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ba9fa9fd16
teak-llvm/llvm/lib/MC/WasmObjectWriter.cpp
Sam Clegg ba9fa9fd16 [WebAssembly] Model weakly defined symbols as wasm exports 
Previously these were being included as both imports and
exports, with the import being satisfied by the export
(or some strong symbol) at runtime.  However proved
unnecessary and actually complicated linking as it meant
there was not a 1-to-1 mapping between a wasm function
/global index and a linker symbol.

Differential Revision: https://reviews.llvm.org/D38246

llvm-svn: 314245
2017-09-26 21:10:09 +00:00

1322 lines
44 KiB
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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/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmInfo.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/MCObjectFileInfo.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 {
// 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 contents of the section starts (after the header).
uint64_t ContentsOffset;
};
// 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;
SmallVector<char, 4> Data;
};
// A wasm import to be written into the import section.
struct WasmImport {
StringRef ModuleName;
StringRef FieldName;
unsigned Kind;
int32_t Type;
};
// A wasm function to be written into the function section.
struct WasmFunction {
int32_t Type;
const MCSymbolWasm *Sym;
};
// A wasm export to be written into the export section.
struct WasmExport {
StringRef FieldName;
unsigned Kind;
uint32_t Index;
};
// A wasm global to be written into the global section.
struct WasmGlobal {
wasm::ValType Type;
bool IsMutable;
bool HasImport;
uint64_t InitialValue;
uint32_t ImportIndex;
};
// 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:
return true;
default:
return false;
}
}
void print(raw_ostream &Out) const {
Out << "Off=" << Offset << ", Sym=" << *Symbol << ", Addend=" << Addend
<< ", Type=" << Type
<< ", FixupSection=" << FixupSection->getSectionName();
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
#endif
};
#if !defined(NDEBUG)
raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) {
Rel.print(OS);
return OS;
}
#endif
class WasmObjectWriter : public MCObjectWriter {
/// Helper struct for containing some precomputed information on symbols.
struct WasmSymbolData {
const MCSymbolWasm *Symbol;
StringRef Name;
// Support lexicographic sorting.
bool operator<(const WasmSymbolData &RHS) const { return Name < RHS.Name; }
};
/// The target specific Wasm writer instance.
std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter;
// Relocations for fixing up references in the code section.
std::vector<WasmRelocationEntry> CodeRelocations;
// Relocations for fixing up references in the data section.
std::vector<WasmRelocationEntry> DataRelocations;
// 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> IndirectSymbolIndices;
// Maps function/global symbols to the function/global index space.
DenseMap<const MCSymbolWasm *, uint32_t> SymbolIndices;
DenseMap<WasmFunctionType, int32_t, WasmFunctionTypeDenseMapInfo>
FunctionTypeIndices;
SmallVector<WasmFunctionType, 4> FunctionTypes;
SmallVector<WasmGlobal, 4> Globals;
unsigned NumGlobalImports = 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,
const char *Name = nullptr);
void endSection(SectionBookkeeping &Section);
public:
WasmObjectWriter(MCWasmObjectTargetWriter *MOTW, raw_pwrite_stream &OS)
: MCObjectWriter(OS, /*IsLittleEndian=*/true), TargetObjectWriter(MOTW) {}
private:
~WasmObjectWriter() override;
void reset() override {
CodeRelocations.clear();
DataRelocations.clear();
TypeIndices.clear();
SymbolIndices.clear();
IndirectSymbolIndices.clear();
FunctionTypeIndices.clear();
FunctionTypes.clear();
Globals.clear();
MCObjectWriter::reset();
NumGlobalImports = 0;
}
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;
void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
void writeString(const StringRef Str) {
encodeULEB128(Str.size(), getStream());
writeBytes(Str);
}
void writeValueType(wasm::ValType Ty) {
encodeSLEB128(int32_t(Ty), getStream());
}
void writeTypeSection(ArrayRef<WasmFunctionType> FunctionTypes);
void writeImportSection(ArrayRef<WasmImport> Imports);
void writeFunctionSection(ArrayRef<WasmFunction> Functions);
void writeTableSection(uint32_t NumElements);
void writeMemorySection(uint32_t DataSize);
void writeGlobalSection();
void writeExportSection(ArrayRef<WasmExport> Exports);
void writeElemSection(ArrayRef<uint32_t> TableElems);
void writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
ArrayRef<WasmFunction> Functions);
void writeDataSection(ArrayRef<WasmDataSegment> Segments);
void writeNameSection(ArrayRef<WasmFunction> Functions,
ArrayRef<WasmImport> Imports,
uint32_t NumFuncImports);
void writeCodeRelocSection();
void writeDataRelocSection();
void writeLinkingMetaDataSection(
ArrayRef<WasmDataSegment> Segments, uint32_t DataSize,
uint32_t DataAlignment,
SmallVector<std::pair<StringRef, uint32_t>, 4> SymbolFlags,
bool HasStackPointer, uint32_t StackPointerGlobal);
uint32_t getProvisionalValue(const WasmRelocationEntry &RelEntry);
void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
uint64_t ContentsOffset);
void writeRelocations(ArrayRef<WasmRelocationEntry> Relocations);
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,
const char *Name) {
assert((Name != nullptr) == (SectionId == wasm::WASM_SEC_CUSTOM) &&
"Only custom sections can have names");
DEBUG(dbgs() << "startSection " << SectionId << ": " << Name << "\n");
encodeULEB128(SectionId, getStream());
Section.SizeOffset = getStream().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, getStream());
// The position where the section starts, for measuring its size.
Section.ContentsOffset = getStream().tell();
// Custom sections in wasm also have a string identifier.
if (SectionId == wasm::WASM_SEC_CUSTOM) {
assert(Name);
writeString(StringRef(Name));
}
}
// 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 = getStream().tell() - Section.ContentsOffset;
if (uint32_t(Size) != Size)
report_fatal_error("section size does not fit in a uint32_t");
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);
getStream().pwrite((char *)Buffer, SizeLen, Section.SizeOffset);
}
// Emit the Wasm header.
void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
writeBytes(StringRef(wasm::WasmMagic, sizeof(wasm::WasmMagic)));
writeLE32(wasm::WasmVersion);
}
void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) {
}
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();
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;
if (SymA)
SymA->setUsedInReloc();
assert(!IsPCRel);
assert(SymA);
unsigned Type = getRelocType(Target, Fixup);
WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
DEBUG(dbgs() << "WasmReloc: " << Rec << "\n");
if (FixupSection.hasInstructions())
CodeRelocations.push_back(Rec);
else
DataRelocations.push_back(Rec);
}
// 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, since
// we have addends; it just serves to make the code more readable
// and to make standalone wasm modules directly usable.
uint32_t
WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry) {
const MCSymbolWasm *Sym = ResolveSymbol(*RelEntry.Symbol);
// For undefined symbols, use a hopefully invalid value.
if (!Sym->isDefined(/*SetUsed=*/false))
return UINT32_MAX;
uint32_t GlobalIndex = SymbolIndices[Sym];
const WasmGlobal& Global = Globals[GlobalIndex - NumGlobalImports];
uint64_t Address = Global.InitialValue + RelEntry.Addend;
// Ignore overflow. LLVM allows address arithmetic to silently wrap.
uint32_t Value = Address;
return Value;
}
static void addData(SmallVectorImpl<char> &DataBytes,
MCSectionWasm &DataSection, uint32_t &DataAlignment) {
DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment()));
DataAlignment = std::max(DataAlignment, DataSection.getAlignment());
DEBUG(errs() << "addData: " << DataSection.getSectionName() << "\n");
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)) {
DataBytes.insert(DataBytes.end(), Fill->getSize(), Fill->getValue());
} else {
const auto &DataFrag = cast<MCDataFragment>(Frag);
const SmallVectorImpl<char> &Contents = DataFrag.getContents();
DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
}
}
DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n");
}
uint32_t WasmObjectWriter::getRelocationIndexValue(
const WasmRelocationEntry &RelEntry) {
switch (RelEntry.Type) {
case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32:
if (!IndirectSymbolIndices.count(RelEntry.Symbol))
report_fatal_error("symbol not found table index space: " +
RelEntry.Symbol->getName());
return IndirectSymbolIndices[RelEntry.Symbol];
case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
if (!SymbolIndices.count(RelEntry.Symbol))
report_fatal_error("symbol not found function/global index space: " +
RelEntry.Symbol->getName());
return SymbolIndices[RelEntry.Symbol];
case 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];
default:
llvm_unreachable("invalid relocation type");
}
}
// Apply the portions of the relocation records that we can handle ourselves
// directly.
void WasmObjectWriter::applyRelocations(
ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset) {
raw_pwrite_stream &Stream = getStream();
for (const WasmRelocationEntry &RelEntry : Relocations) {
uint64_t Offset = ContentsOffset +
RelEntry.FixupSection->getSectionOffset() +
RelEntry.Offset;
DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n");
switch (RelEntry.Type) {
case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB: {
uint32_t Index = getRelocationIndexValue(RelEntry);
WritePatchableSLEB(Stream, Index, Offset);
break;
}
case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32: {
uint32_t Index = getRelocationIndexValue(RelEntry);
WriteI32(Stream, Index, Offset);
break;
}
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB: {
uint32_t Value = getProvisionalValue(RelEntry);
WritePatchableSLEB(Stream, Value, Offset);
break;
}
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB: {
uint32_t Value = getProvisionalValue(RelEntry);
WritePatchableLEB(Stream, Value, Offset);
break;
}
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32: {
uint32_t Value = getProvisionalValue(RelEntry);
WriteI32(Stream, Value, Offset);
break;
}
default:
llvm_unreachable("invalid relocation type");
}
}
}
// Write out the portions of the relocation records that the linker will
// need to handle.
void WasmObjectWriter::writeRelocations(
ArrayRef<WasmRelocationEntry> Relocations) {
raw_pwrite_stream &Stream = getStream();
for (const WasmRelocationEntry& RelEntry : Relocations) {
uint64_t Offset = RelEntry.Offset +
RelEntry.FixupSection->getSectionOffset();
uint32_t Index = getRelocationIndexValue(RelEntry);
encodeULEB128(RelEntry.Type, Stream);
encodeULEB128(Offset, Stream);
encodeULEB128(Index, Stream);
if (RelEntry.hasAddend())
encodeSLEB128(RelEntry.Addend, Stream);
}
}
void WasmObjectWriter::writeTypeSection(
ArrayRef<WasmFunctionType> FunctionTypes) {
if (FunctionTypes.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_TYPE);
encodeULEB128(FunctionTypes.size(), getStream());
for (const WasmFunctionType &FuncTy : FunctionTypes) {
encodeSLEB128(wasm::WASM_TYPE_FUNC, getStream());
encodeULEB128(FuncTy.Params.size(), getStream());
for (wasm::ValType Ty : FuncTy.Params)
writeValueType(Ty);
encodeULEB128(FuncTy.Returns.size(), getStream());
for (wasm::ValType Ty : FuncTy.Returns)
writeValueType(Ty);
}
endSection(Section);
}
void WasmObjectWriter::writeImportSection(ArrayRef<WasmImport> Imports) {
if (Imports.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_IMPORT);
encodeULEB128(Imports.size(), getStream());
for (const WasmImport &Import : Imports) {
writeString(Import.ModuleName);
writeString(Import.FieldName);
encodeULEB128(Import.Kind, getStream());
switch (Import.Kind) {
case wasm::WASM_EXTERNAL_FUNCTION:
encodeULEB128(Import.Type, getStream());
break;
case wasm::WASM_EXTERNAL_GLOBAL:
encodeSLEB128(int32_t(Import.Type), getStream());
encodeULEB128(0, getStream()); // mutability
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(), getStream());
for (const WasmFunction &Func : Functions)
encodeULEB128(Func.Type, getStream());
endSection(Section);
}
void WasmObjectWriter::writeTableSection(uint32_t NumElements) {
// For now, always emit the table section, since indirect calls are not
// valid without it. In the future, we could perhaps be more clever and omit
// it if there are no indirect calls.
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_TABLE);
encodeULEB128(1, getStream()); // The number of tables.
// Fixed to 1 for now.
encodeSLEB128(wasm::WASM_TYPE_ANYFUNC, getStream()); // Type of table
encodeULEB128(0, getStream()); // flags
encodeULEB128(NumElements, getStream()); // initial
endSection(Section);
}
void WasmObjectWriter::writeMemorySection(uint32_t DataSize) {
// For now, always emit the memory section, since loads and stores are not
// valid without it. In the future, we could perhaps be more clever and omit
// it if there are no loads or stores.
SectionBookkeeping Section;
uint32_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize;
startSection(Section, wasm::WASM_SEC_MEMORY);
encodeULEB128(1, getStream()); // number of memory spaces
encodeULEB128(0, getStream()); // flags
encodeULEB128(NumPages, getStream()); // initial
endSection(Section);
}
void WasmObjectWriter::writeGlobalSection() {
if (Globals.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_GLOBAL);
encodeULEB128(Globals.size(), getStream());
for (const WasmGlobal &Global : Globals) {
writeValueType(Global.Type);
write8(Global.IsMutable);
if (Global.HasImport) {
assert(Global.InitialValue == 0);
write8(wasm::WASM_OPCODE_GET_GLOBAL);
encodeULEB128(Global.ImportIndex, getStream());
} else {
assert(Global.ImportIndex == 0);
write8(wasm::WASM_OPCODE_I32_CONST);
encodeSLEB128(Global.InitialValue, getStream()); // offset
}
write8(wasm::WASM_OPCODE_END);
}
endSection(Section);
}
void WasmObjectWriter::writeExportSection(ArrayRef<WasmExport> Exports) {
if (Exports.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_EXPORT);
encodeULEB128(Exports.size(), getStream());
for (const WasmExport &Export : Exports) {
writeString(Export.FieldName);
encodeSLEB128(Export.Kind, getStream());
encodeULEB128(Export.Index, getStream());
}
endSection(Section);
}
void WasmObjectWriter::writeElemSection(ArrayRef<uint32_t> TableElems) {
if (TableElems.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_ELEM);
encodeULEB128(1, getStream()); // number of "segments"
encodeULEB128(0, getStream()); // the table index
// init expr for starting offset
write8(wasm::WASM_OPCODE_I32_CONST);
encodeSLEB128(0, getStream());
write8(wasm::WASM_OPCODE_END);
encodeULEB128(TableElems.size(), getStream());
for (uint32_t Elem : TableElems)
encodeULEB128(Elem, getStream());
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);
encodeULEB128(Functions.size(), getStream());
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, getStream());
FuncSection.setSectionOffset(getStream().tell() - Section.ContentsOffset);
Asm.writeSectionData(&FuncSection, Layout);
}
// Apply fixups.
applyRelocations(CodeRelocations, Section.ContentsOffset);
endSection(Section);
}
void WasmObjectWriter::writeDataSection(ArrayRef<WasmDataSegment> Segments) {
if (Segments.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_DATA);
encodeULEB128(Segments.size(), getStream()); // count
for (const WasmDataSegment & Segment : Segments) {
encodeULEB128(0, getStream()); // memory index
write8(wasm::WASM_OPCODE_I32_CONST);
encodeSLEB128(Segment.Offset, getStream()); // offset
write8(wasm::WASM_OPCODE_END);
encodeULEB128(Segment.Data.size(), getStream()); // size
Segment.Section->setSectionOffset(getStream().tell() - Section.ContentsOffset);
writeBytes(Segment.Data); // data
}
// Apply fixups.
applyRelocations(DataRelocations, Section.ContentsOffset);
endSection(Section);
}
void WasmObjectWriter::writeNameSection(
ArrayRef<WasmFunction> Functions,
ArrayRef<WasmImport> Imports,
unsigned NumFuncImports) {
uint32_t TotalFunctions = NumFuncImports + Functions.size();
if (TotalFunctions == 0)
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_CUSTOM, "name");
SectionBookkeeping SubSection;
startSection(SubSection, wasm::WASM_NAMES_FUNCTION);
encodeULEB128(TotalFunctions, getStream());
uint32_t Index = 0;
for (const WasmImport &Import : Imports) {
if (Import.Kind == wasm::WASM_EXTERNAL_FUNCTION) {
encodeULEB128(Index, getStream());
writeString(Import.FieldName);
++Index;
}
}
for (const WasmFunction &Func : Functions) {
encodeULEB128(Index, getStream());
writeString(Func.Sym->getName());
++Index;
}
endSection(SubSection);
endSection(Section);
}
void WasmObjectWriter::writeCodeRelocSection() {
// See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
// for descriptions of the reloc sections.
if (CodeRelocations.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_CUSTOM, "reloc.CODE");
encodeULEB128(wasm::WASM_SEC_CODE, getStream());
encodeULEB128(CodeRelocations.size(), getStream());
writeRelocations(CodeRelocations);
endSection(Section);
}
void WasmObjectWriter::writeDataRelocSection() {
// See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
// for descriptions of the reloc sections.
if (DataRelocations.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_CUSTOM, "reloc.DATA");
encodeULEB128(wasm::WASM_SEC_DATA, getStream());
encodeULEB128(DataRelocations.size(), getStream());
writeRelocations(DataRelocations);
endSection(Section);
}
void WasmObjectWriter::writeLinkingMetaDataSection(
ArrayRef<WasmDataSegment> Segments, uint32_t DataSize,
uint32_t DataAlignment,
SmallVector<std::pair<StringRef, uint32_t>, 4> SymbolFlags,
bool HasStackPointer, uint32_t StackPointerGlobal) {
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_CUSTOM, "linking");
SectionBookkeeping SubSection;
if (HasStackPointer) {
startSection(SubSection, wasm::WASM_STACK_POINTER);
encodeULEB128(StackPointerGlobal, getStream()); // id
endSection(SubSection);
}
if (SymbolFlags.size() != 0) {
startSection(SubSection, wasm::WASM_SYMBOL_INFO);
encodeULEB128(SymbolFlags.size(), getStream());
for (auto Pair: SymbolFlags) {
writeString(Pair.first);
encodeULEB128(Pair.second, getStream());
}
endSection(SubSection);
}
if (DataSize > 0) {
startSection(SubSection, wasm::WASM_DATA_SIZE);
encodeULEB128(DataSize, getStream());
endSection(SubSection);
startSection(SubSection, wasm::WASM_DATA_ALIGNMENT);
encodeULEB128(DataAlignment, getStream());
endSection(SubSection);
}
if (Segments.size()) {
startSection(SubSection, wasm::WASM_SEGMENT_NAMES);
encodeULEB128(Segments.size(), getStream());
for (const WasmDataSegment &Segment : Segments)
writeString(Segment.Name);
endSection(SubSection);
}
endSection(Section);
}
uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm& Symbol) {
assert(Symbol.isFunction());
assert(TypeIndices.count(&Symbol));
return TypeIndices[&Symbol];
}
uint32_t WasmObjectWriter::registerFunctionType(const MCSymbolWasm& Symbol) {
assert(Symbol.isFunction());
WasmFunctionType F;
const MCSymbolWasm* ResolvedSym = ResolveSymbol(Symbol);
F.Returns = ResolvedSym->getReturns();
F.Params = ResolvedSym->getParams();
auto Pair =
FunctionTypeIndices.insert(std::make_pair(F, FunctionTypes.size()));
if (Pair.second)
FunctionTypes.push_back(F);
TypeIndices[&Symbol] = Pair.first->second;
DEBUG(dbgs() << "registerFunctionType: " << Symbol << " new:" << Pair.second << "\n");
DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n");
return Pair.first->second;
}
void WasmObjectWriter::writeObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
DEBUG(dbgs() << "WasmObjectWriter::writeObject\n");
MCContext &Ctx = Asm.getContext();
wasm::ValType PtrType = is64Bit() ? wasm::ValType::I64 : wasm::ValType::I32;
// Collect information from the available symbols.
SmallVector<WasmFunction, 4> Functions;
SmallVector<uint32_t, 4> TableElems;
SmallVector<WasmImport, 4> Imports;
SmallVector<WasmExport, 4> Exports;
SmallVector<std::pair<StringRef, uint32_t>, 4> SymbolFlags;
SmallPtrSet<const MCSymbolWasm *, 4> IsAddressTaken;
unsigned NumFuncImports = 0;
SmallVector<WasmDataSegment, 4> DataSegments;
uint32_t DataAlignment = 1;
uint32_t StackPointerGlobal = 0;
uint32_t DataSize = 0;
bool HasStackPointer = false;
// Populate the IsAddressTaken set.
for (const WasmRelocationEntry &RelEntry : CodeRelocations) {
switch (RelEntry.Type) {
case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
IsAddressTaken.insert(RelEntry.Symbol);
break;
default:
break;
}
}
for (const WasmRelocationEntry &RelEntry : DataRelocations) {
switch (RelEntry.Type) {
case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32:
case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
IsAddressTaken.insert(RelEntry.Symbol);
break;
default:
break;
}
}
// Populate FunctionTypeIndices and Imports.
for (const MCSymbol &S : Asm.symbols()) {
const auto &WS = static_cast<const MCSymbolWasm &>(S);
if (WS.isTemporary())
continue;
if (WS.isFunction())
registerFunctionType(WS);
// If the symbol is not defined in this translation unit, import it.
if (!WS.isDefined(/*SetUsed=*/false)) {
WasmImport Import;
Import.ModuleName = WS.getModuleName();
Import.FieldName = WS.getName();
if (WS.isFunction()) {
Import.Kind = wasm::WASM_EXTERNAL_FUNCTION;
Import.Type = getFunctionType(WS);
SymbolIndices[&WS] = NumFuncImports;
++NumFuncImports;
} else {
Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
Import.Type = int32_t(PtrType);
SymbolIndices[&WS] = NumGlobalImports;
++NumGlobalImports;
}
Imports.push_back(Import);
}
}
// In the special .global_variables section, we've encoded global
// variables used by the function. Translate them into the Globals
// list.
MCSectionWasm *GlobalVars = Ctx.getWasmSection(".global_variables", wasm::WASM_SEC_DATA);
if (!GlobalVars->getFragmentList().empty()) {
if (GlobalVars->getFragmentList().size() != 1)
report_fatal_error("only one .global_variables fragment supported");
const MCFragment &Frag = *GlobalVars->begin();
if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
report_fatal_error("only data supported in .global_variables");
const auto &DataFrag = cast<MCDataFragment>(Frag);
if (!DataFrag.getFixups().empty())
report_fatal_error("fixups not supported in .global_variables");
const SmallVectorImpl<char> &Contents = DataFrag.getContents();
for (const uint8_t *p = (const uint8_t *)Contents.data(),
*end = (const uint8_t *)Contents.data() + Contents.size();
p != end; ) {
WasmGlobal G;
if (end - p < 3)
report_fatal_error("truncated global variable encoding");
G.Type = wasm::ValType(int8_t(*p++));
G.IsMutable = bool(*p++);
G.HasImport = bool(*p++);
if (G.HasImport) {
G.InitialValue = 0;
WasmImport Import;
Import.ModuleName = (const char *)p;
const uint8_t *nul = (const uint8_t *)memchr(p, '\0', end - p);
if (!nul)
report_fatal_error("global module name must be nul-terminated");
p = nul + 1;
nul = (const uint8_t *)memchr(p, '\0', end - p);
if (!nul)
report_fatal_error("global base name must be nul-terminated");
Import.FieldName = (const char *)p;
p = nul + 1;
Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
Import.Type = int32_t(G.Type);
G.ImportIndex = NumGlobalImports;
++NumGlobalImports;
Imports.push_back(Import);
} else {
unsigned n;
G.InitialValue = decodeSLEB128(p, &n);
G.ImportIndex = 0;
if ((ptrdiff_t)n > end - p)
report_fatal_error("global initial value must be valid SLEB128");
p += n;
}
Globals.push_back(G);
}
}
// In the special .stack_pointer section, we've encoded the stack pointer
// index.
MCSectionWasm *StackPtr = Ctx.getWasmSection(".stack_pointer", wasm::WASM_SEC_DATA);
if (!StackPtr->getFragmentList().empty()) {
if (StackPtr->getFragmentList().size() != 1)
report_fatal_error("only one .stack_pointer fragment supported");
const MCFragment &Frag = *StackPtr->begin();
if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
report_fatal_error("only data supported in .stack_pointer");
const auto &DataFrag = cast<MCDataFragment>(Frag);
if (!DataFrag.getFixups().empty())
report_fatal_error("fixups not supported in .stack_pointer");
const SmallVectorImpl<char> &Contents = DataFrag.getContents();
if (Contents.size() != 4)
report_fatal_error("only one entry supported in .stack_pointer");
HasStackPointer = true;
StackPointerGlobal = NumGlobalImports + *(const int32_t *)Contents.data();
}
for (MCSection &Sec : Asm) {
auto &Section = static_cast<MCSectionWasm &>(Sec);
if (Section.getType() != wasm::WASM_SEC_DATA)
continue;
DataSize = alignTo(DataSize, Section.getAlignment());
DataSegments.emplace_back();
WasmDataSegment &Segment = DataSegments.back();
Segment.Name = Section.getSectionName();
Segment.Offset = DataSize;
Segment.Section = &Section;
addData(Segment.Data, Section, DataAlignment);
DataSize += Segment.Data.size();
Section.setMemoryOffset(Segment.Offset);
}
// Handle regular defined and undefined symbols.
for (const MCSymbol &S : Asm.symbols()) {
// Ignore unnamed temporary symbols, which aren't ever exported, imported,
// or used in relocations.
if (S.isTemporary() && S.getName().empty())
continue;
const auto &WS = static_cast<const MCSymbolWasm &>(S);
DEBUG(dbgs() << "MCSymbol: '" << S << "'"
<< " isDefined=" << S.isDefined() << " isExternal="
<< S.isExternal() << " isTemporary=" << S.isTemporary()
<< " isFunction=" << WS.isFunction()
<< " isWeak=" << WS.isWeak()
<< " isVariable=" << WS.isVariable() << "\n");
if (WS.isWeak())
SymbolFlags.emplace_back(WS.getName(), wasm::WASM_SYMBOL_BINDING_WEAK);
if (WS.isVariable())
continue;
unsigned Index;
if (WS.isFunction()) {
if (WS.isDefined(/*SetUsed=*/false)) {
if (WS.getOffset() != 0)
report_fatal_error(
"function sections must contain one function each");
if (WS.getSize() == 0)
report_fatal_error(
"function symbols must have a size set with .size");
// A definition. Take the next available index.
Index = NumFuncImports + Functions.size();
// Prepare the function.
WasmFunction Func;
Func.Type = getFunctionType(WS);
Func.Sym = &WS;
SymbolIndices[&WS] = Index;
Functions.push_back(Func);
} else {
// An import; the index was assigned above.
Index = SymbolIndices.find(&WS)->second;
}
DEBUG(dbgs() << " -> function index: " << Index << "\n");
// If needed, prepare the function to be called indirectly.
if (IsAddressTaken.count(&WS) != 0) {
IndirectSymbolIndices[&WS] = TableElems.size();
DEBUG(dbgs() << " -> adding to table: " << TableElems.size() << "\n");
TableElems.push_back(Index);
}
} else {
if (WS.isTemporary() && !WS.getSize())
continue;
if (!WS.isDefined(/*SetUsed=*/false))
continue;
if (!WS.getSize())
report_fatal_error("data symbols must have a size set with .size: " +
WS.getName());
int64_t Size = 0;
if (!WS.getSize()->evaluateAsAbsolute(Size, Layout))
report_fatal_error(".size expression must be evaluatable");
// For each global, prepare a corresponding wasm global holding its
// address. For externals these will also be named exports.
Index = NumGlobalImports + Globals.size();
auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
WasmGlobal Global;
Global.Type = PtrType;
Global.IsMutable = false;
Global.HasImport = false;
Global.InitialValue = DataSection.getMemoryOffset() + Layout.getSymbolOffset(WS);
Global.ImportIndex = 0;
SymbolIndices[&WS] = Index;
DEBUG(dbgs() << " -> global index: " << Index << "\n");
Globals.push_back(Global);
}
// If the symbol is visible outside this translation unit, export it.
if (WS.isDefined(/*SetUsed=*/false)) {
WasmExport Export;
Export.FieldName = WS.getName();
Export.Index = Index;
if (WS.isFunction())
Export.Kind = wasm::WASM_EXTERNAL_FUNCTION;
else
Export.Kind = wasm::WASM_EXTERNAL_GLOBAL;
DEBUG(dbgs() << " -> export " << Exports.size() << "\n");
Exports.push_back(Export);
if (!WS.isExternal())
SymbolFlags.emplace_back(WS.getName(), wasm::WASM_SYMBOL_BINDING_LOCAL);
}
}
// Handle weak aliases. We need to process these in a separate pass because
// we need to have processed the target of the alias before the alias itself
// and the symbols are not necessarily ordered in this way.
for (const MCSymbol &S : Asm.symbols()) {
if (!S.isVariable())
continue;
assert(S.isDefined(/*SetUsed=*/false));
// Find the target symbol of this weak alias and export that index
const auto &WS = static_cast<const MCSymbolWasm &>(S);
const MCSymbolWasm *ResolvedSym = ResolveSymbol(WS);
DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *ResolvedSym << "'\n");
assert(SymbolIndices.count(ResolvedSym) > 0);
uint32_t Index = SymbolIndices.find(ResolvedSym)->second;
DEBUG(dbgs() << " -> index:" << Index << "\n");
SymbolIndices[&WS] = Index;
WasmExport Export;
Export.FieldName = WS.getName();
Export.Index = Index;
if (WS.isFunction())
Export.Kind = wasm::WASM_EXTERNAL_FUNCTION;
else
Export.Kind = wasm::WASM_EXTERNAL_GLOBAL;
DEBUG(dbgs() << " -> export " << Exports.size() << "\n");
Exports.push_back(Export);
if (!WS.isExternal())
SymbolFlags.emplace_back(WS.getName(), wasm::WASM_SYMBOL_BINDING_LOCAL);
}
// Add types for indirect function calls.
for (const WasmRelocationEntry &Fixup : CodeRelocations) {
if (Fixup.Type != wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB)
continue;
registerFunctionType(*Fixup.Symbol);
}
// Write out the Wasm header.
writeHeader(Asm);
writeTypeSection(FunctionTypes);
writeImportSection(Imports);
writeFunctionSection(Functions);
writeTableSection(TableElems.size());
writeMemorySection(DataSize);
writeGlobalSection();
writeExportSection(Exports);
// TODO: Start Section
writeElemSection(TableElems);
writeCodeSection(Asm, Layout, Functions);
writeDataSection(DataSegments);
writeNameSection(Functions, Imports, NumFuncImports);
writeCodeRelocSection();
writeDataRelocSection();
writeLinkingMetaDataSection(DataSegments, DataSize, DataAlignment,
SymbolFlags, HasStackPointer, StackPointerGlobal);
// TODO: Translate the .comment section to the output.
// TODO: Translate debug sections to the output.
}
MCObjectWriter *llvm::createWasmObjectWriter(MCWasmObjectTargetWriter *MOTW,
raw_pwrite_stream &OS) {
return new WasmObjectWriter(MOTW, OS);
}
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