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llvm-mirror/lib/MC/WasmObjectWriter.cpp
Wouter van Oortmerssen 59520b4419 [WebAssembly] Prevent data inside text sections in assembly 
This is not supported in Wasm, unless the data was encoded instructions, but that wouldn't work with the assembler's other functionality (enforcing nesting etc.).

Fixes: https://bugs.llvm.org/show_bug.cgi?id=48971

Differential Revision: https://reviews.llvm.org/D95838
2021-02-05 13:48:25 -08:00

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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/BinaryFormat/WasmTraits.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/EndianStream.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 {
// When we create the indirect function table we start at 1, so that there is
// and empty 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;
};
// 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;
uint64_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 { return wasm::relocTypeHasAddend(Type); }
void print(raw_ostream &Out) const {
Out << wasm::relocTypetoString(Type) << " Off=" << Offset
<< ", Sym=" << *Symbol << ", Addend=" << Addend
<< ", FixupSection=" << FixupSection->getName();
}
#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.
template <int W>
void writePatchableLEB(raw_pwrite_stream &Stream, uint64_t X, uint64_t Offset) {
uint8_t Buffer[W];
unsigned SizeLen = encodeULEB128(X, Buffer, W);
assert(SizeLen == W);
Stream.pwrite((char *)Buffer, SizeLen, Offset);
}
// Write X as an signed LEB value at offset Offset in Stream, padded
// to allow patching.
template <int W>
void writePatchableSLEB(raw_pwrite_stream &Stream, int64_t X, uint64_t Offset) {
uint8_t Buffer[W];
unsigned SizeLen = encodeSLEB128(X, Buffer, W);
assert(SizeLen == W);
Stream.pwrite((char *)Buffer, SizeLen, Offset);
}
// Write X as a plain integer value at offset Offset in Stream.
static void patchI32(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 void patchI64(raw_pwrite_stream &Stream, uint64_t X, uint64_t Offset) {
uint8_t Buffer[8];
support::endian::write64le(Buffer, X);
Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
}
bool isDwoSection(const MCSection &Sec) {
return Sec.getName().endswith(".dwo");
}
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;
// 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> TableIndices;
// Maps function/global/table symbols to the
// function/global/table/event/section index space.
DenseMap<const MCSymbolWasm *, uint32_t> WasmIndices;
DenseMap<const MCSymbolWasm *, uint32_t> GOTIndices;
// 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<wasm::WasmSignature, uint32_t> SignatureIndices;
SmallVector<wasm::WasmSignature, 4> Signatures;
SmallVector<WasmDataSegment, 4> DataSegments;
unsigned NumFunctionImports = 0;
unsigned NumGlobalImports = 0;
unsigned NumTableImports = 0;
unsigned NumEventImports = 0;
uint32_t SectionCount = 0;
enum class DwoMode {
AllSections,
NonDwoOnly,
DwoOnly,
};
bool IsSplitDwarf = false;
raw_pwrite_stream *OS = nullptr;
raw_pwrite_stream *DwoOS = nullptr;
// TargetObjectWriter wranppers.
bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
bool isEmscripten() const { return TargetObjectWriter->isEmscripten(); }
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_)
: TargetObjectWriter(std::move(MOTW)), OS(&OS_) {}
WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
raw_pwrite_stream &OS_, raw_pwrite_stream &DwoOS_)
: TargetObjectWriter(std::move(MOTW)), IsSplitDwarf(true), OS(&OS_),
DwoOS(&DwoOS_) {}
private:
void reset() override {
CodeRelocations.clear();
DataRelocations.clear();
TypeIndices.clear();
WasmIndices.clear();
GOTIndices.clear();
TableIndices.clear();
DataLocations.clear();
CustomSections.clear();
ProducersSection.reset();
TargetFeaturesSection.reset();
CustomSectionsRelocations.clear();
SignatureIndices.clear();
Signatures.clear();
DataSegments.clear();
SectionFunctions.clear();
NumFunctionImports = 0;
NumGlobalImports = 0;
NumTableImports = 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;
void prepareImports(SmallVectorImpl<wasm::WasmImport> &Imports,
MCAssembler &Asm, const MCAsmLayout &Layout);
uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
uint64_t writeOneObject(MCAssembler &Asm, const MCAsmLayout &Layout,
DwoMode Mode);
void writeString(const StringRef Str) {
encodeULEB128(Str.size(), W->OS);
W->OS << Str;
}
void writeI32(int32_t val) {
char Buffer[4];
support::endian::write32le(Buffer, val);
W->OS.write(Buffer, sizeof(Buffer));
}
void writeI64(int64_t val) {
char Buffer[8];
support::endian::write64le(Buffer, val);
W->OS.write(Buffer, sizeof(Buffer));
}
void writeValueType(wasm::ValType Ty) { W->OS << static_cast<char>(Ty); }
void writeTypeSection(ArrayRef<wasm::WasmSignature> Signatures);
void writeImportSection(ArrayRef<wasm::WasmImport> Imports, uint64_t DataSize,
uint32_t NumElements);
void writeFunctionSection(ArrayRef<WasmFunction> Functions);
void writeExportSection(ArrayRef<wasm::WasmExport> Exports);
void writeElemSection(ArrayRef<uint32_t> TableElems);
void writeDataCountSection();
uint32_t writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
ArrayRef<WasmFunction> Functions);
uint32_t writeDataSection(const MCAsmLayout &Layout);
void writeEventSection(ArrayRef<wasm::WasmEventType> Events);
void writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals);
void writeTableSection(ArrayRef<wasm::WasmTable> Tables);
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();
uint64_t getProvisionalValue(const WasmRelocationEntry &RelEntry,
const MCAsmLayout &Layout);
void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
uint64_t ContentsOffset, const MCAsmLayout &Layout);
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<5>(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) {
// As a stopgap measure until call_indirect instructions start explicitly
// referencing the indirect function table via TABLE_NUMBER relocs, ensure
// that the indirect function table import makes it to the output if anything
// in the compilation unit has caused it to be present.
if (auto *Sym = Asm.getContext().lookupSymbol("__indirect_function_table"))
Asm.registerSymbol(*Sym);
// 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.getName());
}
}
}
void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
// The WebAssembly backend should never generate FKF_IsPCRel fixups
assert(!(Asm.getBackend().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()) {
// To get here the A - B expression must have failed evaluateAsRelocatable.
// This means either A or B must be undefined and in WebAssembly we can't
// support either of those cases.
const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol());
Ctx.reportError(
Fixup.getLoc(),
Twine("symbol '") + SymB.getName() +
"': unsupported subtraction expression used in relocation.");
return;
}
// We either rejected the fixup or folded B into C at this point.
const MCSymbolRefExpr *RefA = Target.getSymA();
const auto *SymA = cast<MCSymbolWasm>(&RefA->getSymbol());
// The .init_array isn't translated as data, so don't do relocations in it.
if (FixupSection.getName().startswith(".init_array")) {
SymA->setUsedInInitArray();
return;
}
if (SymA->isVariable()) {
const MCExpr *Expr = SymA->getVariableValue();
if (const auto *Inner = dyn_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 = TargetObjectWriter->getRelocType(Target, Fixup);
// 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_FUNCTION_OFFSET_I64 ||
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()) {
auto SecSymIt = SectionFunctions.find(&SecA);
if (SecSymIt == SectionFunctions.end())
report_fatal_error("section doesn\'t have defining symbol");
SectionSymbol = SecSymIt->second;
} else {
SectionSymbol = SecA.getBeginSymbol();
}
if (!SectionSymbol)
report_fatal_error("section symbol is required for relocation");
C += Layout.getSymbolOffset(*SymA);
SymA = cast<MCSymbolWasm>(SectionSymbol);
}
if (Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB ||
Type == wasm::R_WASM_TABLE_INDEX_SLEB ||
Type == wasm::R_WASM_TABLE_INDEX_SLEB64 ||
Type == wasm::R_WASM_TABLE_INDEX_I32 ||
Type == wasm::R_WASM_TABLE_INDEX_I64) {
// TABLE_INDEX relocs implicitly use the default indirect function table.
auto TableName = "__indirect_function_table";
MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(TableName));
if (Sym) {
if (!Sym->isFunctionTable())
Ctx.reportError(
Fixup.getLoc(),
"symbol '__indirect_function_table' is not a function table");
} else {
Sym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(TableName));
Sym->setFunctionTable();
// The default function table is synthesized by the linker.
Sym->setUndefined();
}
Sym->setUsedInReloc();
Asm.registerSymbol(*Sym);
}
// 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();
}
if (RefA->getKind() == MCSymbolRefExpr::VK_GOT)
SymA->setUsedInGOT();
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");
}
}
// 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.
uint64_t
WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry,
const MCAsmLayout &Layout) {
if ((RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_LEB ||
RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_I32) &&
!RelEntry.Symbol->isGlobal()) {
assert(GOTIndices.count(RelEntry.Symbol) > 0 && "symbol not found in GOT index space");
return GOTIndices[RelEntry.Symbol];
}
switch (RelEntry.Type) {
case wasm::R_WASM_TABLE_INDEX_REL_SLEB:
case wasm::R_WASM_TABLE_INDEX_SLEB:
case wasm::R_WASM_TABLE_INDEX_SLEB64:
case wasm::R_WASM_TABLE_INDEX_I32:
case wasm::R_WASM_TABLE_INDEX_I64: {
// Provisional value is table address of the resolved symbol itself
const MCSymbolWasm *Base =
cast<MCSymbolWasm>(Layout.getBaseSymbol(*RelEntry.Symbol));
assert(Base->isFunction());
if (RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB)
return TableIndices[Base] - InitialTableOffset;
else
return TableIndices[Base];
}
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_GLOBAL_INDEX_I32:
case wasm::R_WASM_EVENT_INDEX_LEB:
case wasm::R_WASM_TABLE_NUMBER_LEB:
// Provisional value is function/global/event Wasm index
assert(WasmIndices.count(RelEntry.Symbol) > 0 && "symbol not found in wasm index space");
return WasmIndices[RelEntry.Symbol];
case wasm::R_WASM_FUNCTION_OFFSET_I32:
case wasm::R_WASM_FUNCTION_OFFSET_I64:
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_LEB64:
case wasm::R_WASM_MEMORY_ADDR_SLEB:
case wasm::R_WASM_MEMORY_ADDR_SLEB64:
case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64:
case wasm::R_WASM_MEMORY_ADDR_I32:
case wasm::R_WASM_MEMORY_ADDR_I64:
case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB: {
// Provisional value is address of the global plus the offset
const MCSymbolWasm *Base =
cast<MCSymbolWasm>(Layout.getBaseSymbol(*RelEntry.Symbol));
// For undefined symbols, use zero
if (!Base->isDefined())
return 0;
const wasm::WasmDataReference &BaseRef = DataLocations[Base],
&SymRef = DataLocations[RelEntry.Symbol];
const WasmDataSegment &Segment = DataSegments[BaseRef.Segment];
// Ignore overflow. LLVM allows address arithmetic to silently wrap.
return Segment.Offset + BaseRef.Offset + SymRef.Offset + RelEntry.Addend;
}
default:
llvm_unreachable("invalid relocation type");
}
}
static void addData(SmallVectorImpl<char> &DataBytes,
MCSectionWasm &DataSection) {
LLVM_DEBUG(errs() << "addData: " << DataSection.getName() << "\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();
llvm::append_range(DataBytes, Contents);
} else {
const auto &DataFrag = cast<MCDataFragment>(Frag);
const SmallVectorImpl<char> &Contents = DataFrag.getContents();
llvm::append_range(DataBytes, Contents);
}
}
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,
const MCAsmLayout &Layout) {
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");
auto Value = getProvisionalValue(RelEntry, Layout);
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:
case wasm::R_WASM_TABLE_NUMBER_LEB:
writePatchableLEB<5>(Stream, Value, Offset);
break;
case wasm::R_WASM_MEMORY_ADDR_LEB64:
writePatchableLEB<10>(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:
case wasm::R_WASM_GLOBAL_INDEX_I32:
patchI32(Stream, Value, Offset);
break;
case wasm::R_WASM_TABLE_INDEX_I64:
case wasm::R_WASM_MEMORY_ADDR_I64:
case wasm::R_WASM_FUNCTION_OFFSET_I64:
patchI64(Stream, Value, Offset);
break;
case wasm::R_WASM_TABLE_INDEX_SLEB:
case wasm::R_WASM_TABLE_INDEX_REL_SLEB:
case wasm::R_WASM_MEMORY_ADDR_SLEB:
case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB:
writePatchableSLEB<5>(Stream, Value, Offset);
break;
case wasm::R_WASM_TABLE_INDEX_SLEB64:
case wasm::R_WASM_MEMORY_ADDR_SLEB64:
case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64:
writePatchableSLEB<10>(Stream, Value, Offset);
break;
default:
llvm_unreachable("invalid relocation type");
}
}
}
void WasmObjectWriter::writeTypeSection(
ArrayRef<wasm::WasmSignature> Signatures) {
if (Signatures.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_TYPE);
encodeULEB128(Signatures.size(), W->OS);
for (const wasm::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,
uint64_t DataSize,
uint32_t NumElements) {
if (Imports.empty())
return;
uint64_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(Import.Memory.Flags, W->OS);
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::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::writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals) {
if (Globals.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_GLOBAL);
encodeULEB128(Globals.size(), W->OS);
for (const wasm::WasmGlobal &Global : Globals) {
encodeULEB128(Global.Type.Type, W->OS);
W->OS << char(Global.Type.Mutable);
W->OS << char(Global.InitExpr.Opcode);
switch (Global.Type.Type) {
case wasm::WASM_TYPE_I32:
encodeSLEB128(0, W->OS);
break;
case wasm::WASM_TYPE_I64:
encodeSLEB128(0, W->OS);
break;
case wasm::WASM_TYPE_F32:
writeI32(0);
break;
case wasm::WASM_TYPE_F64:
writeI64(0);
break;
case wasm::WASM_TYPE_EXTERNREF:
writeValueType(wasm::ValType::EXTERNREF);
break;
default:
llvm_unreachable("unexpected type");
}
W->OS << char(wasm::WASM_OPCODE_END);
}
endSection(Section);
}
void WasmObjectWriter::writeTableSection(ArrayRef<wasm::WasmTable> Tables) {
if (Tables.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_TABLE);
encodeULEB128(Tables.size(), W->OS);
for (const wasm::WasmTable &Table : Tables) {
encodeULEB128(Table.Type.ElemType, W->OS);
encodeULEB128(Table.Type.Limits.Flags, W->OS);
encodeULEB128(Table.Type.Limits.Initial, W->OS);
if (Table.Type.Limits.Flags & wasm::WASM_LIMITS_FLAG_HAS_MAX)
encodeULEB128(Table.Type.Limits.Maximum, 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::writeDataCountSection() {
if (DataSegments.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_DATACOUNT);
encodeULEB128(DataSegments.size(), W->OS);
endSection(Section);
}
uint32_t WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
const MCAsmLayout &Layout,
ArrayRef<WasmFunction> Functions) {
if (Functions.empty())
return 0;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_CODE);
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, Layout);
endSection(Section);
return Section.Index;
}
uint32_t WasmObjectWriter::writeDataSection(const MCAsmLayout &Layout) {
if (DataSegments.empty())
return 0;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_DATA);
encodeULEB128(DataSegments.size(), W->OS); // count
for (const WasmDataSegment &Segment : DataSegments) {
encodeULEB128(Segment.InitFlags, W->OS); // flags
if (Segment.InitFlags & wasm::WASM_DATA_SEGMENT_HAS_MEMINDEX)
encodeULEB128(0, W->OS); // memory index
if ((Segment.InitFlags & wasm::WASM_DATA_SEGMENT_IS_PASSIVE) == 0) {
W->OS << char(is64Bit() ? wasm::WASM_OPCODE_I64_CONST
: 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, Layout);
endSection(Section);
return Section.Index;
}
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.
llvm::stable_sort(
Relocs, [](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:
case wasm::WASM_SYMBOL_TYPE_TABLE:
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, Layout);
}
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());
wasm::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() << "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.
wasm::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() || Sym.isUsedInInitArray())
return true;
if (Sym.isComdat() && !Sym.isDefined())
return false;
if (Sym.isTemporary())
return false;
if (Sym.isSection())
return false;
return true;
}
void WasmObjectWriter::prepareImports(
SmallVectorImpl<wasm::WasmImport> &Imports, MCAssembler &Asm,
const MCAsmLayout &Layout) {
// 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;
MemImport.Memory.Flags = is64Bit() ? wasm::WASM_LIMITS_FLAG_IS_64
: wasm::WASM_LIMITS_FLAG_NONE;
Imports.push_back(MemImport);
// 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()) {
const auto *BS = Layout.getBaseSymbol(S);
if (!BS)
report_fatal_error(Twine(S.getName()) +
": absolute addressing not supported!");
registerFunctionType(*cast<MCSymbolWasm>(BS));
}
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);
assert(WasmIndices.count(&WS) == 0);
WasmIndices[&WS] = NumFunctionImports++;
} else if (WS.isGlobal()) {
if (WS.isWeak())
report_fatal_error("undefined global symbol cannot be weak");
wasm::WasmImport Import;
Import.Field = WS.getImportName();
Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
Import.Module = WS.getImportModule();
Import.Global = WS.getGlobalType();
Imports.push_back(Import);
assert(WasmIndices.count(&WS) == 0);
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);
assert(WasmIndices.count(&WS) == 0);
WasmIndices[&WS] = NumEventImports++;
} else if (WS.isTable()) {
if (WS.isWeak())
report_fatal_error("undefined table symbol cannot be weak");
wasm::WasmImport Import;
Import.Module = WS.getImportModule();
Import.Field = WS.getImportName();
Import.Kind = wasm::WASM_EXTERNAL_TABLE;
wasm::ValType ElemType = WS.getTableType();
Import.Table.ElemType = uint8_t(ElemType);
// FIXME: Extend table type to include limits? For now we don't specify
// a min or max which does not place any restrictions on the size of the
// imported table.
Import.Table.Limits = {wasm::WASM_LIMITS_FLAG_NONE, 0, 0};
Imports.push_back(Import);
assert(WasmIndices.count(&WS) == 0);
WasmIndices[&WS] = NumTableImports++;
}
}
}
// Add imports for GOT globals
for (const MCSymbol &S : Asm.symbols()) {
const auto &WS = static_cast<const MCSymbolWasm &>(S);
if (WS.isUsedInGOT()) {
wasm::WasmImport Import;
if (WS.isFunction())
Import.Module = "GOT.func";
else
Import.Module = "GOT.mem";
Import.Field = WS.getName();
Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
Import.Global = {wasm::WASM_TYPE_I32, true};
Imports.push_back(Import);
assert(GOTIndices.count(&WS) == 0);
GOTIndices[&WS] = NumGlobalImports++;
}
}
}
uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
support::endian::Writer MainWriter(*OS, support::little);
W = &MainWriter;
if (IsSplitDwarf) {
uint64_t TotalSize = writeOneObject(Asm, Layout, DwoMode::NonDwoOnly);
assert(DwoOS);
support::endian::Writer DwoWriter(*DwoOS, support::little);
W = &DwoWriter;
return TotalSize + writeOneObject(Asm, Layout, DwoMode::DwoOnly);
} else {
return writeOneObject(Asm, Layout, DwoMode::AllSections);
}
}
uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
const MCAsmLayout &Layout,
DwoMode Mode) {
uint64_t StartOffset = W->OS.tell();
SectionCount = 0;
CustomSections.clear();
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::WasmGlobal, 1> Globals;
SmallVector<wasm::WasmTable, 1> Tables;
SmallVector<wasm::WasmSymbolInfo, 4> SymbolInfos;
SmallVector<std::pair<uint16_t, uint32_t>, 2> InitFuncs;
std::map<StringRef, std::vector<WasmComdatEntry>> Comdats;
uint64_t DataSize = 0;
if (Mode != DwoMode::DwoOnly) {
prepareImports(Imports, Asm, Layout);
}
// Populate DataSegments and CustomSections, which must be done before
// populating DataLocations.
for (MCSection &Sec : Asm) {
auto &Section = static_cast<MCSectionWasm &>(Sec);
StringRef SectionName = Section.getName();
if (Mode == DwoMode::NonDwoOnly && isDwoSection(Sec))
continue;
if (Mode == DwoMode::DwoOnly && !isDwoSection(Sec))
continue;
LLVM_DEBUG(dbgs() << "Processing Section " << SectionName << " group "
<< Section.getGroup() << "\n";);
// .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_DATA_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) {
assert(WasmIndices.count(cast<MCSymbolWasm>(Begin)) == 0);
WasmIndices[cast<MCSymbolWasm>(Begin)] = CustomSections.size();
}
// Separate out the producers and target features sections
if (Name == "producers") {
ProducersSection = std::make_unique<WasmCustomSection>(Name, &Section);
continue;
}
if (Name == "target_features") {
TargetFeaturesSection =
std::make_unique<WasmCustomSection>(Name, &Section);
continue;
}
// Custom sections can also belong to COMDAT groups. In this case the
// decriptor's "index" field is the section index (in the final object
// file), but that is not known until after layout, so it must be fixed up
// later
if (const MCSymbolWasm *C = Section.getGroup()) {
Comdats[C->getName()].emplace_back(
WasmComdatEntry{wasm::WASM_COMDAT_SECTION,
static_cast<uint32_t>(CustomSections.size())});
}
CustomSections.emplace_back(Name, &Section);
}
}
if (Mode != DwoMode::DwoOnly) {
// 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().getValueOr(wasm::WASM_SYMBOL_TYPE_DATA))
<< " '" << 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;
assert(WasmIndices.count(&WS) == 0);
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});
}
if (WS.hasExportName()) {
wasm::WasmExport Export;
Export.Name = WS.getExportName();
Export.Kind = wasm::WASM_EXTERNAL_FUNCTION;
Export.Index = Index;
Exports.push_back(Export);
}
} 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());
if (!DataSection.isWasmData())
report_fatal_error("data symbols must live in a data section: " +
WS.getName());
// 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(), Layout.getSymbolOffset(WS),
static_cast<uint64_t>(Size)};
assert(DataLocations.count(&WS) == 0);
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()) {
wasm::WasmGlobal Global;
Global.Type = WS.getGlobalType();
Global.Index = NumGlobalImports + Globals.size();
switch (Global.Type.Type) {
case wasm::WASM_TYPE_I32:
Global.InitExpr.Opcode = wasm::WASM_OPCODE_I32_CONST;
break;
case wasm::WASM_TYPE_I64:
Global.InitExpr.Opcode = wasm::WASM_OPCODE_I64_CONST;
break;
case wasm::WASM_TYPE_F32:
Global.InitExpr.Opcode = wasm::WASM_OPCODE_F32_CONST;
break;
case wasm::WASM_TYPE_F64:
Global.InitExpr.Opcode = wasm::WASM_OPCODE_F64_CONST;
break;
case wasm::WASM_TYPE_EXTERNREF:
Global.InitExpr.Opcode = wasm::WASM_OPCODE_REF_NULL;
break;
default:
llvm_unreachable("unexpected type");
}
assert(WasmIndices.count(&WS) == 0);
WasmIndices[&WS] = Global.Index;
Globals.push_back(Global);
} else {
// An import; the index was assigned above
LLVM_DEBUG(dbgs() << " -> global index: "
<< WasmIndices.find(&WS)->second << "\n");
}
} else if (WS.isTable()) {
if (WS.isDefined()) {
wasm::WasmTable Table;
Table.Index = NumTableImports + Tables.size();
Table.Type.ElemType = static_cast<uint8_t>(WS.getTableType());
// FIXME: Work on custom limits is ongoing
Table.Type.Limits = {wasm::WASM_LIMITS_FLAG_NONE, 0, 0};
assert(WasmIndices.count(&WS) == 0);
WasmIndices[&WS] = Table.Index;
Tables.push_back(Table);
}
LLVM_DEBUG(dbgs() << " -> table 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;
assert(WasmIndices.count(&WS) == 0);
WasmIndices[&WS] = Index;
Events.push_back(Event);
} else {
// An import; the index was assigned above.
assert(WasmIndices.count(&WS) > 0);
}
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());
const auto *BS = Layout.getBaseSymbol(S);
if (!BS)
report_fatal_error(Twine(S.getName()) +
": absolute addressing not supported!");
const MCSymbolWasm *Base = cast<MCSymbolWasm>(BS);
// Find the target symbol of this weak alias and export that index
const auto &WS = static_cast<const MCSymbolWasm &>(S);
LLVM_DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *Base
<< "'\n");
if (Base->isFunction()) {
assert(WasmIndices.count(Base) > 0);
uint32_t WasmIndex = WasmIndices.find(Base)->second;
assert(WasmIndices.count(&WS) == 0);
WasmIndices[&WS] = WasmIndex;
LLVM_DEBUG(dbgs() << " -> index:" << WasmIndex << "\n");
} else if (Base->isData()) {
auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
uint64_t Offset = Layout.getSymbolOffset(S);
int64_t Size = 0;
// For data symbol alias we use the size of the base symbol as the
// size of the alias. When an offset from the base is involved this
// can result in a offset + size goes past the end of the data section
// which out object format doesn't support. So we must clamp it.
if (!Base->getSize()->evaluateAsAbsolute(Size, Layout))
report_fatal_error(".size expression must be evaluatable");
const WasmDataSegment &Segment =
DataSegments[DataSection.getSegmentIndex()];
Size =
std::min(static_cast<uint64_t>(Size), Segment.Data.size() - Offset);
wasm::WasmDataReference Ref = wasm::WasmDataReference{
DataSection.getSegmentIndex(),
static_cast<uint32_t>(Layout.getSymbolOffset(S)),
static_cast<uint32_t>(Size)};
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;
}
if (WS.isTable() && WS.getName() == "__indirect_function_table") {
// For the moment, don't emit table symbols -- wasm-ld can't handle them.
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.isNoStrip()) {
Flags |= wasm::WASM_SYMBOL_NO_STRIP;
if (isEmscripten()) {
Flags |= wasm::WASM_SYMBOL_EXPORTED;
}
}
if (WS.hasImportName())
Flags |= wasm::WASM_SYMBOL_EXPLICIT_NAME;
if (WS.hasExportName())
Flags |= wasm::WASM_SYMBOL_EXPORTED;
wasm::WasmSymbolInfo Info;
Info.Name = WS.getName();
Info.Kind = WS.getType().getValueOr(wasm::WASM_SYMBOL_TYPE_DATA);
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_I64 &&
Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB &&
Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB64 &&
Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB)
return;
assert(Rel.Symbol->isFunction());
const MCSymbolWasm *Base =
cast<MCSymbolWasm>(Layout.getBaseSymbol(*Rel.Symbol));
uint32_t FunctionIndex = WasmIndices.find(Base)->second;
uint32_t TableIndex = TableElems.size() + InitialTableOffset;
if (TableIndices.try_emplace(Base, TableIndex).second) {
LLVM_DEBUG(dbgs() << " -> adding " << Base->getName()
<< " to table: " << TableIndex << "\n");
TableElems.push_back(FunctionIndex);
registerFunctionType(*Base);
}
};
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.getName().startswith(".fini_array"))
report_fatal_error(".fini_array sections are unsupported");
if (!WS.getName().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.getName().size() > PrefixLength) {
if (WS.getName()[PrefixLength] != '.')
report_fatal_error(
".init_array section priority should start with '.'");
if (WS.getName().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 symtab");
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);
uint32_t CodeSectionIndex, DataSectionIndex;
if (Mode != DwoMode::DwoOnly) {
writeTypeSection(Signatures);
writeImportSection(Imports, DataSize, TableElems.size());
writeFunctionSection(Functions);
writeTableSection(Tables);
// Skip the "memory" section; we import the memory instead.
writeEventSection(Events);
writeGlobalSection(Globals);
writeExportSection(Exports);
writeElemSection(TableElems);
writeDataCountSection();
CodeSectionIndex = writeCodeSection(Asm, Layout, Functions);
DataSectionIndex = writeDataSection(Layout);
}
// The Sections in the COMDAT list have placeholder indices (their index among
// custom sections, rather than among all sections). Fix them up here.
for (auto &Group : Comdats) {
for (auto &Entry : Group.second) {
if (Entry.Kind == wasm::WASM_COMDAT_SECTION) {
Entry.Index += SectionCount;
}
}
}
for (auto &CustomSection : CustomSections)
writeCustomSection(CustomSection, Asm, Layout);
if (Mode != DwoMode::DwoOnly) {
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 std::make_unique<WasmObjectWriter>(std::move(MOTW), OS);
}
std::unique_ptr<MCObjectWriter>
llvm::createWasmDwoObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
raw_pwrite_stream &OS,
raw_pwrite_stream &DwoOS) {
return std::make_unique<WasmObjectWriter>(std::move(MOTW), OS, DwoOS);
}
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