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WasmObjectWriter.cpp
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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 LinkingFlags;
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/tag/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 NumTagImports = 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 writeStringWithAlignment(const StringRef Str, unsigned Alignment);
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(const MCSymbolWasm *IndirectFunctionTable,
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 writeTagSection(ArrayRef<uint32_t> TagTypes);
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 getTagType(const MCSymbolWasm &Symbol);
void registerFunctionType(const MCSymbolWasm &Symbol);
void registerTagType(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++;
}
// Write a string with extra paddings for trailing alignment
// TODO: support alignment at asm and llvm level?
void WasmObjectWriter::writeStringWithAlignment(const StringRef Str,
unsigned Alignment) {
// Calculate the encoded size of str length and add pads based on it and
// alignment.
raw_null_ostream NullOS;
uint64_t StrSizeLength = encodeULEB128(Str.size(), NullOS);
uint64_t Offset = W->OS.tell() + StrSizeLength + Str.size();
uint64_t Paddings = offsetToAlignment(Offset, Align(Alignment));
Offset += Paddings;
// LEB128 greater than 5 bytes is invalid
assert((StrSizeLength + Paddings) <= 5 && "too long string to align");
encodeSLEB128(Str.size(), W->OS, StrSizeLength + Paddings);
W->OS << Str;
assert(W->OS.tell() == Offset && "invalid padding");
}
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.
if (Name != "__clangast") {
writeString(Name);
} else {
// The on-disk hashtable in clangast needs to be aligned by 4 bytes.
writeStringWithAlignment(Name, 4);
}
// 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) {
// Some compilation units require the indirect function table to be present
// but don't explicitly reference it. This is the case for call_indirect
// without the reference-types feature, and also function bitcasts in all
// cases. In those cases the __indirect_function_table has the
// WASM_SYMBOL_NO_STRIP attribute. Here we make sure this symbol makes it to
// the assembler, if needed.
if (auto *Sym = Asm.getContext().lookupSymbol("__indirect_function_table")) {
const auto *WasmSym = static_cast<const MCSymbolWasm *>(Sym);
if (WasmSym->isNoStrip())
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();
bool IsLocRel = false;
if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol());
if (FixupSection.getKind().isText()) {
Ctx.reportError(Fixup.getLoc(),
Twine("symbol '") + SymB.getName() +
"' unsupported subtraction expression used in "
"relocation in code section.");
return;
}
if (SymB.isUndefined()) {
Ctx.reportError(Fixup.getLoc(),
Twine("symbol '") + SymB.getName() +
"' can not be undefined in a subtraction expression");
return;
}
const MCSection &SecB = SymB.getSection();
if (&SecB != &FixupSection) {
Ctx.reportError(Fixup.getLoc(),
Twine("symbol '") + SymB.getName() +
"' can not be placed in a different section");
return;
}
IsLocRel = true;
C += FixupOffset - Layout.getSymbolOffset(SymB);
}
// 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, FixupSection, IsLocRel);
// 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) &&
SymA->isDefined()) {
// SymA can be a temp data symbol that represents a function (in which case
// it needs to be replaced by the section symbol), [XXX and it apparently
// later gets changed again to a func symbol?] or it can be a real
// function symbol, in which case it can be left as-is.
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_REL_SLEB64 ||
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.
// We require the function table to have already been defined.
auto TableName = "__indirect_function_table";
MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(TableName));
if (!Sym) {
report_fatal_error("missing indirect function table symbol");
} else {
if (!Sym->isFunctionTable())
report_fatal_error("__indirect_function_table symbol has wrong type");
// Ensure that __indirect_function_table reaches the output.
Sym->setNoStrip();
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();
}
switch (RefA->getKind()) {
case MCSymbolRefExpr::VK_GOT:
case MCSymbolRefExpr::VK_WASM_GOT_TLS:
SymA->setUsedInGOT();
break;
default:
break;
}
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_REL_SLEB64:
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 ||
RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB64)
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_TAG_INDEX_LEB:
case wasm::R_WASM_TABLE_NUMBER_LEB:
// Provisional value is function/global/tag 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: {
if (!RelEntry.Symbol->isDefined())
return 0;
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:
case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64:
case wasm::R_WASM_MEMORY_ADDR_LOCREL_I32: {
// Provisional value is address of the global plus the offset
// For undefined symbols, use zero
if (!RelEntry.Symbol->isDefined())
return 0;
const wasm::WasmDataReference &SymRef = DataLocations[RelEntry.Symbol];
const WasmDataSegment &Segment = DataSegments[SymRef.Segment];
// Ignore overflow. LLVM allows address arithmetic to silently wrap.
return Segment.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_TAG_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:
case wasm::R_WASM_MEMORY_ADDR_LOCREL_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_TABLE_INDEX_REL_SLEB64:
case wasm::R_WASM_MEMORY_ADDR_SLEB64:
case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64:
case wasm::R_WASM_MEMORY_ADDR_TLS_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_TAG:
W->OS << char(0); // Reserved 'attribute' field
encodeULEB128(Import.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::writeTagSection(ArrayRef<uint32_t> TagTypes) {
if (TagTypes.empty())
return;
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_TAG);
encodeULEB128(TagTypes.size(), W->OS);
for (uint32_t Index : TagTypes) {
W->OS << char(0); // Reserved 'attribute' field
encodeULEB128(Index, 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.Minimum, 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(
const MCSymbolWasm *IndirectFunctionTable, ArrayRef<uint32_t> TableElems) {
if (TableElems.empty())
return;
assert(IndirectFunctionTable);
SectionBookkeeping Section;
startSection(Section, wasm::WASM_SEC_ELEM);
encodeULEB128(1, W->OS); // number of "segments"
assert(WasmIndices.count(IndirectFunctionTable));
uint32_t TableNumber = WasmIndices.find(IndirectFunctionTable)->second;
uint32_t Flags = 0;
if (TableNumber)
Flags |= wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER;
encodeULEB128(Flags, W->OS);
if (Flags & wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER)
encodeULEB128(TableNumber, W->OS); // the table number
// init expr for starting offset
W->OS << char(wasm::WASM_OPCODE_I32_CONST);
encodeSLEB128(InitialTableOffset, W->OS);
W->OS << char(wasm::WASM_OPCODE_END);