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d15a4154a8
llvm-capstone/lld/wasm/Writer.cpp
Sam Clegg d15a4154a8 [WebAssembly] Don't mark lazy symbols as IsUsedInRegularObj 
This matches the ELF does.  Update the comment in ELF/Symbols.h and
duplicate it in wasm/Symbols.h

This a followup on rL355580 and rL355577.

Differential Revision: https://reviews.llvm.org/D59075

llvm-svn: 355737
2019-03-08 21:10:48 +00:00

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//===- Writer.cpp ---------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "Writer.h"
#include "Config.h"
#include "InputChunks.h"
#include "InputEvent.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/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/BinaryFormat/Wasm.h"
#include "llvm/Object/WasmTraits.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 StackAlignment = 16;
static constexpr const char *FunctionTableName = "__indirect_function_table";
const char *lld::wasm::DefaultModule = "env";
namespace {
// An init entry to be written to either the synthetic init func or the
// linking metadata.
struct WasmInitEntry {
const FunctionSymbol *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 calculateCustomSections();
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 createEventSection();
void createExportSection();
void createImportSection();
void createMemorySection();
void createElemSection();
void createCodeSection();
void createDataSection();
void createCustomSections();
// Custom sections
void createDylinkSection();
void createRelocSections();
void createLinkingSection();
void createNameSection();
void createProducersSection();
void writeHeader();
void writeSections();
uint64_t FileSize = 0;
uint32_t TableBase = 0;
uint32_t NumMemoryPages = 0;
uint32_t MaxMemoryPages = 0;
// Memory size and aligment. Written to the "dylink" section
// when build with -shared or -pie.
uint32_t MemAlign = 0;
uint32_t MemSize = 0;
std::vector<const WasmSignature *> Types;
DenseMap<WasmSignature, int32_t> TypeIndices;
std::vector<const Symbol *> ImportedSymbols;
unsigned NumImportedFunctions = 0;
unsigned NumImportedGlobals = 0;
unsigned NumImportedEvents = 0;
std::vector<WasmExport> Exports;
std::vector<const DefinedData *> DefinedFakeGlobals;
std::vector<InputGlobal *> InputGlobals;
std::vector<InputFunction *> InputFunctions;
std::vector<InputEvent *> InputEvents;
std::vector<const FunctionSymbol *> IndirectFunctions;
std::vector<const Symbol *> SymtabEntries;
std::vector<WasmInitEntry> InitFunctions;
llvm::StringMap<std::vector<InputSection *>> CustomSectionMapping;
llvm::StringMap<SectionSymbol *> CustomSectionSymbols;
// 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
void Writer::createImportSection() {
uint32_t NumImports = ImportedSymbols.size();
if (Config->ImportMemory)
++NumImports;
if (Config->ImportTable)
++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 = DefaultModule;
Import.Field = "memory";
Import.Kind = WASM_EXTERNAL_MEMORY;
Import.Memory.Flags = 0;
Import.Memory.Initial = NumMemoryPages;
if (MaxMemoryPages != 0) {
Import.Memory.Flags |= WASM_LIMITS_FLAG_HAS_MAX;
Import.Memory.Maximum = MaxMemoryPages;
}
if (Config->SharedMemory)
Import.Memory.Flags |= WASM_LIMITS_FLAG_IS_SHARED;
writeImport(OS, Import);
}
if (Config->ImportTable) {
uint32_t TableSize = TableBase + IndirectFunctions.size();
WasmImport Import;
Import.Module = DefaultModule;
Import.Field = FunctionTableName;
Import.Kind = WASM_EXTERNAL_TABLE;
Import.Table.ElemType = WASM_TYPE_FUNCREF;
Import.Table.Limits = {0, TableSize, 0};
writeImport(OS, Import);
}
for (const Symbol *Sym : ImportedSymbols) {
WasmImport Import;
if (auto *F = dyn_cast<UndefinedFunction>(Sym)) {
Import.Field = F->ImportName;
Import.Module = F->ImportModule;
} else if (auto *G = dyn_cast<UndefinedGlobal>(Sym)) {
Import.Field = G->ImportName;
Import.Module = G->ImportModule;
} else {
Import.Field = Sym->getName();
Import.Module = DefaultModule;
}
if (auto *FunctionSym = dyn_cast<FunctionSymbol>(Sym)) {
Import.Kind = WASM_EXTERNAL_FUNCTION;
Import.SigIndex = lookupType(*FunctionSym->Signature);
} else if (auto *GlobalSym = dyn_cast<GlobalSymbol>(Sym)) {
Import.Kind = WASM_EXTERNAL_GLOBAL;
Import.Global = *GlobalSym->getGlobalType();
} else {
auto *EventSym = cast<EventSymbol>(Sym);
Import.Kind = WASM_EXTERNAL_EVENT;
Import.Event.Attribute = EventSym->getEventType()->Attribute;
Import.Event.SigIndex = lookupType(*EventSym->Signature);
}
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();
bool HasMax = MaxMemoryPages != 0;
writeUleb128(OS, 1, "memory count");
unsigned Flags = 0;
if (HasMax)
Flags |= WASM_LIMITS_FLAG_HAS_MAX;
if (Config->SharedMemory)
Flags |= WASM_LIMITS_FLAG_IS_SHARED;
writeUleb128(OS, Flags, "memory limits flags");
writeUleb128(OS, NumMemoryPages, "initial pages");
if (HasMax)
writeUleb128(OS, MaxMemoryPages, "max 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);
}
}
// The event section contains a list of declared wasm events associated with the
// module. Currently the only supported event kind is exceptions. A single event
// entry represents a single event with an event tag. All C++ exceptions are
// represented by a single event. An event entry in this section contains
// information on what kind of event it is (e.g. exception) and the type of
// values contained in a single event object. (In wasm, an event can contain
// multiple values of primitive types. But for C++ exceptions, we just throw a
// pointer which is an i32 value (for wasm32 architecture), so the signature of
// C++ exception is (i32)->(void), because all event types are assumed to have
// void return type to share WasmSignature with functions.)
void Writer::createEventSection() {
unsigned NumEvents = InputEvents.size();
if (NumEvents == 0)
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_EVENT);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, NumEvents, "event count");
for (InputEvent *E : InputEvents) {
E->Event.Type.SigIndex = lookupType(E->Signature);
writeEvent(OS, E->Event);
}
}
void Writer::createTableSection() {
if (Config->ImportTable)
return;
// Always output a table section (or table import), 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 = TableBase + IndirectFunctions.size();
SyntheticSection *Section = createSyntheticSection(WASM_SEC_TABLE);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, 1, "table count");
WasmLimits Limits = {WASM_LIMITS_FLAG_HAS_MAX, TableSize, TableSize};
writeTableType(OS, WasmTable{WASM_TYPE_FUNCREF, Limits});
}
void Writer::createExportSection() {
if (!Exports.size())
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_EXPORT);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, Exports.size(), "export count");
for (const WasmExport &Export : Exports)
writeExport(OS, Export);
}
void Writer::calculateCustomSections() {
log("calculateCustomSections");
bool StripDebug = Config->StripDebug || Config->StripAll;
for (ObjFile *File : Symtab->ObjectFiles) {
for (InputSection *Section : File->CustomSections) {
StringRef Name = Section->getName();
// These custom sections are known the linker and synthesized rather than
// blindly copied
if (Name == "linking" || Name == "name" || Name == "producers" ||
Name.startswith("reloc."))
continue;
// .. or it is a debug section
if (StripDebug && Name.startswith(".debug_"))
continue;
CustomSectionMapping[Name].push_back(Section);
}
}
}
void Writer::createCustomSections() {
log("createCustomSections");
for (auto &Pair : CustomSectionMapping) {
StringRef Name = Pair.first();
auto P = CustomSectionSymbols.find(Name);
if (P != CustomSectionSymbols.end()) {
uint32_t SectionIndex = OutputSections.size();
P->second->setOutputSectionIndex(SectionIndex);
}
LLVM_DEBUG(dbgs() << "createCustomSection: " << Name << "\n");
OutputSections.push_back(make<CustomSection>(Name, Pair.second));
}
}
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;
if (Config->Pic) {
InitExpr.Opcode = WASM_OPCODE_GLOBAL_GET;
InitExpr.Value.Global = WasmSym::TableBase->getGlobalIndex();
} else {
InitExpr.Opcode = WASM_OPCODE_I32_CONST;
InitExpr.Value.Int32 = TableBase;
}
writeInitExpr(OS, InitExpr);
writeUleb128(OS, IndirectFunctions.size(), "elem count");
uint32_t TableIndex = TableBase;
for (const FunctionSymbol *Sym : IndirectFunctions) {
assert(Sym->getTableIndex() == TableIndex);
writeUleb128(OS, Sym->getFunctionIndex(), "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 if (OSec->Type == WASM_SEC_CUSTOM)
Name = Saver.save("reloc." + OSec->Name);
else
llvm_unreachable(
"relocations only supported for code, data, or custom sections");
SyntheticSection *Section = createSyntheticSection(WASM_SEC_CUSTOM, Name);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, I, "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;
if (auto *F = dyn_cast<UndefinedFunction>(Sym)) {
if (F->getName() != F->ImportName)
Flags |= WASM_SYMBOL_EXPLICIT_NAME;
} else if (auto *G = dyn_cast<UndefinedGlobal>(Sym)) {
if (G->getName() != G->ImportName)
Flags |= WASM_SYMBOL_EXPLICIT_NAME;
}
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 "dylink" section containing information for the dynamic
// linker.
// See
// https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md
void Writer::createDylinkSection() {
SyntheticSection *Section = createSyntheticSection(WASM_SEC_CUSTOM, "dylink");
raw_ostream &OS = Section->getStream();
writeUleb128(OS, MemSize, "MemSize");
writeUleb128(OS, MemAlign, "MemAlign");
writeUleb128(OS, IndirectFunctions.size(), "TableSize");
writeUleb128(OS, 0, "TableAlign");
writeUleb128(OS, 0, "Needed"); // TODO: Support "needed" shared libraries
}
// 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();
writeUleb128(OS, WasmMetadataVersion, "Version");
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");
if (auto *F = dyn_cast<FunctionSymbol>(Sym)) {
writeUleb128(Sub.OS, F->getFunctionIndex(), "index");
if (Sym->isDefined() ||
(Flags & WASM_SYMBOL_EXPLICIT_NAME) != 0)
writeStr(Sub.OS, Sym->getName(), "sym name");
} else if (auto *G = dyn_cast<GlobalSymbol>(Sym)) {
writeUleb128(Sub.OS, G->getGlobalIndex(), "index");
if (Sym->isDefined() ||
(Flags & WASM_SYMBOL_EXPLICIT_NAME) != 0)
writeStr(Sub.OS, Sym->getName(), "sym name");
} else if (auto *E = dyn_cast<EventSymbol>(Sym)) {
writeUleb128(Sub.OS, E->getEventIndex(), "index");
if (Sym->isDefined() ||
(Flags & WASM_SYMBOL_EXPLICIT_NAME) != 0)
writeStr(Sub.OS, Sym->getName(), "sym name");
} else if (isa<DataSymbol>(Sym)) {
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");
}
} else {
auto *S = cast<SectionSymbol>(Sym);
writeUleb128(Sub.OS, S->getOutputSectionIndex(), "sym section index");
}
}
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->getComdatName();
if (!Comdat.empty())
Comdats[Comdat].emplace_back(
ComdatEntry{WASM_COMDAT_FUNCTION, F->getFunctionIndex()});
}
for (uint32_t I = 0; I < Segments.size(); ++I) {
const auto &InputSegments = Segments[I]->InputSegments;
if (InputSegments.empty())
continue;
StringRef Comdat = InputSegments[0]->getComdatName();
#ifndef NDEBUG
for (const InputSegment *IS : InputSegments)
assert(IS->getComdatName() == 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() || !F->getDebugName().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 (auto *F = dyn_cast<FunctionSymbol>(S)) {
writeUleb128(Sub.OS, F->getFunctionIndex(), "func index");
writeStr(Sub.OS, toString(*S), "symbol name");
}
}
for (const InputFunction *F : InputFunctions) {
if (!F->getName().empty()) {
writeUleb128(Sub.OS, F->getFunctionIndex(), "func index");
if (!F->getDebugName().empty()) {
writeStr(Sub.OS, F->getDebugName(), "symbol name");
} else {
writeStr(Sub.OS, maybeDemangleSymbol(F->getName()), "symbol name");
}
}
}
Sub.writeTo(Section->getStream());
}
void Writer::createProducersSection() {
SmallVector<std::pair<std::string, std::string>, 8> Languages;
SmallVector<std::pair<std::string, std::string>, 8> Tools;
SmallVector<std::pair<std::string, std::string>, 8> SDKs;
for (ObjFile *File : Symtab->ObjectFiles) {
const WasmProducerInfo &Info = File->getWasmObj()->getProducerInfo();
for (auto &Producers : {std::make_pair(&Info.Languages, &Languages),
std::make_pair(&Info.Tools, &Tools),
std::make_pair(&Info.SDKs, &SDKs)})
for (auto &Producer : *Producers.first)
if (Producers.second->end() ==
std::find_if(Producers.second->begin(), Producers.second->end(),
[&](std::pair<std::string, std::string> Seen) {
return Seen.first == Producer.first;
}))
Producers.second->push_back(Producer);
}
int FieldCount =
int(!Languages.empty()) + int(!Tools.empty()) + int(!SDKs.empty());
if (FieldCount == 0)
return;
SyntheticSection *Section =
createSyntheticSection(WASM_SEC_CUSTOM, "producers");
auto &OS = Section->getStream();
writeUleb128(OS, FieldCount, "field count");
for (auto &Field :
{std::make_pair("language", Languages),
std::make_pair("processed-by", Tools), std::make_pair("sdk", SDKs)}) {
if (Field.second.empty())
continue;
writeStr(OS, Field.first, "field name");
writeUleb128(OS, Field.second.size(), "number of entries");
for (auto &Entry : Field.second) {
writeStr(OS, Entry.first, "producer name");
writeStr(OS, Entry.second, "producer version");
}
}
}
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 default 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
//
// The --stack-first option means that stack is placed before any static data.
// This can be useful since it means that stack overflow traps immediately
// rather than overwriting global data, but also increases code size since all
// static data loads and stores requires larger offsets.
void Writer::layoutMemory() {
createOutputSegments();
uint32_t MemoryPtr = 0;
auto PlaceStack = [&]() {
if (Config->Relocatable || Config->Shared)
return;
MemoryPtr = alignTo(MemoryPtr, StackAlignment);
if (Config->ZStackSize != alignTo(Config->ZStackSize, StackAlignment))
error("stack size must be " + Twine(StackAlignment) + "-byte aligned");
log("mem: stack size = " + Twine(Config->ZStackSize));
log("mem: stack base = " + Twine(MemoryPtr));
MemoryPtr += Config->ZStackSize;
auto *SP = cast<DefinedGlobal>(WasmSym::StackPointer);
SP->Global->Global.InitExpr.Value.Int32 = MemoryPtr;
log("mem: stack top = " + Twine(MemoryPtr));
};
if (Config->StackFirst) {
PlaceStack();
} else {
MemoryPtr = Config->GlobalBase;
log("mem: global base = " + Twine(Config->GlobalBase));
}
uint32_t DataStart = MemoryPtr;
// Arbitrarily set __dso_handle handle to point to the start of the data
// segments.
if (WasmSym::DsoHandle)
WasmSym::DsoHandle->setVirtualAddress(DataStart);
MemAlign = 0;
for (OutputSegment *Seg : Segments) {
MemAlign = std::max(MemAlign, Seg->Alignment);
MemoryPtr = alignTo(MemoryPtr, 1ULL << Seg->Alignment);
Seg->StartVA = MemoryPtr;
log(formatv("mem: {0,-15} offset={1,-8} size={2,-8} align={3}", Seg->Name,
MemoryPtr, Seg->Size, Seg->Alignment));
MemoryPtr += Seg->Size;
}
// TODO: Add .bss space here.
if (WasmSym::DataEnd)
WasmSym::DataEnd->setVirtualAddress(MemoryPtr);
log("mem: static data = " + Twine(MemoryPtr - DataStart));
if (Config->Shared) {
MemSize = MemoryPtr;
return;
}
if (!Config->StackFirst)
PlaceStack();
// Set `__heap_base` to directly follow the end of the stack or global data.
// The fact that this comes last means that a malloc/brk implementation
// can grow the heap at runtime.
if (!Config->Relocatable) {
WasmSym::HeapBase->setVirtualAddress(MemoryPtr);
log("mem: heap base = " + Twine(MemoryPtr));
}
if (Config->InitialMemory != 0) {
if (Config->InitialMemory != alignTo(Config->InitialMemory, WasmPageSize))
error("initial memory must be " + Twine(WasmPageSize) + "-byte aligned");
if (MemoryPtr > Config->InitialMemory)
error("initial memory too small, " + Twine(MemoryPtr) + " bytes needed");
else
MemoryPtr = Config->InitialMemory;
}
MemSize = MemoryPtr;
NumMemoryPages = alignTo(MemoryPtr, WasmPageSize) / WasmPageSize;
log("mem: total pages = " + Twine(NumMemoryPages));
if (Config->MaxMemory != 0) {
if (Config->MaxMemory != alignTo(Config->MaxMemory, WasmPageSize))
error("maximum memory must be " + Twine(WasmPageSize) + "-byte aligned");
if (MemoryPtr > Config->MaxMemory)
error("maximum memory too small, " + Twine(MemoryPtr) + " bytes needed");
MaxMemoryPages = Config->MaxMemory / WasmPageSize;
log("mem: max pages = " + Twine(MaxMemoryPages));
}
}
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
if (Config->Pic)
createDylinkSection();
createTypeSection();
createImportSection();
createFunctionSection();
createTableSection();
createMemorySection();
createGlobalSection();
createEventSection();
createExportSection();
createElemSection();
createCodeSection();
createDataSection();
createCustomSections();
// Custom sections
if (Config->Relocatable) {
createLinkingSection();
createRelocSections();
}
if (!Config->StripDebug && !Config->StripAll)
createNameSection();
if (!Config->StripAll)
createProducersSection();
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;
if (!Sym->isLive())
continue;
if (!Sym->IsUsedInRegularObj)
continue;
LLVM_DEBUG(dbgs() << "import: " << Sym->getName() << "\n");
ImportedSymbols.emplace_back(Sym);
if (auto *F = dyn_cast<FunctionSymbol>(Sym))
F->setFunctionIndex(NumImportedFunctions++);
else if (auto *G = dyn_cast<GlobalSymbol>(Sym))
G->setGlobalIndex(NumImportedGlobals++);
else
cast<EventSymbol>(Sym)->setEventIndex(NumImportedEvents++);
}
}
void Writer::calculateExports() {
if (Config->Relocatable)
return;
if (!Config->Relocatable && !Config->ImportMemory)
Exports.push_back(WasmExport{"memory", WASM_EXTERNAL_MEMORY, 0});
if (!Config->Relocatable && Config->ExportTable)
Exports.push_back(WasmExport{FunctionTableName, WASM_EXTERNAL_TABLE, 0});
unsigned FakeGlobalIndex = NumImportedGlobals + InputGlobals.size();
for (Symbol *Sym : Symtab->getSymbols()) {
if (!Sym->isExported())
continue;
if (!Sym->isLive())
continue;
StringRef Name = Sym->getName();
WasmExport Export;
if (auto *F = dyn_cast<DefinedFunction>(Sym)) {
Export = {Name, WASM_EXTERNAL_FUNCTION, F->getFunctionIndex()};
} else if (auto *G = dyn_cast<DefinedGlobal>(Sym)) {
// TODO(sbc): Remove this check once to mutable global proposal is
// implement in all major browsers.
// See: https://github.com/WebAssembly/mutable-global
if (G->getGlobalType()->Mutable) {
// Only the __stack_pointer should ever be create as mutable.
assert(G == WasmSym::StackPointer);
continue;
}
Export = {Name, WASM_EXTERNAL_GLOBAL, G->getGlobalIndex()};
} else if (auto *E = dyn_cast<DefinedEvent>(Sym)) {
Export = {Name, WASM_EXTERNAL_EVENT, E->getEventIndex()};
} else {
auto *D = cast<DefinedData>(Sym);
DefinedFakeGlobals.emplace_back(D);
Export = {Name, WASM_EXTERNAL_GLOBAL, FakeGlobalIndex++};
}
LLVM_DEBUG(dbgs() << "Export: " << Name << "\n");
Exports.push_back(Export);
}
}
void Writer::assignSymtab() {
if (!Config->Relocatable)
return;
StringMap<uint32_t> SectionSymbolIndices;
unsigned SymbolIndex = SymtabEntries.size();
auto AddSymbol = [&](Symbol *Sym) {
if (auto *S = dyn_cast<SectionSymbol>(Sym)) {
StringRef Name = S->getName();
if (CustomSectionMapping.count(Name) == 0)
return;
auto SSI = SectionSymbolIndices.find(Name);
if (SSI != SectionSymbolIndices.end()) {
Sym->setOutputSymbolIndex(SSI->second);
return;
}
SectionSymbolIndices[Name] = SymbolIndex;
CustomSectionSymbols[Name] = cast<SectionSymbol>(Sym);
Sym->markLive();
}
// (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 (Symbol *Sym : Symtab->getSymbols())
if (Sym->IsUsedInRegularObj)
AddSymbol(Sym);
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "Local symtab entries: " << File->getName() << "\n");
for (Symbol *Sym : File->getSymbols())
if (Sym->isLocal())
AddSymbol(Sym);
}
}
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) {
LLVM_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
// 4. The signatures of all imported events
// 5. The signatures of all defined events
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->Signature);
else if (auto *E = dyn_cast<EventSymbol>(Sym))
registerType(*E->Signature);
}
for (const InputFunction *F : InputFunctions)
registerType(F->Signature);
for (const InputEvent *E : InputEvents)
registerType(E->Signature);
}
void Writer::assignIndexes() {
assert(InputFunctions.empty());
uint32_t FunctionIndex = NumImportedFunctions;
auto AddDefinedFunction = [&](InputFunction *Func) {
if (!Func->Live)
return;
InputFunctions.emplace_back(Func);
Func->setFunctionIndex(FunctionIndex++);
};
for (InputFunction *Func : Symtab->SyntheticFunctions)
AddDefinedFunction(Func);
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "Functions: " << File->getName() << "\n");
for (InputFunction *Func : File->Functions)
AddDefinedFunction(Func);
}
uint32_t TableIndex = TableBase;
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_WASM_TABLE_INDEX_I32 ||
Reloc.Type == R_WASM_TABLE_INDEX_SLEB) {
FunctionSymbol *Sym = File->getFunctionSymbol(Reloc.Index);
if (Sym->hasTableIndex() || !Sym->hasFunctionIndex())
continue;
Sym->setTableIndex(TableIndex++);
IndirectFunctions.emplace_back(Sym);
} else if (Reloc.Type == R_WASM_TYPE_INDEX_LEB) {
// Mark target type as live
File->TypeMap[Reloc.Index] = registerType(Types[Reloc.Index]);
File->TypeIsUsed[Reloc.Index] = true;
}
}
};
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "Handle relocs: " << File->getName() << "\n");
for (InputChunk *Chunk : File->Functions)
HandleRelocs(Chunk);
for (InputChunk *Chunk : File->Segments)
HandleRelocs(Chunk);
for (auto &P : File->CustomSections)
HandleRelocs(P);
}
assert(InputGlobals.empty());
uint32_t GlobalIndex = NumImportedGlobals;
auto AddDefinedGlobal = [&](InputGlobal *Global) {
if (Global->Live) {
LLVM_DEBUG(dbgs() << "AddDefinedGlobal: " << GlobalIndex << "\n");
Global->setGlobalIndex(GlobalIndex++);
InputGlobals.push_back(Global);
}
};
for (InputGlobal *Global : Symtab->SyntheticGlobals)
AddDefinedGlobal(Global);
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "Globals: " << File->getName() << "\n");
for (InputGlobal *Global : File->Globals)
AddDefinedGlobal(Global);
}
assert(InputEvents.empty());
uint32_t EventIndex = NumImportedEvents;
auto AddDefinedEvent = [&](InputEvent *Event) {
if (Event->Live) {
LLVM_DEBUG(dbgs() << "AddDefinedEvent: " << EventIndex << "\n");
Event->setEventIndex(EventIndex++);
InputEvents.push_back(Event);
}
};
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "Events: " << File->getName() << "\n");
for (InputEvent *Event : File->Events)
AddDefinedEvent(Event);
}
}
static StringRef getOutputDataSegmentName(StringRef Name) {
// With PIC code we currently only support a single data segment since
// we only have a single __memory_base to use as our base address.
if (Config->Pic)
return "data";
if (!Config->MergeDataSegments)
return Name;
if (Name.startswith(".text."))
return ".text";
if (Name.startswith(".data."))
return ".data";
if (Name.startswith(".bss."))
return ".bss";
if (Name.startswith(".rodata."))
return ".rodata";
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) {
LLVM_DEBUG(dbgs() << "new segment: " << Name << "\n");
S = make<OutputSegment>(Name, Segments.size());
Segments.push_back(S);
}
S->addInputSegment(Segment);
LLVM_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() {
if (!WasmSym::CallCtors->isLive())
return;
// 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->getFunctionIndex(), "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;
}
ArrayRef<uint8_t> Body = arrayRefFromStringRef(Saver.save(FunctionBody));
cast<SyntheticFunction>(WasmSym::CallCtors->Function)->setBody(Body);
}
// 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() {
if (!Config->Relocatable && !WasmSym::CallCtors->isLive())
return;
for (ObjFile *File : Symtab->ObjectFiles) {
const WasmLinkingData &L = File->getWasmObj()->linkingData();
for (const WasmInitFunc &F : L.InitFunctions) {
FunctionSymbol *Sym = File->getFunctionSymbol(F.Symbol);
assert(Sym->isLive());
if (*Sym->Signature != WasmSignature{{}, {}})
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->Pic)
Config->GlobalBase = 0;
// For PIC code the table base is assigned dynamically by the loader.
// For non-PIC, we start at 1 so that accessing table index 0 always traps.
if (!Config->Pic)
TableBase = 1;
log("-- calculateImports");
calculateImports();
log("-- assignIndexes");
assignIndexes();
log("-- calculateInitFunctions");
calculateInitFunctions();
if (!Config->Relocatable)
createCtorFunction();
log("-- calculateTypes");
calculateTypes();
log("-- layoutMemory");
layoutMemory();
log("-- calculateExports");
calculateExports();
log("-- calculateCustomSections");
calculateCustomSections();
log("-- assignSymtab");
assignSymtab();
if (errorHandler().Verbose) {
log("Defined Functions: " + Twine(InputFunctions.size()));
log("Defined Globals : " + Twine(InputGlobals.size()));
log("Defined Events : " + Twine(InputEvents.size()));
log("Function Imports : " + Twine(NumImportedFunctions));
log("Global Imports : " + Twine(NumImportedGlobals));
log("Event Imports : " + Twine(NumImportedEvents));
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(); }
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