNumbers);
writeLE16(S.NumberOfRelocations);
writeLE16(S.NumberOfLineNumbers);
writeLE32(S.Characteristics);
}
}
void WinCOFFObjectWriter::WriteRelocation(const COFF::relocation &R) {
writeLE32(R.VirtualAddress);
writeLE32(R.SymbolTableIndex);
writeLE16(R.Type);
}
// Write MCSec's contents. What this function does is essentially
// "Asm.writeSectionData(&MCSec, Layout)", but it's a bit complicated
// because it needs to compute a CRC.
uint32_t WinCOFFObjectWriter::writeSectionContents(MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCSection &MCSec) {
// Save the contents of the section to a temporary buffer, we need this
// to CRC the data before we dump it into the object file.
SmallVector<char, 128> Buf;
raw_svector_ostream VecOS(Buf);
raw_pwrite_stream &OldStream = getStream();
// Redirect the output stream to our buffer and fill our buffer with
// the section data.
setStream(VecOS);
Asm.writeSectionData(&MCSec, Layout);
// Reset the stream back to what it was before.
setStream(OldStream);
// Write the section contents to the object file.
getStream() << Buf;
// Calculate our CRC with an initial value of '0', this is not how
// JamCRC is specified but it aligns with the expected output.
JamCRC JC(/*Init=*/0);
JC.update(Buf);
return JC.getCRC();
}
void WinCOFFObjectWriter::writeSection(MCAssembler &Asm,
const MCAsmLayout &Layout,
const COFFSection &Sec,
const MCSection &MCSec) {
if (Sec.Number == -1)
return;
// Write the section contents.
if (Sec.Header.PointerToRawData != 0) {
assert(getStream().tell() <= Sec.Header.PointerToRawData &&
"Section::PointerToRawData is insane!");
unsigned PaddingSize = Sec.Header.PointerToRawData - getStream().tell();
assert(PaddingSize < 4 &&
"Should only need at most three bytes of padding!");
WriteZeros(PaddingSize);
uint32_t CRC = writeSectionContents(Asm, Layout, MCSec);
// Update the section definition auxiliary symbol to record the CRC.
COFFSection *Sec = SectionMap[&MCSec];
COFFSymbol::AuxiliarySymbols &AuxSyms = Sec->Symbol->Aux;
assert(AuxSyms.size() == 1 && AuxSyms[0].AuxType == ATSectionDefinition);
AuxSymbol &SecDef = AuxSyms[0];
SecDef.Aux.SectionDefinition.CheckSum = CRC;
}
// Write relocations for this section.
if (Sec.Relocations.empty()) {
assert(Sec.Header.PointerToRelocations == 0 &&
"Section::PointerToRelocations is insane!");
return;
}
assert(getStream().tell() == Sec.Header.PointerToRelocations &&
"Section::PointerToRelocations is insane!");
if (Sec.Relocations.size() >= 0xffff) {
// In case of overflow, write actual relocation count as first
// relocation. Including the synthetic reloc itself (+ 1).
COFF::relocation R;
R.VirtualAddress = Sec.Relocations.size() + 1;
R.SymbolTableIndex = 0;
R.Type = 0;
WriteRelocation(R);
}
for (const auto &Relocation : Sec.Relocations)
WriteRelocation(Relocation.Data);
}
////////////////////////////////////////////////////////////////////////////////
// MCObjectWriter interface implementations
void WinCOFFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) {
// "Define" each section & symbol. This creates section & symbol
// entries in the staging area.
for (const auto &Section : Asm)
defineSection(static_cast<const MCSectionCOFF &>(Section));
for (const MCSymbol &Symbol : Asm.symbols())
if (!Symbol.isTemporary())
DefineSymbol(Symbol, Asm, Layout);
}
bool WinCOFFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
bool InSet, bool IsPCRel) const {
// MS LINK expects to be able to replace all references to a function with a
// thunk to implement their /INCREMENTAL feature. Make sure we don't optimize
// away any relocations to functions.
uint16_t Type = cast<MCSymbolCOFF>(SymA).getType();
if (Asm.isIncrementalLinkerCompatible() &&
(Type >> COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
return false;
return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
InSet, IsPCRel);
}
bool WinCOFFObjectWriter::isWeak(const MCSymbol &Sym) const {
if (!Sym.isExternal())
return false;
if (!Sym.isInSection())
return false;
const auto &Sec = cast<MCSectionCOFF>(Sym.getSection());
if (!Sec.getCOMDATSymbol())
return false;
// It looks like for COFF it is invalid to replace a reference to a global
// in a comdat with a reference to a local.
// FIXME: Add a specification reference if available.
return true;
}
void WinCOFFObjectWriter::recordRelocation(
MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target, bool &IsPCRel, uint64_t &FixedValue) {
assert(Target.getSymA() && "Relocation must reference a symbol!");
const MCSymbol &A = Target.getSymA()->getSymbol();
if (!A.isRegistered()) {
Asm.getContext().reportError(Fixup.getLoc(),
Twine("symbol '") + A.getName() +
"' can not be undefined");
return;
}
if (A.isTemporary() && A.isUndefined()) {
Asm.getContext().reportError(Fixup.getLoc(),
Twine("assembler label '") + A.getName() +
"' can not be undefined");
return;
}
MCSection *MCSec = Fragment->getParent();
// Mark this symbol as requiring an entry in the symbol table.
assert(SectionMap.find(MCSec) != SectionMap.end() &&
"Section must already have been defined in executePostLayoutBinding!");
COFFSection *Sec = SectionMap[MCSec];
const MCSymbolRefExpr *SymB = Target.getSymB();
bool CrossSection = false;
if (SymB) {
const MCSymbol *B = &SymB->getSymbol();
if (!B->getFragment()) {
Asm.getContext().reportError(
Fixup.getLoc(),
Twine("symbol '") + B->getName() +
"' can not be undefined in a subtraction expression");
return;
}
if (!A.getFragment()) {
Asm.getContext().reportError(
Fixup.getLoc(),
Twine("symbol '") + A.getName() +
"' can not be undefined in a subtraction expression");
return;
}
CrossSection = &A.getSection() != &B->getSection();
// Offset of the symbol in the section
int64_t OffsetOfB = Layout.getSymbolOffset(*B);
// In the case where we have SymbA and SymB, we just need to store the delta
// between the two symbols. Update FixedValue to account for the delta, and
// skip recording the relocation.
if (!CrossSection) {
int64_t OffsetOfA = Layout.getSymbolOffset(A);
FixedValue = (OffsetOfA - OffsetOfB) + Target.getConstant();
return;
}
// Offset of the relocation in the section
int64_t OffsetOfRelocation =
Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
FixedValue = (OffsetOfRelocation - OffsetOfB) + Target.getConstant();
} else {
FixedValue = Target.getConstant();
}
COFFRelocation Reloc;
Reloc.Data.SymbolTableIndex = 0;
Reloc.Data.VirtualAddress = Layout.getFragmentOffset(Fragment);
// Turn relocations for temporary symbols into section relocations.
if (A.isTemporary() || CrossSection) {
MCSection *TargetSection = &A.getSection();
assert(
SectionMap.find(TargetSection) != SectionMap.end() &&
"Section must already have been defined in executePostLayoutBinding!");
Reloc.Symb = SectionMap[TargetSection]->Symbol;
FixedValue += Layout.getSymbolOffset(A);
} else {
assert(
SymbolMap.find(&A) != SymbolMap.end() &&
"Symbol must already have been defined in executePostLayoutBinding!");
Reloc.Symb = SymbolMap[&A];
}
++Reloc.Symb->Relocations;
Reloc.Data.VirtualAddress += Fixup.getOffset();
Reloc.Data.Type = TargetObjectWriter->getRelocType(
Target, Fixup, CrossSection, Asm.getBackend());
// FIXME: Can anyone explain what this does other than adjust for the size
// of the offset?
if ((Header.Machine == COFF::IMAGE_FILE_MACHINE_AMD64 &&
Reloc.Data.Type == COFF::IMAGE_REL_AMD64_REL32) ||
(Header.Machine == COFF::IMAGE_FILE_MACHINE_I386 &&
Reloc.Data.Type == COFF::IMAGE_REL_I386_REL32))
FixedValue += 4;
if (Header.Machine == COFF::IMAGE_FILE_MACHINE_ARMNT) {
switch (Reloc.Data.Type) {
case COFF::IMAGE_REL_ARM_ABSOLUTE:
case COFF::IMAGE_REL_ARM_ADDR32:
case COFF::IMAGE_REL_ARM_ADDR32NB:
case COFF::IMAGE_REL_ARM_TOKEN:
case COFF::IMAGE_REL_ARM_SECTION:
case COFF::IMAGE_REL_ARM_SECREL:
break;
case COFF::IMAGE_REL_ARM_BRANCH11:
case COFF::IMAGE_REL_ARM_BLX11:
// IMAGE_REL_ARM_BRANCH11 and IMAGE_REL_ARM_BLX11 are only used for
// pre-ARMv7, which implicitly rules it out of ARMNT (it would be valid
// for Windows CE).
case COFF::IMAGE_REL_ARM_BRANCH24:
case COFF::IMAGE_REL_ARM_BLX24:
case COFF::IMAGE_REL_ARM_MOV32A:
// IMAGE_REL_ARM_BRANCH24, IMAGE_REL_ARM_BLX24, IMAGE_REL_ARM_MOV32A are
// only used for ARM mode code, which is documented as being unsupported
// by Windows on ARM. Empirical proof indicates that masm is able to
// generate the relocations however the rest of the MSVC toolchain is
// unable to handle it.
llvm_unreachable("unsupported relocation");
break;
case COFF::IMAGE_REL_ARM_MOV32T:
break;
case COFF::IMAGE_REL_ARM_BRANCH20T:
case COFF::IMAGE_REL_ARM_BRANCH24T:
case COFF::IMAGE_REL_ARM_BLX23T:
// IMAGE_REL_BRANCH20T, IMAGE_REL_ARM_BRANCH24T, IMAGE_REL_ARM_BLX23T all
// perform a 4 byte adjustment to the relocation. Relative branches are
// offset by 4 on ARM, however, because there is no RELA relocations, all
// branches are offset by 4.
FixedValue = FixedValue + 4;
break;
}
}
// The fixed value never makes sense for section indices, ignore it.
if (Fixup.getKind() == FK_SecRel_2)
FixedValue = 0;
if (TargetObjectWriter->recordRelocation(Fixup))
Sec->Relocations.push_back(Reloc);
}
static std::time_t getTime() {
std::time_t Now = time(nullptr);
if (Now < 0 || !isUInt<32>(Now))
return UINT32_MAX;
return Now;
}
// Create .file symbols.
void WinCOFFObjectWriter::createFileSymbols(MCAssembler &Asm) {
for (const std::string &Name : Asm.getFileNames()) {
// round up to calculate the number of auxiliary symbols required
unsigned SymbolSize = UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size;
unsigned Count = (Name.size() + SymbolSize - 1) / SymbolSize;
COFFSymbol *File = createSymbol(".file");
File->Data.SectionNumber = COFF::IMAGE_SYM_DEBUG;
File->Data.StorageClass = COFF::IMAGE_SYM_CLASS_FILE;
File->Aux.resize(Count);
unsigned Offset = 0;
unsigned Length = Name.size();
for (auto &Aux : File->Aux) {
Aux.AuxType = ATFile;
if (Length > SymbolSize) {
memcpy(&Aux.Aux, Name.c_str() + Offset, SymbolSize);
Length = Length - SymbolSize;
} else {
memcpy(&Aux.Aux, Name.c_str() + Offset, Length);
memset((char *)&Aux.Aux + Length, 0, SymbolSize - Length);
break;
}
Offset += SymbolSize;
}
}
}
static bool isAssociative(const COFFSection &Section) {
return Section.Symbol->Aux[0].Aux.SectionDefinition.Selection ==
COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
}
void WinCOFFObjectWriter::assignSectionNumbers() {
size_t I = 1;
auto Assign = [&](COFFSection &Section) {
Section.Number = I;
Section.Symbol->Data.SectionNumber = I;
Section.Symbol->Aux[0].Aux.SectionDefinition.Number = I;
++I;
};
// Although it is not explicitly requested by the Microsoft COFF spec,
// we should avoid emitting forward associative section references,
// because MSVC link.exe as of 2017 cannot handle that.
for (const std::unique_ptr<COFFSection> &Section : Sections)
if (!isAssociative(*Section))
Assign(*Section);
for (const std::unique_ptr<COFFSection> &Section : Sections)
if (isAssociative(*Section))
Assign(*Section);
}
// Assign file offsets to COFF object file structures.
void WinCOFFObjectWriter::assignFileOffsets(MCAssembler &Asm,
const MCAsmLayout &Layout) {
unsigned Offset = getInitialOffset();
Offset += UseBigObj ? COFF::Header32Size : COFF::Header16Size;
Offset += COFF::SectionSize * Header.NumberOfSections;
for (const auto &Section : Asm) {
COFFSection *Sec = SectionMap[&Section];
if (Sec->Number == -1)
continue;
Sec->Header.SizeOfRawData = Layout.getSectionAddressSize(&Section);
if (IsPhysicalSection(Sec)) {
// Align the section data to a four byte boundary.
Offset = alignTo(Offset, 4);
Sec->Header.PointerToRawData = Offset;
Offset += Sec->Header.SizeOfRawData;
}
if (!Sec->Relocations.empty()) {
bool RelocationsOverflow = Sec->Relocations.size() >= 0xffff;
if (RelocationsOverflow) {
// Signal overflow by setting NumberOfRelocations to max value. Actual
// size is found in reloc #0. Microsoft tools understand this.
Sec->Header.NumberOfRelocations = 0xffff;
} else {
Sec->Header.NumberOfRelocations = Sec->Relocations.size();
}
Sec->Header.PointerToRelocations = Offset;
if (RelocationsOverflow) {
// Reloc #0 will contain actual count, so make room for it.
Offset += COFF::RelocationSize;
}
Offset += COFF::RelocationSize * Sec->Relocations.size();
for (auto &Relocation : Sec->Relocations) {
assert(Relocation.Symb->getIndex() != -1);
Relocation.Data.SymbolTableIndex = Relocation.Symb->getIndex();
}
}
assert(Sec->Symbol->Aux.size() == 1 &&
"Section's symbol must have one aux!");
AuxSymbol &Aux = Sec->Symbol->Aux[0];
assert(Aux.AuxType == ATSectionDefinition &&
"Section's symbol's aux symbol must be a Section Definition!");
Aux.Aux.SectionDefinition.Length = Sec->Header.SizeOfRawData;
Aux.Aux.SectionDefinition.NumberOfRelocations =
Sec->Header.NumberOfRelocations;
Aux.Aux.SectionDefinition.NumberOfLinenumbers =
Sec->Header.NumberOfLineNumbers;
}
Header.PointerToSymbolTable = Offset;
}
void WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
if (Sections.size() > INT32_MAX)
report_fatal_error(
"PE COFF object files can't have more than 2147483647 sections");
UseBigObj = Sections.size() > COFF::MaxNumberOfSections16;
Header.NumberOfSections = Sections.size();
Header.NumberOfSymbols = 0;
assignSectionNumbers();
createFileSymbols(Asm);
for (auto &Symbol : Symbols) {
// Update section number & offset for symbols that have them.
if (Symbol->Section)
Symbol->Data.SectionNumber = Symbol->Section->Number;
Symbol->setIndex(Header.NumberOfSymbols++);
// Update auxiliary symbol info.
Symbol->Data.NumberOfAuxSymbols = Symbol->Aux.size();
Header.NumberOfSymbols += Symbol->Data.NumberOfAuxSymbols;
}
// Build string table.
for (const auto &S : Sections)
if (S->Name.size() > COFF::NameSize)
Strings.add(S->Name);
for (const auto &S : Symbols)
if (S->Name.size() > COFF::NameSize)
Strings.add(S->Name);
Strings.finalize();
// Set names.
for (const auto &S : Sections)
SetSectionName(*S);
for (auto &S : Symbols)
SetSymbolName(*S);
// Fixup weak external references.
for (auto &Symbol : Symbols) {
if (Symbol->Other) {
assert(Symbol->getIndex() != -1);
assert(Symbol->Aux.size() == 1 && "Symbol must contain one aux symbol!");
assert(Symbol->Aux[0].AuxType == ATWeakExternal &&
"Symbol's aux symbol must be a Weak External!");
Symbol->Aux[0].Aux.WeakExternal.TagIndex = Symbol->Other->getIndex();
}
}
// Fixup associative COMDAT sections.
for (auto &Section : Sections) {
if (Section->Symbol->Aux[0].Aux.SectionDefinition.Selection !=
COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
continue;
const MCSectionCOFF &MCSec = *Section->MCSection;
const MCSymbol *COMDAT = MCSec.getCOMDATSymbol();
assert(COMDAT);
COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(COMDAT);
assert(COMDATSymbol);
COFFSection *Assoc = COMDATSymbol->Section;
if (!Assoc)
report_fatal_error(
Twine("Missing associated COMDAT section for section ") +
MCSec.getSectionName());
// Skip this section if the associated section is unused.
if (Assoc->Number == -1)
continue;
Section->Symbol->Aux[0].Aux.SectionDefinition.Number = Assoc->Number;
}
assignFileOffsets(Asm, Layout);
// MS LINK expects to be able to use this timestamp to implement their
// /INCREMENTAL feature.
if (Asm.isIncrementalLinkerCompatible()) {
Header.TimeDateStamp = getTime();
} else {
// Have deterministic output if /INCREMENTAL isn't needed. Also matches GNU.
Header.TimeDateStamp = 0;
}
// Write it all to disk...
WriteFileHeader(Header);
writeSectionHeaders();
// Write section contents.
sections::iterator I = Sections.begin();
sections::iterator IE = Sections.end();
MCAssembler::iterator J = Asm.begin();
MCAssembler::iterator JE = Asm.end();
for (; I != IE && J != JE; ++I, ++J)
writeSection(Asm, Layout, **I, *J);
assert(getStream().tell() == Header.PointerToSymbolTable &&
"Header::PointerToSymbolTable is insane!");
// Write a symbol table.
for (auto &Symbol : Symbols)
if (Symbol->getIndex() != -1)
WriteSymbol(*Symbol);
// Write a string table, which completes the entire COFF file.
Strings.write(getStream());
}
MCWinCOFFObjectTargetWriter::MCWinCOFFObjectTargetWriter(unsigned Machine_)
: Machine(Machine_) {}
// Pin the vtable to this file.
void MCWinCOFFObjectTargetWriter::anchor() {}
//------------------------------------------------------------------------------
// WinCOFFObjectWriter factory function
MCObjectWriter *
llvm::createWinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW,
raw_pwrite_stream &OS) {
return new WinCOFFObjectWriter(MOTW, OS);
}
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