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llvm-project/lld/wasm/Writer.cpp

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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 "Relocations.h"
#include "SymbolTable.h"
#include "SyntheticSections.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/SmallSet.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;
namespace {
// The writer writes a SymbolTable result to a file.
class Writer {
public:
void run();
private:
void openFile();
void createApplyRelocationsFunction();
void createCallCtorsFunction();
void assignIndexes();
void populateSymtab();
void populateProducers();
void populateTargetFeatures();
void calculateInitFunctions();
void calculateImports();
void calculateExports();
void calculateCustomSections();
void calculateTypes();
void createOutputSegments();
void layoutMemory();
void createHeader();
void addSection(OutputSection *Sec);
void addSections();
void addStartStopSymbols(const InputSegment *Seg);
void createCustomSections();
void createSyntheticSections();
void finalizeSections();
// Custom sections
void createRelocSections();
void writeHeader();
void writeSections();
uint64_t FileSize = 0;
uint32_t TableBase = 0;
std::vector<WasmInitEntry> InitFunctions;
llvm::StringMap<std::vector<InputSection *>> CustomSectionMapping;
// 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::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 == "target_features" || 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();
LLVM_DEBUG(dbgs() << "createCustomSection: " << Name << "\n");
OutputSection *Sec = make<CustomSection>(Name, Pair.second);
if (Config->Relocatable || Config->EmitRelocs) {
auto *Sym = make<OutputSectionSymbol>(Sec);
Out.LinkingSec->addToSymtab(Sym);
Sec->SectionSym = Sym;
}
addSection(Sec);
}
}
// 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++) {
LLVM_DEBUG(dbgs() << "check section " << I << "\n");
OutputSection *Sec = OutputSections[I];
// Count the number of needed sections.
uint32_t Count = Sec->numRelocations();
if (!Count)
continue;
StringRef Name;
if (Sec->Type == WASM_SEC_DATA)
Name = "reloc.DATA";
else if (Sec->Type == WASM_SEC_CODE)
Name = "reloc.CODE";
else if (Sec->Type == WASM_SEC_CUSTOM)
Name = Saver.save("reloc." + Sec->Name);
else
llvm_unreachable(
"relocations only supported for code, data, or custom sections");
addSection(make<RelocSection>(Name, Sec));
}
}
void Writer::populateProducers() {
for (ObjFile *File : Symtab->ObjectFiles) {
const WasmProducerInfo &Info = File->getWasmObj()->getProducerInfo();
Out.ProducersSec->addInfo(Info);
}
}
void Writer::writeHeader() {
memcpy(Buffer->getBufferStart(), Header.data(), Header.size());
}
void Writer::writeSections() {
uint8_t *Buf = Buffer->getBufferStart();
parallelForEach(OutputSections, [Buf](OutputSection *S) {
assert(S->isNeeded());
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() {
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);
Out.DylinkSec->MemAlign = 0;
for (OutputSegment *Seg : Segments) {
Out.DylinkSec->MemAlign = std::max(Out.DylinkSec->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) {
Out.DylinkSec->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.
log("mem: heap base = " + Twine(MemoryPtr));
if (WasmSym::HeapBase)
WasmSym::HeapBase->setVirtualAddress(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;
}
Out.DylinkSec->MemSize = MemoryPtr;
Out.MemorySec->NumMemoryPages =
alignTo(MemoryPtr, WasmPageSize) / WasmPageSize;
log("mem: total pages = " + Twine(Out.MemorySec->NumMemoryPages));
// Check max if explicitly supplied or required by shared memory
if (Config->MaxMemory != 0 || Config->SharedMemory) {
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");
Out.MemorySec->MaxMemoryPages = Config->MaxMemory / WasmPageSize;
log("mem: max pages = " + Twine(Out.MemorySec->MaxMemoryPages));
}
}
void Writer::addSection(OutputSection *Sec) {
if (!Sec->isNeeded())
return;
log("addSection: " + toString(*Sec));
Sec->SectionIndex = OutputSections.size();
OutputSections.push_back(Sec);
}
// If a section name is valid as a C identifier (which is rare because of
// the leading '.'), linkers are expected to define __start_<secname> and
// __stop_<secname> symbols. They are at beginning and end of the section,
// respectively. This is not requested by the ELF standard, but GNU ld and
// gold provide the feature, and used by many programs.
void Writer::addStartStopSymbols(const InputSegment *Seg) {
StringRef S = Seg->getName();
LLVM_DEBUG(dbgs() << "addStartStopSymbols: " << S << "\n");
if (!isValidCIdentifier(S))
return;
uint32_t Start = Seg->OutputSeg->StartVA + Seg->OutputSegmentOffset;
uint32_t Stop = Start + Seg->getSize();
Symtab->addOptionalDataSymbol(Saver.save("__start_" + S), Start);
Symtab->addOptionalDataSymbol(Saver.save("__stop_" + S), Stop);
}
void Writer::addSections() {
addSection(Out.DylinkSec);
addSection(Out.TypeSec);
addSection(Out.ImportSec);
addSection(Out.FunctionSec);
addSection(Out.TableSec);
addSection(Out.MemorySec);
addSection(Out.GlobalSec);
addSection(Out.EventSec);
addSection(Out.ExportSec);
addSection(Out.ElemSec);
addSection(Out.DataCountSec);
addSection(make<CodeSection>(Out.FunctionSec->InputFunctions));
addSection(make<DataSection>(Segments));
createCustomSections();
addSection(Out.LinkingSec);
if (Config->EmitRelocs || Config->Relocatable) {
createRelocSections();
}
addSection(Out.NameSec);
addSection(Out.ProducersSec);
addSection(Out.TargetFeaturesSec);
}
void Writer::finalizeSections() {
for (OutputSection *S : OutputSections) {
S->setOffset(FileSize);
S->finalizeContents();
FileSize += S->getSize();
}
}
void Writer::populateTargetFeatures() {
StringMap<std::string> Used;
StringMap<std::string> Required;
StringMap<std::string> Disallowed;
// Only infer used features if user did not specify features
bool InferFeatures = !Config->Features.hasValue();
if (!InferFeatures) {
for (auto &Feature : Config->Features.getValue())
Out.TargetFeaturesSec->Features.insert(Feature);
// No need to read or check features
if (!Config->CheckFeatures)
return;
}
// Find the sets of used, required, and disallowed features
for (ObjFile *File : Symtab->ObjectFiles) {
StringRef FileName(File->getName());
for (auto &Feature : File->getWasmObj()->getTargetFeatures()) {
switch (Feature.Prefix) {
case WASM_FEATURE_PREFIX_USED:
Used.insert({Feature.Name, FileName});
break;
case WASM_FEATURE_PREFIX_REQUIRED:
Used.insert({Feature.Name, FileName});
Required.insert({Feature.Name, FileName});
break;
case WASM_FEATURE_PREFIX_DISALLOWED:
Disallowed.insert({Feature.Name, FileName});
break;
default:
error("Unrecognized feature policy prefix " +
std::to_string(Feature.Prefix));
}
}
}
if (InferFeatures)
Out.TargetFeaturesSec->Features.insert(Used.keys().begin(),
Used.keys().end());
if (Out.TargetFeaturesSec->Features.count("atomics") &&
!Config->SharedMemory) {
if (InferFeatures)
error(Twine("'atomics' feature is used by ") + Used["atomics"] +
", so --shared-memory must be used");
else
error("'atomics' feature is used, so --shared-memory must be used");
}
if (!Config->CheckFeatures)
return;
if (Disallowed.count("atomics") && Config->SharedMemory)
error("'atomics' feature is disallowed by " + Disallowed["atomics"] +
", so --shared-memory must not be used");
// Validate that used features are allowed in output
if (!InferFeatures) {
for (auto &Feature : Used.keys()) {
if (!Out.TargetFeaturesSec->Features.count(Feature))
error(Twine("Target feature '") + Feature + "' used by " +
Used[Feature] + " is not allowed.");
}
}
// Validate the required and disallowed constraints for each file
for (ObjFile *File : Symtab->ObjectFiles) {
StringRef FileName(File->getName());
SmallSet<std::string, 8> ObjectFeatures;
for (auto &Feature : File->getWasmObj()->getTargetFeatures()) {
if (Feature.Prefix == WASM_FEATURE_PREFIX_DISALLOWED)
continue;
ObjectFeatures.insert(Feature.Name);
if (Disallowed.count(Feature.Name))
error(Twine("Target feature '") + Feature.Name + "' used in " +
FileName + " is disallowed by " + Disallowed[Feature.Name] +
". Use --no-check-features to suppress.");
}
for (auto &Feature : Required.keys()) {
if (!ObjectFeatures.count(Feature))
error(Twine("Missing target feature '") + Feature + "' in " + FileName +
", required by " + Required[Feature] +
". Use --no-check-features to suppress.");
}
}
}
void Writer::calculateImports() {
for (Symbol *Sym : Symtab->getSymbols()) {
if (!Sym->isUndefined())
continue;
if (Sym->isWeak() && !Config->Relocatable)
continue;
if (!Sym->isLive())
continue;
if (!Sym->IsUsedInRegularObj)
continue;
// We don't generate imports for data symbols. They however can be imported
// as GOT entries.
if (isa<DataSymbol>(Sym))
continue;
LLVM_DEBUG(dbgs() << "import: " << Sym->getName() << "\n");
Out.ImportSec->addImport(Sym);
}
}
void Writer::calculateExports() {
if (Config->Relocatable)
return;
if (!Config->Relocatable && !Config->ImportMemory)
Out.ExportSec->Exports.push_back(
WasmExport{"memory", WASM_EXTERNAL_MEMORY, 0});
if (!Config->Relocatable && Config->ExportTable)
Out.ExportSec->Exports.push_back(
WasmExport{FunctionTableName, WASM_EXTERNAL_TABLE, 0});
unsigned FakeGlobalIndex =
Out.ImportSec->numImportedGlobals() + Out.GlobalSec->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);
Out.GlobalSec->DefinedFakeGlobals.emplace_back(D);
Export = {Name, WASM_EXTERNAL_GLOBAL, FakeGlobalIndex++};
}
LLVM_DEBUG(dbgs() << "Export: " << Name << "\n");
Out.ExportSec->Exports.push_back(Export);
}
}
void Writer::populateSymtab() {
if (!Config->Relocatable && !Config->EmitRelocs)
return;
for (Symbol *Sym : Symtab->getSymbols())
if (Sym->IsUsedInRegularObj && Sym->isLive())
Out.LinkingSec->addToSymtab(Sym);
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "Local symtab entries: " << File->getName() << "\n");
for (Symbol *Sym : File->getSymbols())
if (Sym->isLocal() && !isa<SectionSymbol>(Sym) && Sym->isLive())
Out.LinkingSec->addToSymtab(Sym);
}
}
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] = Out.TypeSec->registerType(Types[I]);
}
for (const Symbol *Sym : Out.ImportSec->ImportedSymbols) {
if (auto *F = dyn_cast<FunctionSymbol>(Sym))
Out.TypeSec->registerType(*F->Signature);
else if (auto *E = dyn_cast<EventSymbol>(Sym))
Out.TypeSec->registerType(*E->Signature);
}
for (const InputFunction *F : Out.FunctionSec->InputFunctions)
Out.TypeSec->registerType(F->Signature);
for (const InputEvent *E : Out.EventSec->InputEvents)
Out.TypeSec->registerType(E->Signature);
}
static void scanRelocations() {
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "scanRelocations: " << File->getName() << "\n");
for (InputChunk *Chunk : File->Functions)
scanRelocations(Chunk);
for (InputChunk *Chunk : File->Segments)
scanRelocations(Chunk);
for (auto &P : File->CustomSections)
scanRelocations(P);
}
}
void Writer::assignIndexes() {
// Seal the import section, since other index spaces such as function and
// global are effected by the number of imports.
Out.ImportSec->seal();
for (InputFunction *Func : Symtab->SyntheticFunctions)
Out.FunctionSec->addFunction(Func);
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "Functions: " << File->getName() << "\n");
for (InputFunction *Func : File->Functions)
Out.FunctionSec->addFunction(Func);
}
for (InputGlobal *Global : Symtab->SyntheticGlobals)
Out.GlobalSec->addGlobal(Global);
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "Globals: " << File->getName() << "\n");
for (InputGlobal *Global : File->Globals)
Out.GlobalSec->addGlobal(Global);
}
for (ObjFile *File : Symtab->ObjectFiles) {
LLVM_DEBUG(dbgs() << "Events: " << File->getName() << "\n");
for (InputEvent *Event : File->Events)
Out.EventSec->addEvent(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");
}
}
}
// For -shared (PIC) output, we create create a synthetic function which will
// apply any relocations to the data segments on startup. This function is
// called __wasm_apply_relocs and is added at the very beginning of
// __wasm_call_ctors before any of the constructors run.
void Writer::createApplyRelocationsFunction() {
LLVM_DEBUG(dbgs() << "createApplyRelocationsFunction\n");
// First write the body's contents to a string.
std::string BodyContent;
{
raw_string_ostream OS(BodyContent);
writeUleb128(OS, 0, "num locals");
for (const OutputSegment *Seg : Segments)
for (const InputSegment *InSeg : Seg->InputSegments)
InSeg->generateRelocationCode(OS);
writeU8(OS, WASM_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::ApplyRelocs->Function)->setBody(Body);
}
// Create synthetic "__wasm_call_ctors" function based on ctor functions
// in input object.
void Writer::createCallCtorsFunction() {
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");
if (Config->Pic) {
writeU8(OS, WASM_OPCODE_CALL, "CALL");
writeUleb128(OS, WasmSym::ApplyRelocs->getFunctionIndex(),
"function index");
}
for (const WasmInitEntry &F : InitFunctions) {
writeU8(OS, WASM_OPCODE_CALL, "CALL");
writeUleb128(OS, F.Sym->getFunctionIndex(), "function index");
}
writeU8(OS, WASM_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);
// comdat exclusions can cause init functions be discarded.
if (Sym->isDiscarded())
continue;
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.
llvm::stable_sort(InitFunctions,
[](const WasmInitEntry &L, const WasmInitEntry &R) {
return L.Priority < R.Priority;
});
}
void Writer::createSyntheticSections() {
Out.DylinkSec = make<DylinkSection>();
Out.TypeSec = make<TypeSection>();
Out.ImportSec = make<ImportSection>();
Out.FunctionSec = make<FunctionSection>();
Out.TableSec = make<TableSection>();
Out.MemorySec = make<MemorySection>();
Out.GlobalSec = make<GlobalSection>();
Out.EventSec = make<EventSection>();
Out.ExportSec = make<ExportSection>();
Out.ElemSec = make<ElemSection>(TableBase);
Out.DataCountSec = make<DataCountSection>(Segments.size());
Out.LinkingSec = make<LinkingSection>(InitFunctions, Segments);
Out.NameSec = make<NameSection>();
Out.ProducersSec = make<ProducersSection>();
Out.TargetFeaturesSec = make<TargetFeaturesSection>();
}
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("-- createOutputSegments");
createOutputSegments();
log("-- createSyntheticSections");
createSyntheticSections();
log("-- populateProducers");
populateProducers();
log("-- populateTargetFeatures");
populateTargetFeatures();
log("-- calculateImports");
calculateImports();
log("-- layoutMemory");
layoutMemory();
if (!Config->Relocatable) {
// Create linker synthesized __start_SECNAME/__stop_SECNAME symbols
// This has to be done after memory layout is performed.
for (const OutputSegment *Seg : Segments)
for (const InputSegment *S : Seg->InputSegments)
addStartStopSymbols(S);
}
log("-- scanRelocations");
scanRelocations();
log("-- assignIndexes");
assignIndexes();
log("-- calculateInitFunctions");
calculateInitFunctions();
if (!Config->Relocatable) {
// Create linker synthesized functions
if (Config->Pic)
createApplyRelocationsFunction();
createCallCtorsFunction();
// Make sure we have resolved all symbols.
if (!Config->AllowUndefined)
Symtab->reportRemainingUndefines();
if (errorCount())
return;
}
log("-- calculateTypes");
calculateTypes();
log("-- calculateExports");
calculateExports();
log("-- calculateCustomSections");
calculateCustomSections();
log("-- populateSymtab");
populateSymtab();
log("-- addSections");
addSections();
if (errorHandler().Verbose) {
log("Defined Functions: " + Twine(Out.FunctionSec->InputFunctions.size()));
log("Defined Globals : " + Twine(Out.GlobalSec->InputGlobals.size()));
log("Defined Events : " + Twine(Out.EventSec->InputEvents.size()));
log("Function Imports : " + Twine(Out.ImportSec->numImportedFunctions()));
log("Global Imports : " + Twine(Out.ImportSec->numImportedGlobals()));
log("Event Imports : " + Twine(Out.ImportSec->numImportedEvents()));
for (ObjFile *File : Symtab->ObjectFiles)
File->dumpInfo();
}
createHeader();
log("-- finalizeSections");
finalizeSections();
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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