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WasmObjectWriter.cpp
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//===- lib/MC/WasmObjectWriter.cpp - Wasm File Writer ---------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements Wasm object file writer information.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/BinaryFormat/Wasm.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionWasm.h"
#include "llvm/MC/MCSymbolWasm.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/MCWasmObjectWriter.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/StringSaver.h"
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "mc"
namespace {
// Went we ceate the indirect function table we start at 1, so that there is
// and emtpy slot at 0 and therefore calling a null function pointer will trap.
static const uint32_t kInitialTableOffset = 1;
// For patching purposes, we need to remember where each section starts, both
// for patching up the section size field, and for patching up references to
// locations within the section.
struct SectionBookkeeping {
// Where the size of the section is written.
uint64_t SizeOffset;
// Where the section header ends (without custom section name).
uint64_t PayloadOffset;
// Where the contents of the section starts.
uint64_t ContentsOffset;
uint32_t Index;
};
// The signature of a wasm function, in a struct capable of being used as a
// DenseMap key.
struct WasmFunctionType {
// Support empty and tombstone instances, needed by DenseMap.
enum { Plain, Empty, Tombstone } State;
// The return types of the function.
SmallVector<wasm::ValType, 1> Returns;
// The parameter types of the function.
SmallVector<wasm::ValType, 4> Params;
WasmFunctionType() : State(Plain) {}
bool operator==(const WasmFunctionType &Other) const {
return State == Other.State && Returns == Other.Returns &&
Params == Other.Params;
}
};
// Traits for using WasmFunctionType in a DenseMap.
struct WasmFunctionTypeDenseMapInfo {
static WasmFunctionType getEmptyKey() {
WasmFunctionType FuncTy;
FuncTy.State = WasmFunctionType::Empty;
return FuncTy;
}
static WasmFunctionType getTombstoneKey() {
WasmFunctionType FuncTy;
FuncTy.State = WasmFunctionType::Tombstone;
return FuncTy;
}
static unsigned getHashValue(const WasmFunctionType &FuncTy) {
uintptr_t Value = FuncTy.State;
for (wasm::ValType Ret : FuncTy.Returns)
Value += DenseMapInfo<int32_t>::getHashValue(int32_t(Ret));
for (wasm::ValType Param : FuncTy.Params)
Value += DenseMapInfo<int32_t>::getHashValue(int32_t(Param));
return Value;
}
static bool isEqual(const WasmFunctionType &LHS,
const WasmFunctionType &RHS) {
return LHS == RHS;
}
};
// A wasm data segment. A wasm binary contains only a single data section
// but that can contain many segments, each with their own virtual location
// in memory. Each MCSection data created by llvm is modeled as its own
// wasm data segment.
struct WasmDataSegment {
MCSectionWasm *Section;
StringRef Name;
uint32_t Offset;
uint32_t Alignment;
uint32_t Flags;
SmallVector<char, 4> Data;
};
// A wasm function to be written into the function section.
struct WasmFunction {
int32_t Type;
const MCSymbolWasm *Sym;
};
// A wasm global to be written into the global section.
struct WasmGlobal {
wasm::WasmGlobalType Type;
uint64_t InitialValue;
};
// Information about a single item which is part of a COMDAT. For each data
// segment or function which is in the COMDAT, there is a corresponding
// WasmComdatEntry.
struct WasmComdatEntry {
unsigned Kind;
uint32_t Index;
};
// Information about a single relocation.
struct WasmRelocationEntry {
uint64_t Offset; // Where is the relocation.
const MCSymbolWasm *Symbol; // The symbol to relocate with.
int64_t Addend; // A value to add to the symbol.
unsigned Type; // The type of the relocation.
const MCSectionWasm *FixupSection;// The section the relocation is targeting.
WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol,
int64_t Addend, unsigned Type,
const MCSectionWasm *FixupSection)
: Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type),
FixupSection(FixupSection) {}
bool hasAddend() const {
switch (Type) {
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
case wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32:
case wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32:
return true;
default:
return false;
}
}
void print(raw_ostream &Out) const {
Out << wasm::relocTypetoString(Type)
<< " Off=" << Offset << ", Sym=" << *Symbol << ", Addend=" << Addend
<< ", FixupSection=" << FixupSection->getSectionName();
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
#endif
};
static const uint32_t INVALID_INDEX = -1;
struct WasmCustomSection {
StringRef Name;
MCSectionWasm *Section;
uint32_t OutputContentsOffset;
uint32_t OutputIndex;
WasmCustomSection(StringRef Name, MCSectionWasm *Section)
: Name(Name), Section(Section), OutputContentsOffset(0),
OutputIndex(INVALID_INDEX) {}
};
#if !defined(NDEBUG)
raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) {
Rel.print(OS);
return OS;
}
#endif
class WasmObjectWriter : public MCObjectWriter {
support::endian::Writer W;
/// The target specific Wasm writer instance.
std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter;
// Relocations for fixing up references in the code section.
std::vector<WasmRelocationEntry> CodeRelocations;
uint32_t CodeSectionIndex;
// Relocations for fixing up references in the data section.
std::vector<WasmRelocationEntry> DataRelocations;
uint32_t DataSectionIndex;
// Index values to use for fixing up call_indirect type indices.
// Maps function symbols to the index of the type of the function
DenseMap<const MCSymbolWasm *, uint32_t> TypeIndices;
// Maps function symbols to the table element index space. Used
// for TABLE_INDEX relocation types (i.e. address taken functions).
DenseMap<const MCSymbolWasm *, uint32_t> TableIndices;
// Maps function/global symbols to the function/global/section index space.
DenseMap<const MCSymbolWasm *, uint32_t> WasmIndices;
// Maps data symbols to the Wasm segment and offset/size with the segment.
DenseMap<const MCSymbolWasm *, wasm::WasmDataReference> DataLocations;
// Stores output data (index, relocations, content offset) for custom
// section.
std::vector<WasmCustomSection> CustomSections;
// Relocations for fixing up references in the custom sections.
DenseMap<const MCSectionWasm *, std::vector<WasmRelocationEntry>>
CustomSectionsRelocations;
// Map from section to defining function symbol.
DenseMap<const MCSection *, const MCSymbol *> SectionFunctions;
DenseMap<WasmFunctionType, int32_t, WasmFunctionTypeDenseMapInfo>
FunctionTypeIndices;
SmallVector<WasmFunctionType, 4> FunctionTypes;
SmallVector<WasmGlobal, 4> Globals;
SmallVector<WasmDataSegment, 4> DataSegments;
unsigned NumFunctionImports = 0;
unsigned NumGlobalImports = 0;
uint32_t SectionCount = 0;
// TargetObjectWriter wrappers.
bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
unsigned getRelocType(const MCValue &Target, const MCFixup &Fixup) const {
return TargetObjectWriter->getRelocType(Target, Fixup);
}
void startSection(SectionBookkeeping &Section, unsigned SectionId);
void startCustomSection(SectionBookkeeping &Section, StringRef Name);
void endSection(SectionBookkeeping &Section);
public:
WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
raw_pwrite_stream &OS)
: W(OS, support::little), TargetObjectWriter(std::move(MOTW)) {}
~WasmObjectWriter() override;
private:
void reset() override {
CodeRelocations.clear();
DataRelocations.clear();
TypeIndices.clear();
WasmIndices.clear();
TableIndices.clear();
DataLocations.clear();
CustomSectionsRelocations.clear();
FunctionTypeIndices.clear();
FunctionTypes.clear();
Globals.clear();
DataSegments.clear();
SectionFunctions.clear();
NumFunctionImports = 0;
NumGlobalImports = 0;
MCObjectWriter::reset();
}
void writeHeader(const MCAssembler &Asm);
void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, uint64_t &FixedValue) override;
void executePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) override;
uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
void writeString(const StringRef Str) {
encodeULEB128(Str.size(), W.OS);
W.OS << Str;
}
void writeValueType(wasm::ValType Ty) {
W.OS << static_cast<char>(Ty);
}
void writeTypeSection(ArrayRef<WasmFunctionType> FunctionTypes);
void writeImportSection(ArrayRef<wasm::WasmImport> Imports, uint32_t DataSize,
uint32_t NumElements);
void writeFunctionSection(ArrayRef<WasmFunction> Functions);
void writeGlobalSection();
void writeExportSection(ArrayRef<wasm::WasmExport> Exports);
void writeElemSection(ArrayRef<uint32_t> TableElems);
void writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
ArrayRef<WasmFunction> Functions);
void writeDataSection();
void writeRelocSection(uint32_t SectionIndex, StringRef Name,
ArrayRef<WasmRelocationEntry> Relocations);
void writeLinkingMetaDataSection(
ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats);
void writeCustomSections(const MCAssembler &Asm, const MCAsmLayout &Layout);
void writeCustomRelocSections();
void
updateCustomSectionRelocations(const SmallVector<WasmFunction, 4> &Functions,
const MCAsmLayout &Layout);
uint32_t getProvisionalValue(const WasmRelocationEntry &RelEntry);
void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
uint64_t ContentsOffset);
uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry);
uint32_t getFunctionType(const MCSymbolWasm &Symbol);
uint32_t registerFunctionType(const MCSymbolWasm &Symbol);
};
} // end anonymous namespace
WasmObjectWriter::~WasmObjectWriter() {}
// Write out a section header and a patchable section size field.
void WasmObjectWriter::startSection(SectionBookkeeping &Section,
unsigned SectionId) {
LLVM_DEBUG(dbgs() << "startSection " << SectionId << "\n");
W.OS << char(SectionId);
Section.SizeOffset = W.OS.tell();
// The section size. We don't know the size yet, so reserve enough space
// for any 32-bit value; we'll patch it later.
encodeULEB128(UINT32_MAX, W.OS);
// The position where the section starts, for measuring its size.
Section.ContentsOffset = W.OS.tell();
Section.PayloadOffset = W.OS.tell();
Section.Index = SectionCount++;
}
void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section,
StringRef Name) {
LLVM_DEBUG(dbgs() << "startCustomSection " << Name << "\n");
startSection(Section, wasm::WASM_SEC_CUSTOM);
// The position where the section header ends, for measuring its size.
Section.PayloadOffset = W.OS.tell();
// Custom sections in wasm also have a string identifier.
writeString(Name);
// The position where the custom section starts.
Section.ContentsOffset = W.OS.tell();
}
// Now that the section is complete and we know how big it is, patch up the
// section size field at the start of the section.
void WasmObjectWriter::endSection(SectionBookkeeping &Section) {
uint64_t Size = W.OS.tell() - Section.PayloadOffset;
if (uint32_t(Size) != Size)
report_fatal_error("section size does not fit in a uint32_t");
LLVM_DEBUG(dbgs() << "endSection size=" << Size << "\n");
// Write the final section size to the payload_len field, which follows
// the section id byte.
uint8_t Buffer[16];
unsigned SizeLen = encodeULEB128(Size, Buffer, 5);
assert(SizeLen == 5);
static_cast<raw_pwrite_stream &>(W.OS).pwrite((char *)Buffer, SizeLen,
Section.SizeOffset);
}
// Emit the Wasm header.
void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
W.OS.write(wasm::WasmMagic, sizeof(wasm::WasmMagic));
W.write<uint32_t>(wasm::WasmVersion);
}
void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) {
// Build a map of sections to the function that defines them, for use
// in recordRelocation.
for (const MCSymbol &S : Asm.symbols()) {
const auto &WS = static_cast<const MCSymbolWasm &>(S);
if (WS.isDefined() && WS.isFunction() && !WS.isVariable()) {
const auto &Sec = static_cast<const MCSectionWasm &>(S.getSection());
auto Pair = SectionFunctions.insert(std::make_pair(&Sec, &S));
if (!Pair.second)
report_fatal_error("section already has a defining function: " +
Sec.getSectionName());
}
}
}
void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
MCAsmBackend &Backend = Asm.getBackend();
bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
MCFixupKindInfo::FKF_IsPCRel;
const auto &FixupSection = cast<MCSectionWasm>(*Fragment->getParent());
uint64_t C = Target.getConstant();
uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
MCContext &Ctx = Asm.getContext();
// The .init_array isn't translated as data, so don't do relocations in it.
if (FixupSection.getSectionName().startswith(".init_array"))
return;
if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
"Should not have constructed this");
// Let A, B and C being the components of Target and R be the location of
// the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
// If it is pcrel, we want to compute (A - B + C - R).
// In general, Wasm has no relocations for -B. It can only represent (A + C)
// or (A + C - R). If B = R + K and the relocation is not pcrel, we can
// replace B to implement it: (A - R - K + C)
if (IsPCRel) {
Ctx.reportError(
Fixup.getLoc(),
"No relocation available to represent this relative expression");
return;
}
const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol());
if (SymB.isUndefined()) {
Ctx.reportError(Fixup.getLoc(),
Twine("symbol '") + SymB.getName() +
"' can not be undefined in a subtraction expression");
return;
}
assert(!SymB.isAbsolute() && "Should have been folded");
const MCSection &SecB = SymB.getSection();
if (&SecB != &FixupSection) {
Ctx.reportError(Fixup.getLoc(),
"Cannot represent a difference across sections");
return;
}
uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
uint64_t K = SymBOffset - FixupOffset;
IsPCRel = true;
C -= K;
}
// We either rejected the fixup or folded B into C at this point.
const MCSymbolRefExpr *RefA = Target.getSymA();
const auto *SymA = RefA ? cast<MCSymbolWasm>(&RefA->getSymbol()) : nullptr;
if (SymA && SymA->isVariable()) {
const MCExpr *Expr = SymA->getVariableValue();
const auto *Inner = cast<MCSymbolRefExpr>(Expr);
if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
llvm_unreachable("weakref used in reloc not yet implemented");
}
// Put any constant offset in an addend. Offsets can be negative, and
// LLVM expects wrapping, in contrast to wasm's immediates which can't
// be negative and don't wrap.
FixedValue = 0;
unsigned Type = getRelocType(Target, Fixup);
assert(!IsPCRel);
assert(SymA);
// Absolute offset within a section or a function.
// Currently only supported for for metadata sections.
// See: test/MC/WebAssembly/blockaddress.ll
if (Type == wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32 ||
Type == wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32) {
if (!FixupSection.getKind().isMetadata())
report_fatal_error("relocations for function or section offsets are "
"only supported in metadata sections");
const MCSymbol *SectionSymbol = nullptr;
const MCSection &SecA = SymA->getSection();
if (SecA.getKind().isText())
SectionSymbol = SectionFunctions.find(&SecA)->second;
else
SectionSymbol = SecA.getBeginSymbol();
if (!SectionSymbol)
report_fatal_error("section symbol is required for relocation");
C += Layout.getSymbolOffset(*SymA);
SymA = cast<MCSymbolWasm>(SectionSymbol);
}
// Relocation other than R_WEBASSEMBLY_TYPE_INDEX_LEB are required to be
// against a named symbol.
if (Type != wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB) {
if (SymA->getName().empty())
report_fatal_error("relocations against un-named temporaries are not yet "
"supported by wasm");
SymA->setUsedInReloc();
}
WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
LLVM_DEBUG(dbgs() << "WasmReloc: " << Rec << "\n");
if (FixupSection.isWasmData()) {
DataRelocations.push_back(Rec);
} else if (FixupSection.getKind().isText()) {
CodeRelocations.push_back(Rec);
} else if (FixupSection.getKind().isMetadata()) {
CustomSectionsRelocations[&FixupSection].push_back(Rec);
} else {
llvm_unreachable("unexpected section type");
}
}
// Write X as an (unsigned) LEB value at offset Offset in Stream, padded
// to allow patching.
static void
WritePatchableLEB(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
uint8_t Buffer[5];
unsigned SizeLen = encodeULEB128(X, Buffer, 5);
assert(SizeLen == 5);
Stream.pwrite((char *)Buffer, SizeLen, Offset);
}
// Write X as an signed LEB value at offset Offset in Stream, padded
// to allow patching.
static void
WritePatchableSLEB(raw_pwrite_stream &Stream, int32_t X, uint64_t Offset) {
uint8_t Buffer[5];
unsigned SizeLen = encodeSLEB128(X, Buffer, 5);
assert(SizeLen == 5);
Stream.pwrite((char *)Buffer, SizeLen, Offset);
}
// Write X as a plain integer value at offset Offset in Stream.
static void WriteI32(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
uint8_t Buffer[4];
support::endian::write32le(Buffer, X);
Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
}
static const MCSymbolWasm* ResolveSymbol(const MCSymbolWasm& Symbol) {
if (Symbol.isVariable()) {
const MCExpr *Expr = Symbol.getVariableValue();
auto *Inner = cast<MCSymbolRefExpr>(Expr);
return cast<MCSymbolWasm>(&Inner->getSymbol());
}
return &Symbol;
}
// Compute a value to write into the code at the location covered
// by RelEntry. This value isn't used by the static linker; it just serves
// to make the object format more readable and more likely to be directly
// useable.
uint32_t
WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry) {
switch (RelEntry.Type) {
case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32: {
// Provisional value is table address of the resolved symbol itself
const MCSymbolWasm *Sym = ResolveSymbol(*RelEntry.Symbol);
assert(Sym->isFunction());
return TableIndices[Sym];
}
case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
// Provisional value is same as the index
return getRelocationIndexValue(RelEntry);
case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
// Provisional value is function/global Wasm index
if (!WasmIndices.count(RelEntry.Symbol))
report_fatal_error("symbol not found in wasm index space: " +
RelEntry.Symbol->getName());
return WasmIndices[RelEntry.Symbol];
case wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32:
case wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32: {
const auto &Section =
static_cast<const MCSectionWasm &>(RelEntry.Symbol->getSection());
return Section.getSectionOffset() + RelEntry.Addend;
}
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB: {
// Provisional value is address of the global
const MCSymbolWasm *Sym = ResolveSymbol(*RelEntry.Symbol);
// For undefined symbols, use zero
if (!Sym->isDefined())
return 0;
const wasm::WasmDataReference &Ref = DataLocations[Sym];
const WasmDataSegment &Segment = DataSegments[Ref.Segment];
// Ignore overflow. LLVM allows address arithmetic to silently wrap.
return Segment.Offset + Ref.Offset + RelEntry.Addend;
}
default:
llvm_unreachable("invalid relocation type");
}
}
static void addData(SmallVectorImpl<char> &DataBytes,
MCSectionWasm &DataSection) {
LLVM_DEBUG(errs() << "addData: " << DataSection.getSectionName() << "\n");
DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment()));
for (const MCFragment &Frag : DataSection) {
if (Frag.hasInstructions())
report_fatal_error("only data supported in data sections");
if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) {
if (Align->getValueSize() != 1)
report_fatal_error("only byte values supported for alignment");
// If nops are requested, use zeros, as this is the data section.
uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue();
uint64_t Size = std::min<uint64_t>(alignTo(DataBytes.size(),
Align->getAlignment()),
DataBytes.size() +
Align->getMaxBytesToEmit());
DataBytes.resize(Size, Value);
} else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) {
int64_t NumValues;
if (!Fill->getNumValues().evaluateAsAbsolute(NumValues))
llvm_unreachable("The fill should be an assembler constant");
DataBytes.insert(DataBytes.end(), Fill->getValueSize() * NumValues,
Fill->getValue());
} else {
const auto &DataFrag = cast<MCDataFragment>(Frag);
const SmallVectorImpl<char> &Contents = DataFrag.getContents();
DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
}
}
LLVM_DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n");
}
uint32_t
WasmObjectWriter::getRelocationIndexValue(const WasmRelocationEntry &RelEntry) {
if (RelEntry.Type == wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB) {
if (!TypeIndices.count(RelEntry.Symbol))
report_fatal_error("symbol not found in type index space: " +
RelEntry.Symbol->getName());
return TypeIndices[RelEntry.Symbol];
}
return RelEntry.Symbol->getIndex();
}
// Apply the portions of the relocation records that we can handle ourselves
// directly.
void WasmObjectWriter::applyRelocations(
ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset) {
auto &Stream = static_cast<raw_pwrite_stream &>(W.OS);
for (const WasmRelocationEntry &RelEntry : Relocations) {
uint64_t Offset = ContentsOffset +
RelEntry.FixupSection->getSectionOffset() +
RelEntry.Offset;
LLVM_DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n");
uint32_t Value = getProvisionalValue(RelEntry);
switch (RelEntry.Type) {
case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
WritePatchableLEB(Stream, Value, Offset);
break;
case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
case wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32:
case wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32:
WriteI32(Stream, Value, Offset);
break;
case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
WritePatchableSLEB(Stream, Value, Offset);
break;
default:
llvm_unreachable("invalid relocation type");
}
}
}
void WasmObjectWriter::writeTypeSection(
ArrayRef<WasmFunctionType> FunctionTypes) {
if (FunctionTypes.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_TYPE);
encodeULEB128(FunctionTypes.size(), W.OS);
for (const WasmFunctionType &FuncTy : FunctionTypes) {
W.OS << char(wasm::WASM_TYPE_FUNC);
encodeULEB128(FuncTy.Params.size(), W.OS);
for (wasm::ValType Ty : FuncTy.Params)
writeValueType(Ty);
encodeULEB128(FuncTy.Returns.size(), W.OS);
for (wasm::ValType Ty : FuncTy.Returns)
writeValueType(Ty);
}
endSection(Section);
}
void WasmObjectWriter::writeImportSection(ArrayRef<wasm::WasmImport> Imports,
uint32_t DataSize,
uint32_t NumElements) {
if (Imports.empty())
return;
uint32_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_IMPORT);
encodeULEB128(Imports.size(), W.OS);
for (const wasm::WasmImport &Import : Imports) {
writeString(Import.Module);
writeString(Import.Field);
W.OS << char(Import.Kind);
switch (Import.Kind) {
case wasm::WASM_EXTERNAL_FUNCTION:
encodeULEB128(Import.SigIndex, W.OS);
break;
case wasm::WASM_EXTERNAL_GLOBAL:
W.OS << char(Import.Global.Type);
W.OS << char(Import.Global.Mutable ? 1 : 0);
break;
case wasm::WASM_EXTERNAL_MEMORY:
encodeULEB128(0, W.OS); // flags
encodeULEB128(NumPages, W.OS); // initial
break;
case wasm::WASM_EXTERNAL_TABLE:
W.OS << char(Import.Table.ElemType);
encodeULEB128(0, W.OS); // flags
encodeULEB128(NumElements, W.OS); // initial
break;
default:
llvm_unreachable("unsupported import kind");
}
}
endSection(Section);
}
void WasmObjectWriter::writeFunctionSection(ArrayRef<WasmFunction> Functions) {
if (Functions.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_FUNCTION);
encodeULEB128(Functions.size(), W.OS);
for (const WasmFunction &Func : Functions)
encodeULEB128(Func.Type, W.OS);
endSection(Section);
}
void WasmObjectWriter::writeGlobalSection() {
if (Globals.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_GLOBAL);
encodeULEB128(Globals.size(), W.OS);
for (const WasmGlobal &Global : Globals) {
writeValueType(static_cast<wasm::ValType>(Global.Type.Type));
W.OS << char(Global.Type.Mutable);
W.OS << char(wasm::WASM_OPCODE_I32_CONST);
encodeSLEB128(Global.InitialValue, W.OS);
W.OS << char(wasm::WASM_OPCODE_END);
}
endSection(Section);
}
void WasmObjectWriter::writeExportSection(ArrayRef<wasm::WasmExport> Exports) {
if (Exports.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_EXPORT);
encodeULEB128(Exports.size(), W.OS);
for (const wasm::WasmExport &Export : Exports) {
writeString(Export.Name);
W.OS << char(Export.Kind);
encodeULEB128(Export.Index, W.OS);
}
endSection(Section);
}
void WasmObjectWriter::writeElemSection(ArrayRef<uint32_t> TableElems) {
if (TableElems.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_ELEM);
encodeULEB128(1, W.OS); // number of "segments"
encodeULEB128(0, W.OS); // the table index
// init expr for starting offset
W.OS << char(wasm::WASM_OPCODE_I32_CONST);
encodeSLEB128(kInitialTableOffset, W.OS);
W.OS << char(wasm::WASM_OPCODE_END);
encodeULEB128(TableElems.size(), W.OS);
for (uint32_t Elem : TableElems)
encodeULEB128(Elem, W.OS);
endSection(Section);
}
void WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
const MCAsmLayout &Layout,
ArrayRef<WasmFunction> Functions) {
if (Functions.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_CODE);
CodeSectionIndex = Section.Index;
encodeULEB128(Functions.size(), W.OS);
for (const WasmFunction &Func : Functions) {
auto &FuncSection = static_cast<MCSectionWasm &>(Func.Sym->getSection());
int64_t Size = 0;
if (!Func.Sym->getSize()->evaluateAsAbsolute(Size, Layout))
report_fatal_error(".size expression must be evaluatable");
encodeULEB128(Size, W.OS);
FuncSection.setSectionOffset(W.OS.tell() - Section.ContentsOffset);
Asm.writeSectionData(W.OS, &FuncSection, Layout);
}
// Apply fixups.
applyRelocations(CodeRelocations, Section.ContentsOffset);
endSection(Section);
}
void WasmObjectWriter::writeDataSection() {
if (DataSegments.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_DATA);
DataSectionIndex = Section.Index;
encodeULEB128(DataSegments.size(), W.OS); // count
for (const WasmDataSegment &Segment : DataSegments) {
encodeULEB128(0, W.OS); // memory index
W.OS << char(wasm::WASM_OPCODE_I32_CONST);
encodeSLEB128(Segment.Offset, W.OS); // offset
W.OS << char(wasm::WASM_OPCODE_END);
encodeULEB128(Segment.Data.size(), W.OS); // size
Segment.Section->setSectionOffset(W.OS.tell() - Section.ContentsOffset);
W.OS << Segment.Data; // data
}
// Apply fixups.
applyRelocations(DataRelocations, Section.ContentsOffset);
endSection(Section);
}
void WasmObjectWriter::writeRelocSection(
uint32_t SectionIndex, StringRef Name,
ArrayRef<WasmRelocationEntry> Relocations) {
// See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
// for descriptions of the reloc sections.
if (Relocations.empty())
return;
SectionBookkeeping Section;
startCustomSection(Section, std::string("reloc.") + Name.str());
encodeULEB128(SectionIndex, W.OS);
encodeULEB128(Relocations.size(), W.OS);
for (const WasmRelocationEntry& RelEntry : Relocations) {
uint64_t Offset = RelEntry.Offset +
RelEntry.FixupSection->getSectionOffset();
uint32_t Index = getRelocationIndexValue(RelEntry);
W.OS << char(RelEntry.Type);
encodeULEB128(Offset, W.OS);
encodeULEB128(Index, W.OS);
if (RelEntry.hasAddend())
encodeSLEB128(RelEntry.Addend, W.OS);
}
endSection(Section);
}
void WasmObjectWriter::writeCustomRelocSections() {
for (const auto &Sec : CustomSections) {
auto &Relocations = CustomSectionsRelocations[Sec.Section];
writeRelocSection(Sec.OutputIndex, Sec.Name, Relocations);
}
}
void WasmObjectWriter::writeLinkingMetaDataSection(
ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats) {
SectionBookkeeping Section;
startCustomSection(Section, "linking");
encodeULEB128(wasm::WasmMetadataVersion, W.OS);
SectionBookkeeping SubSection;
if (SymbolInfos.size() != 0) {
startSection(SubSection, wasm::WASM_SYMBOL_TABLE);
encodeULEB128(SymbolInfos.size(), W.OS);
for (const wasm::WasmSymbolInfo &Sym : SymbolInfos) {
encodeULEB128(Sym.Kind, W.OS);
encodeULEB128(Sym.Flags, W.OS);
switch (Sym.Kind) {
case wasm::WASM_SYMBOL_TYPE_FUNCTION:
case wasm::WASM_SYMBOL_TYPE_GLOBAL:
encodeULEB128(Sym.ElementIndex, W.OS);
if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0)
writeString(Sym.Name);
break;
case wasm::WASM_SYMBOL_TYPE_DATA:
writeString(Sym.Name);
if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0) {
encodeULEB128(Sym.DataRef.Segment, W.OS);
encodeULEB128(Sym.DataRef.Offset, W.OS);
encodeULEB128(Sym.DataRef.Size, W.OS);
}
break;
case wasm::WASM_SYMBOL_TYPE_SECTION: {
const uint32_t SectionIndex =
CustomSections[Sym.ElementIndex].OutputIndex;
encodeULEB128(SectionIndex, W.OS);
break;
}
default:
llvm_unreachable("unexpected kind");
}
}
endSection(SubSection);
}
if (DataSegments.size()) {
startSection(SubSection, wasm::WASM_SEGMENT_INFO);
encodeULEB128(DataSegments.size(), W.OS);
for (const WasmDataSegment &Segment : DataSegments) {
writeString(Segment.Name);
encodeULEB128(Segment.Alignment, W.OS);
encodeULEB128(Segment.Flags, W.OS);
}
endSection(SubSection);
}
if (!InitFuncs.empty()) {
startSection(SubSection, wasm::WASM_INIT_FUNCS);
encodeULEB128(InitFuncs.size(), W.OS);
for (auto &StartFunc : InitFuncs) {
encodeULEB128(StartFunc.first, W.OS); // priority
encodeULEB128(StartFunc.second, W.OS); // function index
}
endSection(SubSection);
}
if (Comdats.size()) {
startSection(SubSection, wasm::WASM_COMDAT_INFO);
encodeULEB128(Comdats.size(), W.OS);
for (const auto &C : Comdats) {
writeString(C.first);
encodeULEB128(0, W.OS); // flags for future use
encodeULEB128(C.second.size(), W.OS);
for (const WasmComdatEntry &Entry : C.second) {