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Writer.cpp
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Writer.cpp
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//===- Writer.cpp ---------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "Writer.h"
#include "Config.h"
#include "InputChunks.h"
#include "InputGlobal.h"
#include "OutputSections.h"
#include "OutputSegment.h"
#include "SymbolTable.h"
#include "WriterUtils.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "lld/Common/Strings.h"
#include "lld/Common/Threads.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/BinaryFormat/Wasm.h"
#include "llvm/Support/FileOutputBuffer.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/LEB128.h"
#include <cstdarg>
#include <map>
#define DEBUG_TYPE "lld"
using namespace llvm;
using namespace llvm::wasm;
using namespace lld;
using namespace lld::wasm;
static constexpr int kStackAlignment = 16;
static constexpr int kInitialTableOffset = 1;
namespace {
// Traits for using WasmSignature in a DenseMap.
struct WasmSignatureDenseMapInfo {
static WasmSignature getEmptyKey() {
WasmSignature Sig;
Sig.ReturnType = 1;
return Sig;
}
static WasmSignature getTombstoneKey() {
WasmSignature Sig;
Sig.ReturnType = 2;
return Sig;
}
static unsigned getHashValue(const WasmSignature &Sig) {
unsigned H = hash_value(Sig.ReturnType);
for (int32_t Param : Sig.ParamTypes)
H = hash_combine(H, Param);
return H;
}
static bool isEqual(const WasmSignature &LHS, const WasmSignature &RHS) {
return LHS == RHS;
}
};
// An init entry to be written to either the synthetic init func or the
// linking metadata.
struct WasmInitEntry {
const Symbol *Sym;
uint32_t Priority;
};
// The writer writes a SymbolTable result to a file.
class Writer {
public:
void run();
private:
void openFile();
uint32_t lookupType(const WasmSignature &Sig);
uint32_t registerType(const WasmSignature &Sig);
void createCtorFunction();
void calculateInitFunctions();
void assignIndexes();
void calculateImports();
void calculateExports();
void assignSymtab();
void calculateTypes();
void createOutputSegments();
void layoutMemory();
void createHeader();
void createSections();
SyntheticSection *createSyntheticSection(uint32_t Type,
StringRef Name = "");
// Builtin sections
void createTypeSection();
void createFunctionSection();
void createTableSection();
void createGlobalSection();
void createExportSection();
void createImportSection();
void createMemorySection();
void createElemSection();
void createCodeSection();
void createDataSection();
// Custom sections
void createRelocSections();
void createLinkingSection();
void createNameSection();
void writeHeader();
void writeSections();
uint64_t FileSize = 0;
uint32_t NumMemoryPages = 0;
std::vector<const WasmSignature *> Types;
DenseMap<WasmSignature, int32_t, WasmSignatureDenseMapInfo> TypeIndices;
std::vector<const Symbol *> ImportedSymbols;
unsigned NumImportedFunctions = 0;
unsigned NumImportedGlobals = 0;
std::vector<Symbol *> ExportedSymbols;
std::vector<const DefinedData *> DefinedFakeGlobals;
std::vector<InputGlobal *> InputGlobals;
std::vector<InputFunction *> InputFunctions;
std::vector<const FunctionSymbol *> IndirectFunctions;
std::vector<const Symbol *> SymtabEntries;
std::vector<WasmInitEntry> InitFunctions;
// Elements that are used to construct the final output
std::string Header;
std::vector<OutputSection *> OutputSections;
std::unique_ptr<FileOutputBuffer> Buffer;
std::vector<OutputSegment *> Segments;
llvm::SmallDenseMap<StringRef, OutputSegment *> SegmentMap;
};
} // anonymous namespace
static void debugPrint(const char *fmt, ...) {
if (!errorHandler().Verbose)
return;
fprintf(stderr, "lld: ");
va_list ap;
va_start(ap, fmt);
vfprintf(stderr, fmt, ap);
va_end(ap);
}
void Writer::createImportSection() {
uint32_t NumImports = ImportedSymbols.size();
if (Config->ImportMemory)
++NumImports;
if (NumImports == 0)
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_IMPORT);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, NumImports, "import count");
if (Config->ImportMemory) {
WasmImport Import;
Import.Module = "env";
Import.Field = "memory";
Import.Kind = WASM_EXTERNAL_MEMORY;
Import.Memory.Flags = 0;
Import.Memory.Initial = NumMemoryPages;
writeImport(OS, Import);
}
for (const Symbol *Sym : ImportedSymbols) {
WasmImport Import;
Import.Module = "env";
Import.Field = Sym->getName();
if (auto *FunctionSym = dyn_cast<FunctionSymbol>(Sym)) {
Import.Kind = WASM_EXTERNAL_FUNCTION;
Import.SigIndex = lookupType(*FunctionSym->getFunctionType());
} else {
auto *GlobalSym = cast<GlobalSymbol>(Sym);
Import.Kind = WASM_EXTERNAL_GLOBAL;
Import.Global = *GlobalSym->getGlobalType();
}
writeImport(OS, Import);
}
}
void Writer::createTypeSection() {
SyntheticSection *Section = createSyntheticSection(WASM_SEC_TYPE);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, Types.size(), "type count");
for (const WasmSignature *Sig : Types)
writeSig(OS, *Sig);
}
void Writer::createFunctionSection() {
if (InputFunctions.empty())
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_FUNCTION);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, InputFunctions.size(), "function count");
for (const InputFunction *Func : InputFunctions)
writeUleb128(OS, lookupType(Func->Signature), "sig index");
}
void Writer::createMemorySection() {
if (Config->ImportMemory)
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_MEMORY);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, 1, "memory count");
writeUleb128(OS, 0, "memory limits flags");
writeUleb128(OS, NumMemoryPages, "initial pages");
}
void Writer::createGlobalSection() {
unsigned NumGlobals = InputGlobals.size() + DefinedFakeGlobals.size();
if (NumGlobals == 0)
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_GLOBAL);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, NumGlobals, "global count");
for (const InputGlobal *G : InputGlobals)
writeGlobal(OS, G->Global);
for (const DefinedData *Sym : DefinedFakeGlobals) {
WasmGlobal Global;
Global.Type = {WASM_TYPE_I32, false};
Global.InitExpr.Opcode = WASM_OPCODE_I32_CONST;
Global.InitExpr.Value.Int32 = Sym->getVirtualAddress();
writeGlobal(OS, Global);
}
}
void Writer::createTableSection() {
// Always output a table section, even if there are no indirect calls.
// There are two reasons for this:
// 1. For executables it is useful to have an empty table slot at 0
// which can be filled with a null function call handler.
// 2. If we don't do this, any program that contains a call_indirect but
// no address-taken function will fail at validation time since it is
// a validation error to include a call_indirect instruction if there
// is not table.
uint32_t TableSize = kInitialTableOffset + IndirectFunctions.size();
SyntheticSection *Section = createSyntheticSection(WASM_SEC_TABLE);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, 1, "table count");
writeU8(OS, WASM_TYPE_ANYFUNC, "table type");
writeUleb128(OS, WASM_LIMITS_FLAG_HAS_MAX, "table flags");
writeUleb128(OS, TableSize, "table initial size");
writeUleb128(OS, TableSize, "table max size");
}
void Writer::createExportSection() {
bool ExportMemory = !Config->Relocatable && !Config->ImportMemory;
uint32_t NumExports = (ExportMemory ? 1 : 0) + ExportedSymbols.size();
if (!NumExports)
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_EXPORT);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, NumExports, "export count");
if (ExportMemory)
writeExport(OS, {"memory", WASM_EXTERNAL_MEMORY, 0});
unsigned FakeGlobalIndex = NumImportedGlobals + InputGlobals.size();
for (const Symbol *Sym : ExportedSymbols) {
StringRef Name = Sym->getName();
WasmExport Export;
DEBUG(dbgs() << "Export: " << Name << "\n");
if (isa<DefinedFunction>(Sym))
Export = {Name, WASM_EXTERNAL_FUNCTION, Sym->getOutputIndex()};
else if (isa<DefinedGlobal>(Sym))
Export = {Name, WASM_EXTERNAL_GLOBAL, Sym->getOutputIndex()};
else if (isa<DefinedData>(Sym))
Export = {Name, WASM_EXTERNAL_GLOBAL, FakeGlobalIndex++};
else
llvm_unreachable("unexpected symbol type");
writeExport(OS, Export);
}
}
void Writer::createElemSection() {
if (IndirectFunctions.empty())
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_ELEM);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, 1, "segment count");
writeUleb128(OS, 0, "table index");
WasmInitExpr InitExpr;
InitExpr.Opcode = WASM_OPCODE_I32_CONST;
InitExpr.Value.Int32 = kInitialTableOffset;
writeInitExpr(OS, InitExpr);
writeUleb128(OS, IndirectFunctions.size(), "elem count");
uint32_t TableIndex = kInitialTableOffset;
for (const FunctionSymbol *Sym : IndirectFunctions) {
assert(Sym->getTableIndex() == TableIndex);
writeUleb128(OS, Sym->getOutputIndex(), "function index");
++TableIndex;
}
}
void Writer::createCodeSection() {
if (InputFunctions.empty())
return;
log("createCodeSection");
auto Section = make<CodeSection>(InputFunctions);
OutputSections.push_back(Section);
}
void Writer::createDataSection() {
if (!Segments.size())
return;
log("createDataSection");
auto Section = make<DataSection>(Segments);
OutputSections.push_back(Section);
}
// Create relocations sections in the final output.
// These are only created when relocatable output is requested.
void Writer::createRelocSections() {
log("createRelocSections");
// Don't use iterator here since we are adding to OutputSection
size_t OrigSize = OutputSections.size();
for (size_t i = 0; i < OrigSize; i++) {
OutputSection *OSec = OutputSections[i];
uint32_t Count = OSec->numRelocations();
if (!Count)
continue;
StringRef Name;
if (OSec->Type == WASM_SEC_DATA)
Name = "reloc.DATA";
else if (OSec->Type == WASM_SEC_CODE)
Name = "reloc.CODE";
else
llvm_unreachable("relocations only supported for code and data");
SyntheticSection *Section = createSyntheticSection(WASM_SEC_CUSTOM, Name);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, OSec->Type, "reloc section");
writeUleb128(OS, Count, "reloc count");
OSec->writeRelocations(OS);
}
}
static uint32_t getWasmFlags(const Symbol *Sym) {
uint32_t Flags = 0;
if (Sym->isLocal())
Flags |= WASM_SYMBOL_BINDING_LOCAL;
if (Sym->isWeak())
Flags |= WASM_SYMBOL_BINDING_WEAK;
if (Sym->isHidden())
Flags |= WASM_SYMBOL_VISIBILITY_HIDDEN;
if (Sym->isUndefined())
Flags |= WASM_SYMBOL_UNDEFINED;
return Flags;
}
// Some synthetic sections (e.g. "name" and "linking") have subsections.
// Just like the synthetic sections themselves these need to be created before
// they can be written out (since they are preceded by their length). This
// class is used to create subsections and then write them into the stream
// of the parent section.
class SubSection {
public:
explicit SubSection(uint32_t Type) : Type(Type) {}
void writeTo(raw_ostream &To) {
OS.flush();
writeUleb128(To, Type, "subsection type");
writeUleb128(To, Body.size(), "subsection size");
To.write(Body.data(), Body.size());
}
private:
uint32_t Type;
std::string Body;
public:
raw_string_ostream OS{Body};
};
// Create the custom "linking" section containing linker metadata.
// This is only created when relocatable output is requested.
void Writer::createLinkingSection() {
SyntheticSection *Section =
createSyntheticSection(WASM_SEC_CUSTOM, "linking");
raw_ostream &OS = Section->getStream();
if (!Config->Relocatable)
return;
if (!SymtabEntries.empty()) {
SubSection Sub(WASM_SYMBOL_TABLE);
writeUleb128(Sub.OS, SymtabEntries.size(), "num symbols");
for (const Symbol *Sym : SymtabEntries) {
assert(Sym->isDefined() || Sym->isUndefined());
WasmSymbolType Kind = Sym->getWasmType();
uint32_t Flags = getWasmFlags(Sym);
writeU8(Sub.OS, Kind, "sym kind");
writeUleb128(Sub.OS, Flags, "sym flags");
switch (Kind) {
case llvm::wasm::WASM_SYMBOL_TYPE_FUNCTION:
case llvm::wasm::WASM_SYMBOL_TYPE_GLOBAL:
writeUleb128(Sub.OS, Sym->getOutputIndex(), "index");
if (Sym->isDefined())
writeStr(Sub.OS, Sym->getName(), "sym name");
break;
case llvm::wasm::WASM_SYMBOL_TYPE_DATA:
writeStr(Sub.OS, Sym->getName(), "sym name");
if (auto *DataSym = dyn_cast<DefinedData>(Sym)) {
writeUleb128(Sub.OS, DataSym->getOutputSegmentIndex(), "index");
writeUleb128(Sub.OS, DataSym->getOutputSegmentOffset(),
"data offset");
writeUleb128(Sub.OS, DataSym->getSize(), "data size");
}
break;
}
}
Sub.writeTo(OS);
}
if (Segments.size()) {
SubSection Sub(WASM_SEGMENT_INFO);
writeUleb128(Sub.OS, Segments.size(), "num data segments");
for (const OutputSegment *S : Segments) {
writeStr(Sub.OS, S->Name, "segment name");
writeUleb128(Sub.OS, S->Alignment, "alignment");
writeUleb128(Sub.OS, 0, "flags");
}
Sub.writeTo(OS);
}
if (!InitFunctions.empty()) {
SubSection Sub(WASM_INIT_FUNCS);
writeUleb128(Sub.OS, InitFunctions.size(), "num init functions");
for (const WasmInitEntry &F : InitFunctions) {
writeUleb128(Sub.OS, F.Priority, "priority");
writeUleb128(Sub.OS, F.Sym->getOutputSymbolIndex(), "function index");
}
Sub.writeTo(OS);
}
struct ComdatEntry { unsigned Kind; uint32_t Index; };
std::map<StringRef,std::vector<ComdatEntry>> Comdats;
for (const InputFunction *F : InputFunctions) {
StringRef Comdat = F->getComdat();
if (!Comdat.empty())
Comdats[Comdat].emplace_back(
ComdatEntry{WASM_COMDAT_FUNCTION, F->getOutputIndex()});
}
for (uint32_t I = 0; I < Segments.size(); ++I) {
const auto &InputSegments = Segments[I]->InputSegments;
if (InputSegments.empty())
continue;
StringRef Comdat = InputSegments[0]->getComdat();
#ifndef NDEBUG
for (const InputSegment *IS : InputSegments)
assert(IS->getComdat() == Comdat);
#endif
if (!Comdat.empty())
Comdats[Comdat].emplace_back(ComdatEntry{WASM_COMDAT_DATA, I});
}
if (!Comdats.empty()) {
SubSection Sub(WASM_COMDAT_INFO);
writeUleb128(Sub.OS, Comdats.size(), "num comdats");
for (const auto &C : Comdats) {
writeStr(Sub.OS, C.first, "comdat name");
writeUleb128(Sub.OS, 0, "comdat flags"); // flags for future use
writeUleb128(Sub.OS, C.second.size(), "num entries");
for (const ComdatEntry &Entry : C.second) {
writeU8(Sub.OS, Entry.Kind, "entry kind");
writeUleb128(Sub.OS, Entry.Index, "entry index");
}
}
Sub.writeTo(OS);
}
}
// Create the custom "name" section containing debug symbol names.
void Writer::createNameSection() {
unsigned NumNames = NumImportedFunctions;
for (const InputFunction *F : InputFunctions)
if (!F->getName().empty())
++NumNames;
if (NumNames == 0)
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_CUSTOM, "name");
SubSection Sub(WASM_NAMES_FUNCTION);
writeUleb128(Sub.OS, NumNames, "name count");
// Names must appear in function index order. As it happens ImportedSymbols
// and InputFunctions are numbered in order with imported functions coming
// first.
for (const Symbol *S : ImportedSymbols) {
if (!isa<FunctionSymbol>(S))
continue;
writeUleb128(Sub.OS, S->getOutputIndex(), "import index");
writeStr(Sub.OS, S->getName(), "symbol name");
}
for (const InputFunction *F : InputFunctions) {
if (!F->getName().empty()) {
writeUleb128(Sub.OS, F->getOutputIndex(), "func index");
writeStr(Sub.OS, F->getName(), "symbol name");
}
}
Sub.writeTo(Section->getStream());
}
void Writer::writeHeader() {
memcpy(Buffer->getBufferStart(), Header.data(), Header.size());
}
void Writer::writeSections() {
uint8_t *Buf = Buffer->getBufferStart();
parallelForEach(OutputSections, [Buf](OutputSection *S) { S->writeTo(Buf); });
}
// Fix the memory layout of the output binary. This assigns memory offsets
// to each of the input data sections as well as the explicit stack region.
// The memory layout is as follows, from low to high.
// - initialized data (starting at Config->GlobalBase)
// - BSS data (not currently implemented in llvm)
// - explicit stack (Config->ZStackSize)
// - heap start / unallocated
void Writer::layoutMemory() {
uint32_t MemoryPtr = 0;
MemoryPtr = Config->GlobalBase;
debugPrint("mem: global base = %d\n", Config->GlobalBase);
createOutputSegments();
// Arbitrarily set __dso_handle handle to point to the start of the data
// segments.
if (WasmSym::DsoHandle)
WasmSym::DsoHandle->setVirtualAddress(MemoryPtr);
for (OutputSegment *Seg : Segments) {
MemoryPtr = alignTo(MemoryPtr, Seg->Alignment);
Seg->StartVA = MemoryPtr;
debugPrint("mem: %-15s offset=%-8d size=%-8d align=%d\n",
Seg->Name.str().c_str(), MemoryPtr, Seg->Size, Seg->Alignment);
MemoryPtr += Seg->Size;
}
// TODO: Add .bss space here.
if (WasmSym::DataEnd)
WasmSym::DataEnd->setVirtualAddress(MemoryPtr);
debugPrint("mem: static data = %d\n", MemoryPtr - Config->GlobalBase);
// Stack comes after static data and bss
if (!Config->Relocatable) {
MemoryPtr = alignTo(MemoryPtr, kStackAlignment);
if (Config->ZStackSize != alignTo(Config->ZStackSize, kStackAlignment))
error("stack size must be " + Twine(kStackAlignment) + "-byte aligned");
debugPrint("mem: stack size = %d\n", Config->ZStackSize);
debugPrint("mem: stack base = %d\n", MemoryPtr);
MemoryPtr += Config->ZStackSize;
WasmSym::StackPointer->Global->Global.InitExpr.Value.Int32 = MemoryPtr;
debugPrint("mem: stack top = %d\n", MemoryPtr);
// Set `__heap_base` to directly follow the end of the stack. We don't
// allocate any heap memory up front, but instead really on the malloc/brk
// implementation growing the memory at runtime.
WasmSym::HeapBase->setVirtualAddress(MemoryPtr);
debugPrint("mem: heap base = %d\n", MemoryPtr);
}
uint32_t MemSize = alignTo(MemoryPtr, WasmPageSize);
NumMemoryPages = MemSize / WasmPageSize;
debugPrint("mem: total pages = %d\n", NumMemoryPages);
}
SyntheticSection *Writer::createSyntheticSection(uint32_t Type,
StringRef Name) {
auto Sec = make<SyntheticSection>(Type, Name);
log("createSection: " + toString(*Sec));
OutputSections.push_back(Sec);
return Sec;
}
void Writer::createSections() {
// Known sections
createTypeSection();
createImportSection();
createFunctionSection();
createTableSection();
createMemorySection();
createGlobalSection();
createExportSection();
createElemSection();
createCodeSection();
createDataSection();
// Custom sections
if (Config->Relocatable) {
createLinkingSection();
createRelocSections();
}
if (!Config->StripDebug && !Config->StripAll)
createNameSection();
for (OutputSection *S : OutputSections) {
S->setOffset(FileSize);
S->finalizeContents();
FileSize += S->getSize();
}
}
void Writer::calculateImports() {
for (Symbol *Sym : Symtab->getSymbols()) {
if (!Sym->isUndefined())
continue;
if (isa<DataSymbol>(Sym))
continue;
if (Sym->isWeak() && !Config->Relocatable)
continue;
DEBUG(dbgs() << "import: " << Sym->getName() << "\n");
Sym->setOutputIndex(ImportedSymbols.size());
ImportedSymbols.emplace_back(Sym);
if (isa<FunctionSymbol>(Sym))
++NumImportedFunctions;
else
++NumImportedGlobals;
}
}
void Writer::calculateExports() {
if (Config->Relocatable)
return;
for (Symbol *Sym : Symtab->getSymbols()) {
if (!Sym->isDefined())
continue;
if (Sym->isHidden() || Sym->isLocal())
continue;
if (!Sym->isLive())
continue;
DEBUG(dbgs() << "exporting sym: " << Sym->getName() << "\n");
if (auto *D = dyn_cast<DefinedData>(Sym))
DefinedFakeGlobals.emplace_back(D);
ExportedSymbols.emplace_back(Sym);
}
}
void Writer::assignSymtab() {
if (!Config->Relocatable)
return;
unsigned SymbolIndex = SymtabEntries.size();
for (ObjFile *File : Symtab->ObjectFiles) {
DEBUG(dbgs() << "Symtab entries: " << File->getName() << "\n");
for (Symbol *Sym : File->getSymbols()) {
if (Sym->getFile() != File)
continue;
// (Since this is relocatable output, GC is not performed so symbols must
// be live.)
assert(Sym->isLive());
Sym->setOutputSymbolIndex(SymbolIndex++);
SymtabEntries.emplace_back(Sym);
}
}
// For the moment, relocatable output doesn't contain any synthetic functions,
// so no need to look through the Symtab for symbols not referenced by
// Symtab->ObjectFiles.
}
uint32_t Writer::lookupType(const WasmSignature &Sig) {
auto It = TypeIndices.find(Sig);
if (It == TypeIndices.end()) {
error("type not found: " + toString(Sig));
return 0;
}
return It->second;
}
uint32_t Writer::registerType(const WasmSignature &Sig) {
auto Pair = TypeIndices.insert(std::make_pair(Sig, Types.size()));
if (Pair.second) {
DEBUG(dbgs() << "type " << toString(Sig) << "\n");
Types.push_back(&Sig);
}
return Pair.first->second;
}
void Writer::calculateTypes() {
// The output type section is the union of the following sets:
// 1. Any signature used in the TYPE relocation
// 2. The signatures of all imported functions
// 3. The signatures of all defined functions
for (ObjFile *File : Symtab->ObjectFiles) {
ArrayRef<WasmSignature> Types = File->getWasmObj()->types();
for (uint32_t I = 0; I < Types.size(); I++)
if (File->TypeIsUsed[I])
File->TypeMap[I] = registerType(Types[I]);
}
for (const Symbol *Sym : ImportedSymbols)
if (auto *F = dyn_cast<FunctionSymbol>(Sym))
registerType(*F->getFunctionType());
for (const InputFunction *F : InputFunctions)
registerType(F->Signature);
}
void Writer::assignIndexes() {
uint32_t FunctionIndex = NumImportedFunctions + InputFunctions.size();
for (ObjFile *File : Symtab->ObjectFiles) {
DEBUG(dbgs() << "Functions: " << File->getName() << "\n");
for (InputFunction *Func : File->Functions) {
if (!Func->Live)
continue;
InputFunctions.emplace_back(Func);
Func->setOutputIndex(FunctionIndex++);
}
}
uint32_t TableIndex = kInitialTableOffset;
auto HandleRelocs = [&](InputChunk *Chunk) {
if (!Chunk->Live)
return;
ObjFile *File = Chunk->File;
ArrayRef<WasmSignature> Types = File->getWasmObj()->types();
for (const WasmRelocation &Reloc : Chunk->getRelocations()) {
if (Reloc.Type == R_WEBASSEMBLY_TABLE_INDEX_I32 ||
Reloc.Type == R_WEBASSEMBLY_TABLE_INDEX_SLEB) {
FunctionSymbol *Sym = File->getFunctionSymbol(Reloc.Index);
if (Sym->hasTableIndex() || !Sym->hasOutputIndex())
continue;
Sym->setTableIndex(TableIndex++);
IndirectFunctions.emplace_back(Sym);
} else if (Reloc.Type == R_WEBASSEMBLY_TYPE_INDEX_LEB) {
// Mark target type as live
File->TypeMap[Reloc.Index] = registerType(Types[Reloc.Index]);
File->TypeIsUsed[Reloc.Index] = true;
} else if (Reloc.Type == R_WEBASSEMBLY_GLOBAL_INDEX_LEB) {
// Mark target global as live
GlobalSymbol *Sym = File->getGlobalSymbol(Reloc.Index);
if (auto *G = dyn_cast<DefinedGlobal>(Sym)) {
DEBUG(dbgs() << "marking global live: " << Sym->getName() << "\n");
G->Global->Live = true;
}
}
}
};
for (ObjFile *File : Symtab->ObjectFiles) {
DEBUG(dbgs() << "Handle relocs: " << File->getName() << "\n");
for (InputChunk *Chunk : File->Functions)
HandleRelocs(Chunk);
for (InputChunk *Chunk : File->Segments)
HandleRelocs(Chunk);
}
uint32_t GlobalIndex = NumImportedGlobals + InputGlobals.size();
auto AddDefinedGlobal = [&](InputGlobal *Global) {
if (Global->Live) {
DEBUG(dbgs() << "AddDefinedGlobal: " << GlobalIndex << "\n");
Global->setOutputIndex(GlobalIndex++);
InputGlobals.push_back(Global);
}
};
if (WasmSym::StackPointer)
AddDefinedGlobal(WasmSym::StackPointer->Global);
for (ObjFile *File : Symtab->ObjectFiles) {
DEBUG(dbgs() << "Globals: " << File->getName() << "\n");
for (InputGlobal *Global : File->Globals)
AddDefinedGlobal(Global);
}
}
static StringRef getOutputDataSegmentName(StringRef Name) {
if (Config->Relocatable)
return Name;
if (Name.startswith(".text."))
return ".text";
if (Name.startswith(".data."))
return ".data";
if (Name.startswith(".bss."))
return ".bss";
return Name;
}
void Writer::createOutputSegments() {
for (ObjFile *File : Symtab->ObjectFiles) {
for (InputSegment *Segment : File->Segments) {
if (!Segment->Live)
continue;
StringRef Name = getOutputDataSegmentName(Segment->getName());
OutputSegment *&S = SegmentMap[Name];
if (S == nullptr) {
DEBUG(dbgs() << "new segment: " << Name << "\n");
S = make<OutputSegment>(Name, Segments.size());
Segments.push_back(S);
}
S->addInputSegment(Segment);
DEBUG(dbgs() << "added data: " << Name << ": " << S->Size << "\n");
}
}
}
static const int OPCODE_CALL = 0x10;
static const int OPCODE_END = 0xb;
// Create synthetic "__wasm_call_ctors" function based on ctor functions
// in input object.
void Writer::createCtorFunction() {
uint32_t FunctionIndex = NumImportedFunctions + InputFunctions.size();
// First write the body's contents to a string.
std::string BodyContent;
{
raw_string_ostream OS(BodyContent);
writeUleb128(OS, 0, "num locals");
for (const WasmInitEntry &F : InitFunctions) {
writeU8(OS, OPCODE_CALL, "CALL");
writeUleb128(OS, F.Sym->getOutputIndex(), "function index");
}
writeU8(OS, OPCODE_END, "END");
}
// Once we know the size of the body we can create the final function body
std::string FunctionBody;
{
raw_string_ostream OS(FunctionBody);
writeUleb128(OS, BodyContent.size(), "function size");
OS << BodyContent;
}
const WasmSignature *Sig = WasmSym::CallCtors->getFunctionType();
SyntheticFunction *F = make<SyntheticFunction>(
*Sig, toArrayRef(Saver.save(FunctionBody)),
WasmSym::CallCtors->getName());
F->setOutputIndex(FunctionIndex);
F->Live = true;
WasmSym::CallCtors->Function = F;
InputFunctions.emplace_back(F);
}
// Populate InitFunctions vector with init functions from all input objects.
// This is then used either when creating the output linking section or to
// synthesize the "__wasm_call_ctors" function.
void Writer::calculateInitFunctions() {
for (ObjFile *File : Symtab->ObjectFiles) {
const WasmLinkingData &L = File->getWasmObj()->linkingData();
for (const WasmInitFunc &F : L.InitFunctions) {
FunctionSymbol *Sym = File->getFunctionSymbol(F.Symbol);
if (*Sym->getFunctionType() != WasmSignature{{}, WASM_TYPE_NORESULT})
error("invalid signature for init func: " + toString(*Sym));
InitFunctions.emplace_back(WasmInitEntry{Sym, F.Priority});
}
}
// Sort in order of priority (lowest first) so that they are called
// in the correct order.
std::stable_sort(InitFunctions.begin(), InitFunctions.end(),
[](const WasmInitEntry &L, const WasmInitEntry &R) {
return L.Priority < R.Priority;
});
}
void Writer::run() {
if (Config->Relocatable)
Config->GlobalBase = 0;
log("-- calculateImports");
calculateImports();
log("-- assignIndexes");
assignIndexes();
log("-- calculateInitFunctions");
calculateInitFunctions();
if (!Config->Relocatable)
createCtorFunction();
log("-- calculateTypes");
calculateTypes();
log("-- layoutMemory");
layoutMemory();
log("-- calculateExports");
calculateExports();
log("-- assignSymtab");
assignSymtab();
if (errorHandler().Verbose) {
log("Defined Functions: " + Twine(InputFunctions.size()));
log("Defined Globals : " + Twine(InputGlobals.size()));
log("Function Imports : " + Twine(NumImportedFunctions));
log("Global Imports : " + Twine(NumImportedGlobals));
for (ObjFile *File : Symtab->ObjectFiles)
File->dumpInfo();
}
createHeader();
log("-- createSections");
createSections();
log("-- openFile");
openFile();
if (errorCount())
return;
writeHeader();
log("-- writeSections");
writeSections();
if (errorCount())
return;
if (Error E = Buffer->commit())
fatal("failed to write the output file: " + toString(std::move(E)));
}
// Open a result file.
void Writer::openFile() {
log("writing: " + Config->OutputFile);
Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
FileOutputBuffer::create(Config->OutputFile, FileSize,
FileOutputBuffer::F_executable);
if (!BufferOrErr)
error("failed to open " + Config->OutputFile + ": " +
toString(BufferOrErr.takeError()));
else
Buffer = std::move(*BufferOrErr);
}
void Writer::createHeader() {
raw_string_ostream OS(Header);
writeBytes(OS, WasmMagic, sizeof(WasmMagic), "wasm magic");
writeU32(OS, WasmVersion, "wasm version");
OS.flush();
FileSize += Header.size();
}
void lld::wasm::writeResult() { Writer().run(); }