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llvm-mirror/lib/MC/WasmObjectWriter.cpp
Thomas Lively e539ec198a [WebAssembly] Target features section 
Summary:
Implements a new target features section in assembly and object files
that records what features are used, required, and disallowed in
WebAssembly objects. The linker uses this information to ensure that
all objects participating in a link are feature-compatible and records
the set of used features in the output binary for use by optimizers
and other tools later in the toolchain.

The "atomics" feature is always required or disallowed to prevent
linking code with stripped atomics into multithreaded binaries. Other
features are marked used if they are enabled globally or on any
function in a module.

Future CLs will add linker flags for ignoring feature compatibility
checks and for specifying the set of allowed features, implement using
the presence of the "atomics" feature to control the type of memory
and segments in the linked binary, and add front-end flags for
relaxing the linkage policy for atomics.

Reviewers: aheejin, sbc100, dschuff

Subscribers: jgravelle-google, hiraditya, sunfish, mgrang, jfb, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59173

llvm-svn: 356610
2019-03-20 20:26:45 +00:00

1615 lines
56 KiB
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//===- lib/MC/WasmObjectWriter.cpp - Wasm File Writer ---------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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 InitialTableOffset = 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 or event, in a struct capable of being used
// as a DenseMap key.
// TODO: Consider using wasm::WasmSignature directly instead.
struct WasmSignature {
// Support empty and tombstone instances, needed by DenseMap.
enum { Plain, Empty, Tombstone } State = Plain;
// The return types of the function.
SmallVector<wasm::ValType, 1> Returns;
// The parameter types of the function.
SmallVector<wasm::ValType, 4> Params;
bool operator==(const WasmSignature &Other) const {
return State == Other.State && Returns == Other.Returns &&
Params == Other.Params;
}
};
// Traits for using WasmSignature in a DenseMap.
struct WasmSignatureDenseMapInfo {
static WasmSignature getEmptyKey() {
WasmSignature Sig;
Sig.State = WasmSignature::Empty;
return Sig;
}
static WasmSignature getTombstoneKey() {
WasmSignature Sig;
Sig.State = WasmSignature::Tombstone;
return Sig;
}
static unsigned getHashValue(const WasmSignature &Sig) {
uintptr_t Value = Sig.State;
for (wasm::ValType Ret : Sig.Returns)
Value += DenseMapInfo<uint32_t>::getHashValue(uint32_t(Ret));
for (wasm::ValType Param : Sig.Params)
Value += DenseMapInfo<uint32_t>::getHashValue(uint32_t(Param));
return Value;
}
static bool isEqual(const WasmSignature &LHS, const WasmSignature &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 InitFlags;
uint32_t Offset;
uint32_t Alignment;
uint32_t LinkerFlags;
SmallVector<char, 4> Data;
};
// A wasm function to be written into the function section.
struct WasmFunction {
uint32_t SigIndex;
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_WASM_MEMORY_ADDR_LEB:
case wasm::R_WASM_MEMORY_ADDR_SLEB:
case wasm::R_WASM_MEMORY_ADDR_I32:
case wasm::R_WASM_FUNCTION_OFFSET_I32:
case wasm::R_WASM_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 InvalidIndex = -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(InvalidIndex) {}
};
#if !defined(NDEBUG)
raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) {
Rel.print(OS);
return OS;
}
#endif
// 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);
}
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/event/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;
std::unique_ptr<WasmCustomSection> ProducersSection;
std::unique_ptr<WasmCustomSection> TargetFeaturesSection;
// 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<WasmSignature, uint32_t, WasmSignatureDenseMapInfo> SignatureIndices;
SmallVector<WasmSignature, 4> Signatures;
SmallVector<WasmGlobal, 4> Globals;
SmallVector<WasmDataSegment, 4> DataSegments;
unsigned NumFunctionImports = 0;
unsigned NumGlobalImports = 0;
unsigned NumEventImports = 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)) {}
private:
void reset() override {
CodeRelocations.clear();
DataRelocations.clear();
TypeIndices.clear();
WasmIndices.clear();
TableIndices.clear();
DataLocations.clear();
CustomSections.clear();
ProducersSection.reset();
TargetFeaturesSection.reset();
CustomSectionsRelocations.clear();
SignatureIndices.clear();
Signatures.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<WasmSignature> Signatures);
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 writeEventSection(ArrayRef<wasm::WasmEventType> Events);
void writeRelocSection(uint32_t SectionIndex, StringRef Name,
std::vector<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 writeCustomSection(WasmCustomSection &CustomSection,
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 getEventType(const MCSymbolWasm &Symbol);
void registerFunctionType(const MCSymbolWasm &Symbol);
void registerEventType(const MCSymbolWasm &Symbol);
};
} // end anonymous namespace
// 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(0, W.OS, 5);
// 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();
// /dev/null doesn't support seek/tell and can report offset of 0.
// Simply skip this patching in that case.
if (!Size)
return;
Size -= 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.
writePatchableLEB(static_cast<raw_pwrite_stream &>(W.OS), Size,
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_WASM_FUNCTION_OFFSET_I32 ||
Type == wasm::R_WASM_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_WASM_TYPE_INDEX_LEB are required to be
// against a named symbol.
if (Type != wasm::R_WASM_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");
}
}
static const MCSymbolWasm *resolveSymbol(const MCSymbolWasm &Symbol) {
const MCSymbolWasm* Ret = &Symbol;
while (Ret->isVariable()) {
const MCExpr *Expr = Ret->getVariableValue();
auto *Inner = cast<MCSymbolRefExpr>(Expr);
Ret = cast<MCSymbolWasm>(&Inner->getSymbol());
}
return Ret;
}
// 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_WASM_TABLE_INDEX_SLEB:
case wasm::R_WASM_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_WASM_TYPE_INDEX_LEB:
// Provisional value is same as the index
return getRelocationIndexValue(RelEntry);
case wasm::R_WASM_FUNCTION_INDEX_LEB:
case wasm::R_WASM_GLOBAL_INDEX_LEB:
case wasm::R_WASM_EVENT_INDEX_LEB:
// Provisional value is function/global/event 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_WASM_FUNCTION_OFFSET_I32:
case wasm::R_WASM_SECTION_OFFSET_I32: {
const auto &Section =
static_cast<const MCSectionWasm &>(RelEntry.Symbol->getSection());
return Section.getSectionOffset() + RelEntry.Addend;
}
case wasm::R_WASM_MEMORY_ADDR_LEB:
case wasm::R_WASM_MEMORY_ADDR_I32:
case wasm::R_WASM_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 if (auto *LEB = dyn_cast<MCLEBFragment>(&Frag)) {
const SmallVectorImpl<char> &Contents = LEB->getContents();
DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
} 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_WASM_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_WASM_FUNCTION_INDEX_LEB:
case wasm::R_WASM_TYPE_INDEX_LEB:
case wasm::R_WASM_GLOBAL_INDEX_LEB:
case wasm::R_WASM_MEMORY_ADDR_LEB:
case wasm::R_WASM_EVENT_INDEX_LEB:
writePatchableLEB(Stream, Value, Offset);
break;
case wasm::R_WASM_TABLE_INDEX_I32:
case wasm::R_WASM_MEMORY_ADDR_I32:
case wasm::R_WASM_FUNCTION_OFFSET_I32:
case wasm::R_WASM_SECTION_OFFSET_I32:
writeI32(Stream, Value, Offset);
break;
case wasm::R_WASM_TABLE_INDEX_SLEB:
case wasm::R_WASM_MEMORY_ADDR_SLEB:
writePatchableSLEB(Stream, Value, Offset);
break;
default:
llvm_unreachable("invalid relocation type");
}
}
}
void WasmObjectWriter::writeTypeSection(ArrayRef<WasmSignature> Signatures) {
if (Signatures.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_TYPE);
encodeULEB128(Signatures.size(), W.OS);
for (const WasmSignature &Sig : Signatures) {
W.OS << char(wasm::WASM_TYPE_FUNC);
encodeULEB128(Sig.Params.size(), W.OS);
for (wasm::ValType Ty : Sig.Params)
writeValueType(Ty);
encodeULEB128(Sig.Returns.size(), W.OS);
for (wasm::ValType Ty : Sig.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;
case wasm::WASM_EXTERNAL_EVENT:
encodeULEB128(Import.Event.Attribute, W.OS);
encodeULEB128(Import.Event.SigIndex, W.OS);
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.SigIndex, 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::writeEventSection(ArrayRef<wasm::WasmEventType> Events) {
if (Events.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_EVENT);
encodeULEB128(Events.size(), W.OS);
for (const wasm::WasmEventType &Event : Events) {
encodeULEB128(Event.Attribute, W.OS);
encodeULEB128(Event.SigIndex, W.OS);
}
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(InitialTableOffset, 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(Segment.InitFlags, W.OS); // flags
if (Segment.InitFlags & wasm::WASM_SEGMENT_HAS_MEMINDEX)
encodeULEB128(0, W.OS); // memory index
if ((Segment.InitFlags & wasm::WASM_SEGMENT_IS_PASSIVE) == 0) {
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,
std::vector<WasmRelocationEntry> &Relocs) {
// See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
// for descriptions of the reloc sections.
if (Relocs.empty())
return;
// First, ensure the relocations are sorted in offset order. In general they
// should already be sorted since `recordRelocation` is called in offset
// order, but for the code section we combine many MC sections into single
// wasm section, and this order is determined by the order of Asm.Symbols()
// not the sections order.
std::stable_sort(
Relocs.begin(), Relocs.end(),
[](const WasmRelocationEntry &A, const WasmRelocationEntry &B) {
return (A.Offset + A.FixupSection->getSectionOffset()) <
(B.Offset + B.FixupSection->getSectionOffset());
});
SectionBookkeeping Section;
startCustomSection(Section, std::string("reloc.") + Name.str());
encodeULEB128(SectionIndex, W.OS);
encodeULEB128(Relocs.size(), W.OS);
for (const WasmRelocationEntry &RelEntry : Relocs) {
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:
case wasm::WASM_SYMBOL_TYPE_EVENT:
encodeULEB128(Sym.ElementIndex, W.OS);
if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0 ||
(Sym.Flags & wasm::WASM_SYMBOL_EXPLICIT_NAME) != 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.LinkerFlags, 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) {
encodeULEB128(Entry.Kind, W.OS);
encodeULEB128(Entry.Index, W.OS);
}
}
endSection(SubSection);
}
endSection(Section);
}
void WasmObjectWriter::writeCustomSection(WasmCustomSection &CustomSection,
const MCAssembler &Asm,
const MCAsmLayout &Layout) {
SectionBookkeeping Section;
auto *Sec = CustomSection.Section;
startCustomSection(Section, CustomSection.Name);
Sec->setSectionOffset(W.OS.tell() - Section.ContentsOffset);
Asm.writeSectionData(W.OS, Sec, Layout);
CustomSection.OutputContentsOffset = Section.ContentsOffset;
CustomSection.OutputIndex = Section.Index;
endSection(Section);
// Apply fixups.
auto &Relocations = CustomSectionsRelocations[CustomSection.Section];
applyRelocations(Relocations, CustomSection.OutputContentsOffset);
}
uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm &Symbol) {
assert(Symbol.isFunction());
assert(TypeIndices.count(&Symbol));
return TypeIndices[&Symbol];
}
uint32_t WasmObjectWriter::getEventType(const MCSymbolWasm &Symbol) {
assert(Symbol.isEvent());
assert(TypeIndices.count(&Symbol));
return TypeIndices[&Symbol];
}
void WasmObjectWriter::registerFunctionType(const MCSymbolWasm &Symbol) {
assert(Symbol.isFunction());
WasmSignature S;
const MCSymbolWasm *ResolvedSym = resolveSymbol(Symbol);
if (auto *Sig = ResolvedSym->getSignature()) {
S.Returns = Sig->Returns;
S.Params = Sig->Params;
}
auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size()));
if (Pair.second)
Signatures.push_back(S);
TypeIndices[&Symbol] = Pair.first->second;
LLVM_DEBUG(dbgs() << "registerFunctionType: " << Symbol
<< " new:" << Pair.second << "\n");
LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n");
}
void WasmObjectWriter::registerEventType(const MCSymbolWasm &Symbol) {
assert(Symbol.isEvent());
// TODO Currently we don't generate imported exceptions, but if we do, we
// should have a way of infering types of imported exceptions.
WasmSignature S;
if (auto *Sig = Symbol.getSignature()) {
S.Returns = Sig->Returns;
S.Params = Sig->Params;
}
auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size()));
if (Pair.second)
Signatures.push_back(S);
TypeIndices[&Symbol] = Pair.first->second;
LLVM_DEBUG(dbgs() << "registerEventType: " << Symbol << " new:" << Pair.second
<< "\n");
LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n");
}
static bool isInSymtab(const MCSymbolWasm &Sym) {
if (Sym.isUsedInReloc())
return true;
if (Sym.isComdat() && !Sym.isDefined())
return false;
if (Sym.isTemporary() && Sym.getName().empty())
return false;
if (Sym.isTemporary() && Sym.isData() && !Sym.getSize())
return false;
if (Sym.isSection())
return false;
return true;
}
uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
uint64_t StartOffset = W.OS.tell();
LLVM_DEBUG(dbgs() << "WasmObjectWriter::writeObject\n");
// Collect information from the available symbols.
SmallVector<WasmFunction, 4> Functions;
SmallVector<uint32_t, 4> TableElems;
SmallVector<wasm::WasmImport, 4> Imports;
SmallVector<wasm::WasmExport, 4> Exports;
SmallVector<wasm::WasmEventType, 1> Events;
SmallVector<wasm::WasmSymbolInfo, 4> SymbolInfos;
SmallVector<std::pair<uint16_t, uint32_t>, 2> InitFuncs;
std::map<StringRef, std::vector<WasmComdatEntry>> Comdats;
uint32_t DataSize = 0;
// For now, always emit the memory import, 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.
wasm::WasmImport MemImport;
MemImport.Module = "env";
MemImport.Field = "__linear_memory";
MemImport.Kind = wasm::WASM_EXTERNAL_MEMORY;
Imports.push_back(MemImport);
// 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.
wasm::WasmImport TableImport;
TableImport.Module = "env";
TableImport.Field = "__indirect_function_table";
TableImport.Kind = wasm::WASM_EXTERNAL_TABLE;
TableImport.Table.ElemType = wasm::WASM_TYPE_FUNCREF;
Imports.push_back(TableImport);
// Populate SignatureIndices, and Imports and WasmIndices for undefined
// symbols. This must be done before populating WasmIndices for defined
// symbols.
for (const MCSymbol &S : Asm.symbols()) {
const auto &WS = static_cast<const MCSymbolWasm &>(S);
// Register types for all functions, including those with private linkage
// (because wasm always needs a type signature).
if (WS.isFunction())
registerFunctionType(WS);
if (WS.isEvent())
registerEventType(WS);
if (WS.isTemporary())
continue;
// If the symbol is not defined in this translation unit, import it.
if (!WS.isDefined() && !WS.isComdat()) {
if (WS.isFunction()) {
wasm::WasmImport Import;
Import.Module = WS.getImportModule();
Import.Field = WS.getImportName();
Import.Kind = wasm::WASM_EXTERNAL_FUNCTION;
Import.SigIndex = getFunctionType(WS);
Imports.push_back(Import);
WasmIndices[&WS] = NumFunctionImports++;
} else if (WS.isGlobal()) {
if (WS.isWeak())
report_fatal_error("undefined global symbol cannot be weak");
wasm::WasmImport Import;
Import.Module = WS.getImportModule();
Import.Field = WS.getImportName();
Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
Import.Global = WS.getGlobalType();
Imports.push_back(Import);
WasmIndices[&WS] = NumGlobalImports++;
} else if (WS.isEvent()) {
if (WS.isWeak())
report_fatal_error("undefined event symbol cannot be weak");
wasm::WasmImport Import;
Import.Module = WS.getImportModule();
Import.Field = WS.getImportName();
Import.Kind = wasm::WASM_EXTERNAL_EVENT;
Import.Event.Attribute = wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION;
Import.Event.SigIndex = getEventType(WS);
Imports.push_back(Import);
WasmIndices[&WS] = NumEventImports++;
}
}
}
// Populate DataSegments and CustomSections, which must be done before
// populating DataLocations.
for (MCSection &Sec : Asm) {
auto &Section = static_cast<MCSectionWasm &>(Sec);
StringRef SectionName = Section.getSectionName();
// .init_array sections are handled specially elsewhere.
if (SectionName.startswith(".init_array"))
continue;
// Code is handled separately
if (Section.getKind().isText())
continue;
if (Section.isWasmData()) {
uint32_t SegmentIndex = DataSegments.size();
DataSize = alignTo(DataSize, Section.getAlignment());
DataSegments.emplace_back();
WasmDataSegment &Segment = DataSegments.back();
Segment.Name = SectionName;
Segment.InitFlags =
Section.getPassive() ? (uint32_t)wasm::WASM_SEGMENT_IS_PASSIVE : 0;
Segment.Offset = DataSize;
Segment.Section = &Section;
addData(Segment.Data, Section);
Segment.Alignment = Log2_32(Section.getAlignment());
Segment.LinkerFlags = 0;
DataSize += Segment.Data.size();
Section.setSegmentIndex(SegmentIndex);
if (const MCSymbolWasm *C = Section.getGroup()) {
Comdats[C->getName()].emplace_back(
WasmComdatEntry{wasm::WASM_COMDAT_DATA, SegmentIndex});
}
} else {
// Create custom sections
assert(Sec.getKind().isMetadata());
StringRef Name = SectionName;
// For user-defined custom sections, strip the prefix
if (Name.startswith(".custom_section."))
Name = Name.substr(strlen(".custom_section."));
MCSymbol *Begin = Sec.getBeginSymbol();
if (Begin) {
WasmIndices[cast<MCSymbolWasm>(Begin)] = CustomSections.size();
if (SectionName != Begin->getName())
report_fatal_error("section name and begin symbol should match: " +
Twine(SectionName));
}
// Separate out the producers and target features sections
if (Name == "producers") {
ProducersSection = llvm::make_unique<WasmCustomSection>(Name, &Section);
continue;
}
if (Name == "target_features") {
TargetFeaturesSection =
llvm::make_unique<WasmCustomSection>(Name, &Section);
continue;
}
CustomSections.emplace_back(Name, &Section);
}
}
// Populate WasmIndices and DataLocations for defined 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);
LLVM_DEBUG(
dbgs() << "MCSymbol: " << toString(WS.getType()) << " '" << S << "'"
<< " isDefined=" << S.isDefined() << " isExternal="
<< S.isExternal() << " isTemporary=" << S.isTemporary()
<< " isWeak=" << WS.isWeak() << " isHidden=" << WS.isHidden()
<< " isVariable=" << WS.isVariable() << "\n");
if (WS.isVariable())
continue;
if (WS.isComdat() && !WS.isDefined())
continue;
if (WS.isFunction()) {
unsigned Index;
if (WS.isDefined()) {
if (WS.getOffset() != 0)
report_fatal_error(
"function sections must contain one function each");
if (WS.getSize() == nullptr)
report_fatal_error(
"function symbols must have a size set with .size");
// A definition. Write out the function body.
Index = NumFunctionImports + Functions.size();
WasmFunction Func;
Func.SigIndex = getFunctionType(WS);
Func.Sym = &WS;
WasmIndices[&WS] = Index;
Functions.push_back(Func);
auto &Section = static_cast<MCSectionWasm &>(WS.getSection());
if (const MCSymbolWasm *C = Section.getGroup()) {
Comdats[C->getName()].emplace_back(
WasmComdatEntry{wasm::WASM_COMDAT_FUNCTION, Index});
}
} else {
// An import; the index was assigned above.
Index = WasmIndices.find(&WS)->second;
}
LLVM_DEBUG(dbgs() << " -> function index: " << Index << "\n");
} else if (WS.isData()) {
if (!isInSymtab(WS))
continue;
if (!WS.isDefined()) {
LLVM_DEBUG(dbgs() << " -> segment index: -1"
<< "\n");
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");
auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
assert(DataSection.isWasmData());
// For each data symbol, export it in the symtab as a reference to the
// corresponding Wasm data segment.
wasm::WasmDataReference Ref = wasm::WasmDataReference{
DataSection.getSegmentIndex(),
static_cast<uint32_t>(Layout.getSymbolOffset(WS)),
static_cast<uint32_t>(Size)};
DataLocations[&WS] = Ref;
LLVM_DEBUG(dbgs() << " -> segment index: " << Ref.Segment << "\n");
} else if (WS.isGlobal()) {
// A "true" Wasm global (currently just __stack_pointer)
if (WS.isDefined())
report_fatal_error("don't yet support defined globals");
// An import; the index was assigned above
LLVM_DEBUG(dbgs() << " -> global index: "
<< WasmIndices.find(&WS)->second << "\n");
} else if (WS.isEvent()) {
// C++ exception symbol (__cpp_exception)
unsigned Index;
if (WS.isDefined()) {
Index = NumEventImports + Events.size();
wasm::WasmEventType Event;
Event.SigIndex = getEventType(WS);
Event.Attribute = wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION;
WasmIndices[&WS] = Index;
Events.push_back(Event);
} else {
// An import; the index was assigned above.
Index = WasmIndices.find(&WS)->second;
}
LLVM_DEBUG(dbgs() << " -> event index: " << WasmIndices.find(&WS)->second
<< "\n");
} else {
assert(WS.isSection());
}
}
// Populate WasmIndices and DataLocations for aliased symbols. 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());
// 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);
LLVM_DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *ResolvedSym
<< "'\n");
if (ResolvedSym->isFunction()) {
assert(WasmIndices.count(ResolvedSym) > 0);
uint32_t WasmIndex = WasmIndices.find(ResolvedSym)->second;
WasmIndices[&WS] = WasmIndex;
LLVM_DEBUG(dbgs() << " -> index:" << WasmIndex << "\n");
} else if (ResolvedSym->isData()) {
assert(DataLocations.count(ResolvedSym) > 0);
const wasm::WasmDataReference &Ref =
DataLocations.find(ResolvedSym)->second;
DataLocations[&WS] = Ref;
LLVM_DEBUG(dbgs() << " -> index:" << Ref.Segment << "\n");
} else {
report_fatal_error("don't yet support global/event aliases");
}
}
// Finally, populate the symbol table itself, in its "natural" order.
for (const MCSymbol &S : Asm.symbols()) {
const auto &WS = static_cast<const MCSymbolWasm &>(S);
if (!isInSymtab(WS)) {
WS.setIndex(InvalidIndex);
continue;
}
LLVM_DEBUG(dbgs() << "adding to symtab: " << WS << "\n");
uint32_t Flags = 0;
if (WS.isWeak())
Flags |= wasm::WASM_SYMBOL_BINDING_WEAK;
if (WS.isHidden())
Flags |= wasm::WASM_SYMBOL_VISIBILITY_HIDDEN;
if (!WS.isExternal() && WS.isDefined())
Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL;
if (WS.isUndefined())
Flags |= wasm::WASM_SYMBOL_UNDEFINED;
if (WS.isExported())
Flags |= wasm::WASM_SYMBOL_EXPORTED;
if (WS.getName() != WS.getImportName())
Flags |= wasm::WASM_SYMBOL_EXPLICIT_NAME;
wasm::WasmSymbolInfo Info;
Info.Name = WS.getName();
Info.Kind = WS.getType();
Info.Flags = Flags;
if (!WS.isData()) {
assert(WasmIndices.count(&WS) > 0);
Info.ElementIndex = WasmIndices.find(&WS)->second;
} else if (WS.isDefined()) {
assert(DataLocations.count(&WS) > 0);
Info.DataRef = DataLocations.find(&WS)->second;
}
WS.setIndex(SymbolInfos.size());
SymbolInfos.emplace_back(Info);
}
{
auto HandleReloc = [&](const WasmRelocationEntry &Rel) {
// Functions referenced by a relocation need to put in the table. This is
// purely to make the object file's provisional values readable, and is
// ignored by the linker, which re-calculates the relocations itself.
if (Rel.Type != wasm::R_WASM_TABLE_INDEX_I32 &&
Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB)
return;
assert(Rel.Symbol->isFunction());
const MCSymbolWasm &WS = *resolveSymbol(*Rel.Symbol);
uint32_t FunctionIndex = WasmIndices.find(&WS)->second;
uint32_t TableIndex = TableElems.size() + InitialTableOffset;
if (TableIndices.try_emplace(&WS, TableIndex).second) {
LLVM_DEBUG(dbgs() << " -> adding " << WS.getName()
<< " to table: " << TableIndex << "\n");
TableElems.push_back(FunctionIndex);
registerFunctionType(WS);
}
};
for (const WasmRelocationEntry &RelEntry : CodeRelocations)
HandleReloc(RelEntry);
for (const WasmRelocationEntry &RelEntry : DataRelocations)
HandleReloc(RelEntry);
}
// Translate .init_array section contents into start functions.
for (const MCSection &S : Asm) {
const auto &WS = static_cast<const MCSectionWasm &>(S);
if (WS.getSectionName().startswith(".fini_array"))
report_fatal_error(".fini_array sections are unsupported");
if (!WS.getSectionName().startswith(".init_array"))
continue;
if (WS.getFragmentList().empty())
continue;
// init_array is expected to contain a single non-empty data fragment
if (WS.getFragmentList().size() != 3)
report_fatal_error("only one .init_array section fragment supported");
auto IT = WS.begin();
const MCFragment &EmptyFrag = *IT;
if (EmptyFrag.getKind() != MCFragment::FT_Data)
report_fatal_error(".init_array section should be aligned");
IT = std::next(IT);
const MCFragment &AlignFrag = *IT;
if (AlignFrag.getKind() != MCFragment::FT_Align)
report_fatal_error(".init_array section should be aligned");
if (cast<MCAlignFragment>(AlignFrag).getAlignment() != (is64Bit() ? 8 : 4))
report_fatal_error(".init_array section should be aligned for pointers");
const MCFragment &Frag = *std::next(IT);
if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
report_fatal_error("only data supported in .init_array section");
uint16_t Priority = UINT16_MAX;
unsigned PrefixLength = strlen(".init_array");
if (WS.getSectionName().size() > PrefixLength) {
if (WS.getSectionName()[PrefixLength] != '.')
report_fatal_error(
".init_array section priority should start with '.'");
if (WS.getSectionName()
.substr(PrefixLength + 1)
.getAsInteger(10, Priority))
report_fatal_error("invalid .init_array section priority");
}
const auto &DataFrag = cast<MCDataFragment>(Frag);
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; ++P) {
if (*P != 0)
report_fatal_error("non-symbolic data in .init_array section");
}
for (const MCFixup &Fixup : DataFrag.getFixups()) {
assert(Fixup.getKind() ==
MCFixup::getKindForSize(is64Bit() ? 8 : 4, false));
const MCExpr *Expr = Fixup.getValue();
auto *SymRef = dyn_cast<MCSymbolRefExpr>(Expr);
if (!SymRef)
report_fatal_error("fixups in .init_array should be symbol references");
const auto &TargetSym = cast<const MCSymbolWasm>(SymRef->getSymbol());
if (TargetSym.getIndex() == InvalidIndex)
report_fatal_error("symbols in .init_array should exist in symbtab");
if (!TargetSym.isFunction())
report_fatal_error("symbols in .init_array should be for functions");
InitFuncs.push_back(
std::make_pair(Priority, TargetSym.getIndex()));
}
}
// Write out the Wasm header.
writeHeader(Asm);
writeTypeSection(Signatures);
writeImportSection(Imports, DataSize, TableElems.size());
writeFunctionSection(Functions);
// Skip the "table" section; we import the table instead.
// Skip the "memory" section; we import the memory instead.
writeGlobalSection();
writeEventSection(Events);
writeExportSection(Exports);
writeElemSection(TableElems);
writeCodeSection(Asm, Layout, Functions);
writeDataSection();
for (auto &CustomSection : CustomSections)
writeCustomSection(CustomSection, Asm, Layout);
writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats);
writeRelocSection(CodeSectionIndex, "CODE", CodeRelocations);
writeRelocSection(DataSectionIndex, "DATA", DataRelocations);
writeCustomRelocSections();
if (ProducersSection)
writeCustomSection(*ProducersSection, Asm, Layout);
if (TargetFeaturesSection)
writeCustomSection(*TargetFeaturesSection, Asm, Layout);
// TODO: Translate the .comment section to the output.
return W.OS.tell() - StartOffset;
}
std::unique_ptr<MCObjectWriter>
llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
raw_pwrite_stream &OS) {
return llvm::make_unique<WasmObjectWriter>(std::move(MOTW), OS);
}
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