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llvm-project/lld/wasm/Writer.cpp
Kazu Hirata 00cb966209
[lld] Use *Set::insert_range (NFC) (#132590) 
DenseSet, SmallPtrSet, SmallSet, SetVector, and StringSet recently
gained C++23-style insert_range.  This patch replaces:

  Dest.insert(Src.begin(), Src.end());

with:

  Dest.insert_range(Src);
2025-03-22 21:57:06 -07:00

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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 "InputElement.h"
#include "MapFile.h"
#include "OutputSections.h"
#include "OutputSegment.h"
#include "Relocations.h"
#include "SymbolTable.h"
#include "SyntheticSections.h"
#include "WriterUtils.h"
#include "lld/Common/Arrays.h"
#include "lld/Common/CommonLinkerContext.h"
#include "lld/Common/Strings.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/BinaryFormat/Wasm.h"
#include "llvm/BinaryFormat/WasmTraits.h"
#include "llvm/Support/FileOutputBuffer.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/Parallel.h"
#include "llvm/Support/RandomNumberGenerator.h"
#include "llvm/Support/SHA1.h"
#include "llvm/Support/xxhash.h"
#include <cstdarg>
#include <map>
#include <optional>
#define DEBUG_TYPE "lld"
using namespace llvm;
using namespace llvm::wasm;
namespace lld::wasm {
static constexpr int stackAlignment = 16;
static constexpr int heapAlignment = 16;
namespace {
// The writer writes a SymbolTable result to a file.
class Writer {
public:
void run();
private:
void openFile();
bool needsPassiveInitialization(const OutputSegment *segment);
bool hasPassiveInitializedSegments();
void createSyntheticInitFunctions();
void createInitMemoryFunction();
void createStartFunction();
void createApplyDataRelocationsFunction();
void createApplyGlobalRelocationsFunction();
void createApplyTLSRelocationsFunction();
void createApplyGlobalTLSRelocationsFunction();
void createCallCtorsFunction();
void createInitTLSFunction();
void createCommandExportWrappers();
void createCommandExportWrapper(uint32_t functionIndex, DefinedFunction *f);
void assignIndexes();
void populateSymtab();
void populateProducers();
void populateTargetFeatures();
// populateTargetFeatures happens early on so some checks are delayed
// until imports and exports are finalized. There are run unstead
// in checkImportExportTargetFeatures
void checkImportExportTargetFeatures();
void calculateInitFunctions();
void calculateImports();
void calculateExports();
void calculateCustomSections();
void calculateTypes();
void createOutputSegments();
OutputSegment *createOutputSegment(StringRef name);
void combineOutputSegments();
void layoutMemory();
void createHeader();
void addSection(OutputSection *sec);
void addSections();
void createCustomSections();
void createSyntheticSections();
void createSyntheticSectionsPostLayout();
void finalizeSections();
// Custom sections
void createRelocSections();
void writeHeader();
void writeSections();
void writeBuildId();
uint64_t fileSize = 0;
std::vector<WasmInitEntry> initFunctions;
llvm::MapVector<StringRef, std::vector<InputChunk *>> customSectionMapping;
// Stable storage for command export wrapper function name strings.
std::list<std::string> commandExportWrapperNames;
// 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 = ctx.arg.stripDebug || ctx.arg.stripAll;
for (ObjFile *file : ctx.objectFiles) {
for (InputChunk *section : file->customSections) {
// Exclude COMDAT sections that are not selected for inclusion
if (section->discarded)
continue;
// Ignore empty custom sections. In particular objcopy/strip will
// sometimes replace stripped sections with empty custom sections to
// avoid section re-numbering.
if (section->getSize() == 0)
continue;
StringRef name = section->name;
// These custom sections are known the linker and synthesized rather than
// blindly copied.
if (name == "linking" || name == "name" || name == "producers" ||
name == "target_features" || name.starts_with("reloc."))
continue;
// These custom sections are generated by `clang -fembed-bitcode`.
// These are used by the rust toolchain to ship LTO data along with
// compiled object code, but they don't want this included in the linker
// output.
if (name == ".llvmbc" || name == ".llvmcmd")
continue;
// Strip debug section in that option was specified.
if (stripDebug && name.starts_with(".debug_"))
continue;
// Otherwise include custom sections by default and concatenate their
// contents.
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>(std::string(name), pair.second);
if (ctx.arg.relocatable || ctx.arg.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->getNumRelocations();
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 : ctx.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);
});
}
// Computes a hash value of Data using a given hash function.
// In order to utilize multiple cores, we first split data into 1MB
// chunks, compute a hash for each chunk, and then compute a hash value
// of the hash values.
static void
computeHash(llvm::MutableArrayRef<uint8_t> hashBuf,
llvm::ArrayRef<uint8_t> data,
std::function<void(uint8_t *dest, ArrayRef<uint8_t> arr)> hashFn) {
std::vector<ArrayRef<uint8_t>> chunks = split(data, 1024 * 1024);
std::vector<uint8_t> hashes(chunks.size() * hashBuf.size());
// Compute hash values.
parallelFor(0, chunks.size(), [&](size_t i) {
hashFn(hashes.data() + i * hashBuf.size(), chunks[i]);
});
// Write to the final output buffer.
hashFn(hashBuf.data(), hashes);
}
static void makeUUID(unsigned version, llvm::ArrayRef<uint8_t> fileHash,
llvm::MutableArrayRef<uint8_t> output) {
assert((version == 4 || version == 5) && "Unknown UUID version");
assert(output.size() == 16 && "Wrong size for UUID output");
if (version == 5) {
// Build a valid v5 UUID from a hardcoded (randomly-generated) namespace
// UUID, and the computed hash of the output.
std::array<uint8_t, 16> namespaceUUID{0xA1, 0xFA, 0x48, 0x2D, 0x0E, 0x22,
0x03, 0x8D, 0x33, 0x8B, 0x52, 0x1C,
0xD6, 0xD2, 0x12, 0xB2};
SHA1 sha;
sha.update(namespaceUUID);
sha.update(fileHash);
auto s = sha.final();
std::copy(s.data(), &s.data()[output.size()], output.data());
} else if (version == 4) {
if (auto ec = llvm::getRandomBytes(output.data(), output.size()))
error("entropy source failure: " + ec.message());
}
// Set the UUID version and variant fields.
// The version is the upper nibble of byte 6 (0b0101xxxx or 0b0100xxxx)
output[6] = (static_cast<uint8_t>(version) << 4) | (output[6] & 0xF);
// The variant is DCE 1.1/ISO 11578 (0b10xxxxxx)
output[8] &= 0xBF;
output[8] |= 0x80;
}
void Writer::writeBuildId() {
if (!out.buildIdSec->isNeeded())
return;
if (ctx.arg.buildId == BuildIdKind::Hexstring) {
out.buildIdSec->writeBuildId(ctx.arg.buildIdVector);
return;
}
// Compute a hash of all sections of the output file.
size_t hashSize = out.buildIdSec->hashSize;
std::vector<uint8_t> buildId(hashSize);
llvm::ArrayRef<uint8_t> buf{buffer->getBufferStart(), size_t(fileSize)};
switch (ctx.arg.buildId) {
case BuildIdKind::Fast: {
std::vector<uint8_t> fileHash(8);
computeHash(fileHash, buf, [](uint8_t *dest, ArrayRef<uint8_t> arr) {
support::endian::write64le(dest, xxh3_64bits(arr));
});
makeUUID(5, fileHash, buildId);
break;
}
case BuildIdKind::Sha1:
computeHash(buildId, buf, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
memcpy(dest, SHA1::hash(arr).data(), hashSize);
});
break;
case BuildIdKind::Uuid:
makeUUID(4, {}, buildId);
break;
default:
llvm_unreachable("unknown BuildIdKind");
}
out.buildIdSec->writeBuildId(buildId);
}
static void setGlobalPtr(DefinedGlobal *g, uint64_t memoryPtr) {
LLVM_DEBUG(dbgs() << "setGlobalPtr " << g->getName() << " -> " << memoryPtr << "\n");
g->global->setPointerValue(memoryPtr);
}
static void checkPageAligned(StringRef name, uint64_t value) {
if (value != alignTo(value, ctx.arg.pageSize))
error(name + " must be aligned to the page size (" +
Twine(ctx.arg.pageSize) + " bytes)");
}
// 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 ctx.arg.globalBase)
// - BSS data (not currently implemented in llvm)
// - explicit stack (ctx.arg.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() {
uint64_t memoryPtr = 0;
auto placeStack = [&]() {
if (ctx.arg.relocatable || ctx.isPic)
return;
memoryPtr = alignTo(memoryPtr, stackAlignment);
if (WasmSym::stackLow)
WasmSym::stackLow->setVA(memoryPtr);
if (ctx.arg.zStackSize != alignTo(ctx.arg.zStackSize, stackAlignment))
error("stack size must be " + Twine(stackAlignment) + "-byte aligned");
log("mem: stack size = " + Twine(ctx.arg.zStackSize));
log("mem: stack base = " + Twine(memoryPtr));
memoryPtr += ctx.arg.zStackSize;
setGlobalPtr(cast<DefinedGlobal>(WasmSym::stackPointer), memoryPtr);
if (WasmSym::stackHigh)
WasmSym::stackHigh->setVA(memoryPtr);
log("mem: stack top = " + Twine(memoryPtr));
};
if (ctx.arg.stackFirst) {
placeStack();
if (ctx.arg.globalBase) {
if (ctx.arg.globalBase < memoryPtr) {
error("--global-base cannot be less than stack size when --stack-first is used");
return;
}
memoryPtr = ctx.arg.globalBase;
}
} else {
memoryPtr = ctx.arg.globalBase;
}
log("mem: global base = " + Twine(memoryPtr));
if (WasmSym::globalBase)
WasmSym::globalBase->setVA(memoryPtr);
uint64_t dataStart = memoryPtr;
// Arbitrarily set __dso_handle handle to point to the start of the data
// segments.
if (WasmSym::dsoHandle)
WasmSym::dsoHandle->setVA(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));
if (!ctx.arg.relocatable && seg->isTLS()) {
if (WasmSym::tlsSize) {
auto *tlsSize = cast<DefinedGlobal>(WasmSym::tlsSize);
setGlobalPtr(tlsSize, seg->size);
}
if (WasmSym::tlsAlign) {
auto *tlsAlign = cast<DefinedGlobal>(WasmSym::tlsAlign);
setGlobalPtr(tlsAlign, int64_t{1} << seg->alignment);
}
if (!ctx.arg.sharedMemory && WasmSym::tlsBase) {
auto *tlsBase = cast<DefinedGlobal>(WasmSym::tlsBase);
setGlobalPtr(tlsBase, memoryPtr);
}
}
memoryPtr += seg->size;
}
// Make space for the memory initialization flag
if (ctx.arg.sharedMemory && hasPassiveInitializedSegments()) {
memoryPtr = alignTo(memoryPtr, 4);
WasmSym::initMemoryFlag = symtab->addSyntheticDataSymbol(
"__wasm_init_memory_flag", WASM_SYMBOL_VISIBILITY_HIDDEN);
WasmSym::initMemoryFlag->markLive();
WasmSym::initMemoryFlag->setVA(memoryPtr);
log(formatv("mem: {0,-15} offset={1,-8} size={2,-8} align={3}",
"__wasm_init_memory_flag", memoryPtr, 4, 4));
memoryPtr += 4;
}
if (WasmSym::dataEnd)
WasmSym::dataEnd->setVA(memoryPtr);
uint64_t staticDataSize = memoryPtr - dataStart;
log("mem: static data = " + Twine(staticDataSize));
if (ctx.isPic)
out.dylinkSec->memSize = staticDataSize;
if (!ctx.arg.stackFirst)
placeStack();
if (WasmSym::heapBase) {
// Set `__heap_base` to 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.
// We'll align the heap base here because memory allocators might expect
// __heap_base to be aligned already.
memoryPtr = alignTo(memoryPtr, heapAlignment);
log("mem: heap base = " + Twine(memoryPtr));
WasmSym::heapBase->setVA(memoryPtr);
}
uint64_t maxMemorySetting = 1ULL << 32;
if (ctx.arg.is64.value_or(false)) {
// TODO: Update once we decide on a reasonable limit here:
// https://github.com/WebAssembly/memory64/issues/33
maxMemorySetting = 1ULL << 34;
}
if (ctx.arg.initialHeap != 0) {
checkPageAligned("initial heap", ctx.arg.initialHeap);
uint64_t maxInitialHeap = maxMemorySetting - memoryPtr;
if (ctx.arg.initialHeap > maxInitialHeap)
error("initial heap too large, cannot be greater than " +
Twine(maxInitialHeap));
memoryPtr += ctx.arg.initialHeap;
}
if (ctx.arg.initialMemory != 0) {
checkPageAligned("initial memory", ctx.arg.initialMemory);
if (memoryPtr > ctx.arg.initialMemory)
error("initial memory too small, " + Twine(memoryPtr) + " bytes needed");
if (ctx.arg.initialMemory > maxMemorySetting)
error("initial memory too large, cannot be greater than " +
Twine(maxMemorySetting));
memoryPtr = ctx.arg.initialMemory;
}
memoryPtr = alignTo(memoryPtr, ctx.arg.pageSize);
out.memorySec->numMemoryPages = memoryPtr / ctx.arg.pageSize;
log("mem: total pages = " + Twine(out.memorySec->numMemoryPages));
if (WasmSym::heapEnd) {
// Set `__heap_end` to follow the end of the statically allocated linear
// memory. The fact that this comes last means that a malloc/brk
// implementation can grow the heap at runtime.
log("mem: heap end = " + Twine(memoryPtr));
WasmSym::heapEnd->setVA(memoryPtr);
}
uint64_t maxMemory = 0;
if (ctx.arg.maxMemory != 0) {
checkPageAligned("maximum memory", ctx.arg.maxMemory);
if (memoryPtr > ctx.arg.maxMemory)
error("maximum memory too small, " + Twine(memoryPtr) + " bytes needed");
if (ctx.arg.maxMemory > maxMemorySetting)
error("maximum memory too large, cannot be greater than " +
Twine(maxMemorySetting));
maxMemory = ctx.arg.maxMemory;
} else if (ctx.arg.noGrowableMemory) {
maxMemory = memoryPtr;
}
// If no maxMemory config was supplied but we are building with
// shared memory, we need to pick a sensible upper limit.
if (ctx.arg.sharedMemory && maxMemory == 0) {
if (ctx.isPic)
maxMemory = maxMemorySetting;
else
maxMemory = memoryPtr;
}
if (maxMemory != 0) {
out.memorySec->maxMemoryPages = maxMemory / ctx.arg.pageSize;
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.
static void addStartStopSymbols(const OutputSegment *seg) {
StringRef name = seg->name;
if (!isValidCIdentifier(name))
return;
LLVM_DEBUG(dbgs() << "addStartStopSymbols: " << name << "\n");
uint64_t start = seg->startVA;
uint64_t stop = start + seg->size;
symtab->addOptionalDataSymbol(saver().save("__start_" + name), start);
symtab->addOptionalDataSymbol(saver().save("__stop_" + name), stop);
}
void Writer::addSections() {
addSection(out.dylinkSec);
addSection(out.typeSec);
addSection(out.importSec);
addSection(out.functionSec);
addSection(out.tableSec);
addSection(out.memorySec);
addSection(out.tagSec);
addSection(out.globalSec);
addSection(out.exportSec);
addSection(out.startSec);
addSection(out.elemSec);
addSection(out.dataCountSec);
addSection(make<CodeSection>(out.functionSec->inputFunctions));
addSection(make<DataSection>(segments));
createCustomSections();
addSection(out.linkingSec);
if (ctx.arg.emitRelocs || ctx.arg.relocatable) {
createRelocSections();
}
addSection(out.nameSec);
addSection(out.producersSec);
addSection(out.targetFeaturesSec);
addSection(out.buildIdSec);
}
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> disallowed;
SmallSet<std::string, 8> &allowed = out.targetFeaturesSec->features;
bool tlsUsed = false;
if (ctx.isPic) {
// This should not be necessary because all PIC objects should
// contain the mutable-globals feature.
// TODO (https://github.com/llvm/llvm-project/issues/51681)
allowed.insert("mutable-globals");
}
if (ctx.arg.extraFeatures.has_value()) {
auto &extraFeatures = *ctx.arg.extraFeatures;
allowed.insert_range(extraFeatures);
}
// Only infer used features if user did not specify features
bool inferFeatures = !ctx.arg.features.has_value();
if (!inferFeatures) {
auto &explicitFeatures = *ctx.arg.features;
allowed.insert_range(explicitFeatures);
if (!ctx.arg.checkFeatures)
goto done;
}
// Find the sets of used and disallowed features
for (ObjFile *file : ctx.objectFiles) {
StringRef fileName(file->getName());
for (auto &feature : file->getWasmObj()->getTargetFeatures()) {
switch (feature.Prefix) {
case WASM_FEATURE_PREFIX_USED:
used.insert({feature.Name, std::string(fileName)});
break;
case WASM_FEATURE_PREFIX_DISALLOWED:
disallowed.insert({feature.Name, std::string(fileName)});
break;
default:
error("Unrecognized feature policy prefix " +
std::to_string(feature.Prefix));
}
}
// Find TLS data segments
auto isTLS = [](InputChunk *segment) {
return segment->live && segment->isTLS();
};
tlsUsed = tlsUsed || llvm::any_of(file->segments, isTLS);
}
if (inferFeatures)
for (const auto &key : used.keys())
allowed.insert(std::string(key));
if (!ctx.arg.checkFeatures)
goto done;
if (ctx.arg.sharedMemory) {
if (disallowed.count("shared-mem"))
error("--shared-memory is disallowed by " + disallowed["shared-mem"] +
" because it was not compiled with 'atomics' or 'bulk-memory' "
"features.");
for (auto feature : {"atomics", "bulk-memory"})
if (!allowed.count(feature))
error(StringRef("'") + feature +
"' feature must be used in order to use shared memory");
}
if (tlsUsed) {
for (auto feature : {"atomics", "bulk-memory"})
if (!allowed.count(feature))
error(StringRef("'") + feature +
"' feature must be used in order to use thread-local storage");
}
// Validate that used features are allowed in output
if (!inferFeatures) {
for (const auto &feature : used.keys()) {
if (!allowed.count(std::string(feature)))
error(Twine("Target feature '") + feature + "' used by " +
used[feature] + " is not allowed.");
}
}
// Validate the disallowed constraints for each file
for (ObjFile *file : ctx.objectFiles) {
StringRef fileName(file->getName());
SmallSet<std::string, 8> objectFeatures;
for (const 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.");
}
}
done:
// Normally we don't include bss segments in the binary. In particular if
// memory is not being imported then we can assume its zero initialized.
// In the case the memory is imported, and we can use the memory.fill
// instruction, then we can also avoid including the segments.
// Finally, if we are emitting relocations, they may refer to locations within
// the bss segments, so these segments need to exist in the binary.
if (ctx.arg.emitRelocs ||
(ctx.arg.memoryImport.has_value() && !allowed.count("bulk-memory")))
ctx.emitBssSegments = true;
if (allowed.count("extended-const"))
ctx.arg.extendedConst = true;
for (auto &feature : allowed)
log("Allowed feature: " + feature);
}
void Writer::checkImportExportTargetFeatures() {
if (ctx.arg.relocatable || !ctx.arg.checkFeatures)
return;
if (out.targetFeaturesSec->features.count("mutable-globals") == 0) {
for (const Symbol *sym : out.importSec->importedSymbols) {
if (auto *global = dyn_cast<GlobalSymbol>(sym)) {
if (global->getGlobalType()->Mutable) {
error(Twine("mutable global imported but 'mutable-globals' feature "
"not present in inputs: `") +
toString(*sym) + "`. Use --no-check-features to suppress.");
}
}
}
for (const Symbol *sym : out.exportSec->exportedSymbols) {
if (isa<GlobalSymbol>(sym)) {
error(Twine("mutable global exported but 'mutable-globals' feature "
"not present in inputs: `") +
toString(*sym) + "`. Use --no-check-features to suppress.");
}
}
}
}
static bool shouldImport(Symbol *sym) {
// We don't generate imports for data symbols. They however can be imported
// as GOT entries.
if (isa<DataSymbol>(sym))
return false;
if (!sym->isLive())
return false;
if (!sym->isUsedInRegularObj)
return false;
// When a symbol is weakly defined in a shared library we need to allow
// it to be overridden by another module so need to both import
// and export the symbol.
if (ctx.arg.shared && sym->isWeak() && !sym->isUndefined() &&
!sym->isHidden())
return true;
if (sym->isShared())
return true;
if (!sym->isUndefined())
return false;
if (sym->isWeak() && !ctx.arg.relocatable && !ctx.isPic)
return false;
// In PIC mode we only need to import functions when they are called directly.
// Indirect usage all goes via GOT imports.
if (ctx.isPic) {
if (auto *f = dyn_cast<UndefinedFunction>(sym))
if (!f->isCalledDirectly)
return false;
}
if (ctx.isPic || ctx.arg.relocatable || ctx.arg.importUndefined ||
ctx.arg.unresolvedSymbols == UnresolvedPolicy::ImportDynamic)
return true;
if (ctx.arg.allowUndefinedSymbols.count(sym->getName()) != 0)
return true;
return sym->isImported();
}
void Writer::calculateImports() {
// Some inputs require that the indirect function table be assigned to table
// number 0, so if it is present and is an import, allocate it before any
// other tables.
if (WasmSym::indirectFunctionTable &&
shouldImport(WasmSym::indirectFunctionTable))
out.importSec->addImport(WasmSym::indirectFunctionTable);
for (Symbol *sym : symtab->symbols()) {
if (!shouldImport(sym))
continue;
if (sym == WasmSym::indirectFunctionTable)
continue;
LLVM_DEBUG(dbgs() << "import: " << sym->getName() << "\n");
out.importSec->addImport(sym);
}
}
void Writer::calculateExports() {
if (ctx.arg.relocatable)
return;
if (!ctx.arg.relocatable && ctx.arg.memoryExport.has_value()) {
out.exportSec->exports.push_back(
WasmExport{*ctx.arg.memoryExport, WASM_EXTERNAL_MEMORY, 0});
}
unsigned globalIndex =
out.importSec->getNumImportedGlobals() + out.globalSec->numGlobals();
for (Symbol *sym : symtab->symbols()) {
if (!sym->isExported())
continue;
if (!sym->isLive())
continue;
if (isa<SharedFunctionSymbol>(sym) || sym->isShared())
continue;
StringRef name = sym->getName();
LLVM_DEBUG(dbgs() << "Export: " << name << "\n");
WasmExport export_;
if (auto *f = dyn_cast<DefinedFunction>(sym)) {
if (std::optional<StringRef> exportName = f->function->getExportName()) {
name = *exportName;
}
export_ = {name, WASM_EXTERNAL_FUNCTION, f->getExportedFunctionIndex()};
} else if (auto *g = dyn_cast<DefinedGlobal>(sym)) {
if (g->getGlobalType()->Mutable && !g->getFile() && !g->forceExport) {
// Avoid exporting mutable globals are linker synthesized (e.g.
// __stack_pointer or __tls_base) unless they are explicitly exported
// from the command line.
// Without this check `--export-all` would cause any program using the
// stack pointer to export a mutable global even if none of the input
// files were built with the `mutable-globals` feature.
continue;
}
export_ = {name, WASM_EXTERNAL_GLOBAL, g->getGlobalIndex()};
} else if (auto *t = dyn_cast<DefinedTag>(sym)) {
export_ = {name, WASM_EXTERNAL_TAG, t->getTagIndex()};
} else if (auto *d = dyn_cast<DefinedData>(sym)) {
out.globalSec->dataAddressGlobals.push_back(d);
export_ = {name, WASM_EXTERNAL_GLOBAL, globalIndex++};
} else {
auto *t = cast<DefinedTable>(sym);
export_ = {name, WASM_EXTERNAL_TABLE, t->getTableNumber()};
}
out.exportSec->exports.push_back(export_);
out.exportSec->exportedSymbols.push_back(sym);
}
}
void Writer::populateSymtab() {
if (!ctx.arg.relocatable && !ctx.arg.emitRelocs)
return;
for (Symbol *sym : symtab->symbols())
if (sym->isUsedInRegularObj && sym->isLive() && !sym->isShared())
out.linkingSec->addToSymtab(sym);
for (ObjFile *file : ctx.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 tags
// 5. The signatures of all defined tags
for (ObjFile *file : ctx.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 *t = dyn_cast<TagSymbol>(sym))
out.typeSec->registerType(*t->signature);
}
for (const InputFunction *f : out.functionSec->inputFunctions)
out.typeSec->registerType(f->signature);
for (const InputTag *t : out.tagSec->inputTags)
out.typeSec->registerType(t->signature);
}
// In a command-style link, create a wrapper for each exported symbol
// which calls the constructors and destructors.
void Writer::createCommandExportWrappers() {
// This logic doesn't currently support Emscripten-style PIC mode.
assert(!ctx.isPic);
// If there are no ctors and there's no libc `__wasm_call_dtors` to
// call, don't wrap the exports.
if (initFunctions.empty() && WasmSym::callDtors == nullptr)
return;
std::vector<DefinedFunction *> toWrap;
for (Symbol *sym : symtab->symbols())
if (sym->isExported())
if (auto *f = dyn_cast<DefinedFunction>(sym))
toWrap.push_back(f);
for (auto *f : toWrap) {
auto funcNameStr = (f->getName() + ".command_export").str();
commandExportWrapperNames.push_back(funcNameStr);
const std::string &funcName = commandExportWrapperNames.back();
auto func = make<SyntheticFunction>(*f->getSignature(), funcName);
if (f->function->getExportName())
func->setExportName(f->function->getExportName()->str());
else
func->setExportName(f->getName().str());
DefinedFunction *def =
symtab->addSyntheticFunction(funcName, f->flags, func);
def->markLive();
def->flags |= WASM_SYMBOL_EXPORTED;
def->flags &= ~WASM_SYMBOL_VISIBILITY_HIDDEN;
def->forceExport = f->forceExport;
f->flags |= WASM_SYMBOL_VISIBILITY_HIDDEN;
f->flags &= ~WASM_SYMBOL_EXPORTED;
f->forceExport = false;
out.functionSec->addFunction(func);
createCommandExportWrapper(f->getFunctionIndex(), def);
}
}
static void finalizeIndirectFunctionTable() {
if (!WasmSym::indirectFunctionTable)
return;
if (shouldImport(WasmSym::indirectFunctionTable) &&
!WasmSym::indirectFunctionTable->hasTableNumber()) {
// Processing -Bsymbolic relocations resulted in a late requirement that the
// indirect function table be present, and we are running in --import-table
// mode. Add the table now to the imports section. Otherwise it will be
// added to the tables section later in assignIndexes.
out.importSec->addImport(WasmSym::indirectFunctionTable);
}
uint32_t tableSize = ctx.arg.tableBase + out.elemSec->numEntries();
WasmLimits limits = {0, tableSize, 0, 0};
if (WasmSym::indirectFunctionTable->isDefined() && !ctx.arg.growableTable) {
limits.Flags |= WASM_LIMITS_FLAG_HAS_MAX;
limits.Maximum = limits.Minimum;
}
if (ctx.arg.is64.value_or(false))
limits.Flags |= WASM_LIMITS_FLAG_IS_64;
WasmSym::indirectFunctionTable->setLimits(limits);
}
static void scanRelocations() {
for (ObjFile *file : ctx.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 : ctx.syntheticFunctions)
out.functionSec->addFunction(func);
for (ObjFile *file : ctx.objectFiles) {
LLVM_DEBUG(dbgs() << "Functions: " << file->getName() << "\n");
for (InputFunction *func : file->functions)
out.functionSec->addFunction(func);
}
for (InputGlobal *global : ctx.syntheticGlobals)
out.globalSec->addGlobal(global);
for (ObjFile *file : ctx.objectFiles) {
LLVM_DEBUG(dbgs() << "Globals: " << file->getName() << "\n");
for (InputGlobal *global : file->globals)
out.globalSec->addGlobal(global);
}
for (ObjFile *file : ctx.objectFiles) {
LLVM_DEBUG(dbgs() << "Tags: " << file->getName() << "\n");
for (InputTag *tag : file->tags)
out.tagSec->addTag(tag);
}
for (ObjFile *file : ctx.objectFiles) {
LLVM_DEBUG(dbgs() << "Tables: " << file->getName() << "\n");
for (InputTable *table : file->tables)
out.tableSec->addTable(table);
}
for (InputTable *table : ctx.syntheticTables)
out.tableSec->addTable(table);
out.globalSec->assignIndexes();
out.tableSec->assignIndexes();
}
static StringRef getOutputDataSegmentName(const InputChunk &seg) {
// We always merge .tbss and .tdata into a single TLS segment so all TLS
// symbols are be relative to single __tls_base.
if (seg.isTLS())
return ".tdata";
if (!ctx.arg.mergeDataSegments)
return seg.name;
if (seg.name.starts_with(".text."))
return ".text";
if (seg.name.starts_with(".data."))
return ".data";
if (seg.name.starts_with(".bss."))
return ".bss";
if (seg.name.starts_with(".rodata."))
return ".rodata";
return seg.name;
}
OutputSegment *Writer::createOutputSegment(StringRef name) {
LLVM_DEBUG(dbgs() << "new segment: " << name << "\n");
OutputSegment *s = make<OutputSegment>(name);
if (ctx.arg.sharedMemory)
s->initFlags = WASM_DATA_SEGMENT_IS_PASSIVE;
if (!ctx.arg.relocatable && name.starts_with(".bss"))
s->isBss = true;
segments.push_back(s);
return s;
}
void Writer::createOutputSegments() {
for (ObjFile *file : ctx.objectFiles) {
for (InputChunk *segment : file->segments) {
if (!segment->live)
continue;
StringRef name = getOutputDataSegmentName(*segment);
OutputSegment *s = nullptr;
// When running in relocatable mode we can't merge segments that are part
// of comdat groups since the ultimate linker needs to be able exclude or
// include them individually.
if (ctx.arg.relocatable && !segment->getComdatName().empty()) {
s = createOutputSegment(name);
} else {
if (segmentMap.count(name) == 0)
segmentMap[name] = createOutputSegment(name);
s = segmentMap[name];
}
s->addInputSegment(segment);
}
}
// Sort segments by type, placing .bss last
std::stable_sort(segments.begin(), segments.end(),
[](const OutputSegment *a, const OutputSegment *b) {
auto order = [](StringRef name) {
return StringSwitch<int>(name)
.StartsWith(".tdata", 0)
.StartsWith(".rodata", 1)
.StartsWith(".data", 2)
.StartsWith(".bss", 4)
.Default(3);
};
return order(a->name) < order(b->name);
});
for (size_t i = 0; i < segments.size(); ++i)
segments[i]->index = i;
// Merge MergeInputSections into a single MergeSyntheticSection.
LLVM_DEBUG(dbgs() << "-- finalize input semgments\n");
for (OutputSegment *seg : segments)
seg->finalizeInputSegments();
}
void Writer::combineOutputSegments() {
// With PIC code we currently only support a single active data segment since
// we only have a single __memory_base to use as our base address. This pass
// combines all data segments into a single .data segment.
// This restriction does not apply when the extended const extension is
// available: https://github.com/WebAssembly/extended-const
assert(!ctx.arg.extendedConst);
assert(ctx.isPic && !ctx.arg.sharedMemory);
if (segments.size() <= 1)
return;
OutputSegment *combined = make<OutputSegment>(".data");
combined->startVA = segments[0]->startVA;
std::vector<OutputSegment *> newSegments = {combined};
for (OutputSegment *s : segments) {
if (!s->requiredInBinary()) {
newSegments.push_back(s);
continue;
}
bool first = true;
for (InputChunk *inSeg : s->inputSegments) {
if (first)
inSeg->alignment = std::max(inSeg->alignment, s->alignment);
first = false;
#ifndef NDEBUG
uint64_t oldVA = inSeg->getVA();
#endif
combined->addInputSegment(inSeg);
#ifndef NDEBUG
uint64_t newVA = inSeg->getVA();
LLVM_DEBUG(dbgs() << "added input segment. name=" << inSeg->name
<< " oldVA=" << oldVA << " newVA=" << newVA << "\n");
assert(oldVA == newVA);
#endif
}
}
segments = newSegments;
}
static void createFunction(DefinedFunction *func, StringRef bodyContent) {
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>(func->function)->setBody(body);
}
bool Writer::needsPassiveInitialization(const OutputSegment *segment) {
// If bulk memory features is supported then we can perform bss initialization
// (via memory.fill) during `__wasm_init_memory`.
if (ctx.arg.memoryImport.has_value() && !segment->requiredInBinary())
return true;
return segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE;
}
bool Writer::hasPassiveInitializedSegments() {
return llvm::any_of(segments, [this](const OutputSegment *s) {
return this->needsPassiveInitialization(s);
});
}
void Writer::createSyntheticInitFunctions() {
if (ctx.arg.relocatable)
return;
static WasmSignature nullSignature = {{}, {}};
createApplyDataRelocationsFunction();
// Passive segments are used to avoid memory being reinitialized on each
// thread's instantiation. These passive segments are initialized and
// dropped in __wasm_init_memory, which is registered as the start function
// We also initialize bss segments (using memory.fill) as part of this
// function.
if (hasPassiveInitializedSegments()) {
WasmSym::initMemory = symtab->addSyntheticFunction(
"__wasm_init_memory", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(nullSignature, "__wasm_init_memory"));
WasmSym::initMemory->markLive();
if (ctx.arg.sharedMemory) {
// This global is assigned during __wasm_init_memory in the shared memory
// case.
WasmSym::tlsBase->markLive();
}
}
if (ctx.arg.sharedMemory) {
if (out.globalSec->needsTLSRelocations()) {
WasmSym::applyGlobalTLSRelocs = symtab->addSyntheticFunction(
"__wasm_apply_global_tls_relocs", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(nullSignature,
"__wasm_apply_global_tls_relocs"));
WasmSym::applyGlobalTLSRelocs->markLive();
// TLS relocations depend on the __tls_base symbols
WasmSym::tlsBase->markLive();
}
auto hasTLSRelocs = [](const OutputSegment *segment) {
if (segment->isTLS())
for (const auto* is: segment->inputSegments)
if (is->getRelocations().size())
return true;
return false;
};
if (llvm::any_of(segments, hasTLSRelocs)) {
WasmSym::applyTLSRelocs = symtab->addSyntheticFunction(
"__wasm_apply_tls_relocs", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(nullSignature,
"__wasm_apply_tls_relocs"));
WasmSym::applyTLSRelocs->markLive();
}
}
if (ctx.isPic && out.globalSec->needsRelocations()) {
WasmSym::applyGlobalRelocs = symtab->addSyntheticFunction(
"__wasm_apply_global_relocs", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(nullSignature, "__wasm_apply_global_relocs"));
WasmSym::applyGlobalRelocs->markLive();
}
// If there is only one start function we can just use that function
// itself as the Wasm start function, otherwise we need to synthesize
// a new function to call them in sequence.
if (WasmSym::applyGlobalRelocs && WasmSym::initMemory) {
WasmSym::startFunction = symtab->addSyntheticFunction(
"__wasm_start", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(nullSignature, "__wasm_start"));
WasmSym::startFunction->markLive();
}
}
void Writer::createInitMemoryFunction() {
LLVM_DEBUG(dbgs() << "createInitMemoryFunction\n");
assert(WasmSym::initMemory);
assert(hasPassiveInitializedSegments());
uint64_t flagAddress;
if (ctx.arg.sharedMemory) {
assert(WasmSym::initMemoryFlag);
flagAddress = WasmSym::initMemoryFlag->getVA();
}
bool is64 = ctx.arg.is64.value_or(false);
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
// Initialize memory in a thread-safe manner. The thread that successfully
// increments the flag from 0 to 1 is responsible for performing the memory
// initialization. Other threads go sleep on the flag until the first thread
// finishing initializing memory, increments the flag to 2, and wakes all
// the other threads. Once the flag has been set to 2, subsequently started
// threads will skip the sleep. All threads unconditionally drop their
// passive data segments once memory has been initialized. The generated
// code is as follows:
//
// (func $__wasm_init_memory
// (block $drop
// (block $wait
// (block $init
// (br_table $init $wait $drop
// (i32.atomic.rmw.cmpxchg align=2 offset=0
// (i32.const $__init_memory_flag)
// (i32.const 0)
// (i32.const 1)
// )
// )
// ) ;; $init
// ( ... initialize data segments ... )
// (i32.atomic.store align=2 offset=0
// (i32.const $__init_memory_flag)
// (i32.const 2)
// )
// (drop
// (i32.atomic.notify align=2 offset=0
// (i32.const $__init_memory_flag)
// (i32.const -1u)
// )
// )
// (br $drop)
// ) ;; $wait
// (drop
// (i32.atomic.wait align=2 offset=0
// (i32.const $__init_memory_flag)
// (i32.const 1)
// (i32.const -1)
// )
// )
// ) ;; $drop
// ( ... drop data segments ... )
// )
//
// When we are building with PIC, calculate the flag location using:
//
// (global.get $__memory_base)
// (i32.const $__init_memory_flag)
// (i32.const 1)
auto writeGetFlagAddress = [&]() {
if (ctx.isPic) {
writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
writeUleb128(os, 0, "local 0");
} else {
writePtrConst(os, flagAddress, is64, "flag address");
}
};
if (ctx.arg.sharedMemory) {
// With PIC code we cache the flag address in local 0
if (ctx.isPic) {
writeUleb128(os, 1, "num local decls");
writeUleb128(os, 2, "local count");
writeU8(os, is64 ? WASM_TYPE_I64 : WASM_TYPE_I32, "address type");
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(), "memory_base");
writePtrConst(os, flagAddress, is64, "flag address");
writeU8(os, is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD, "add");
writeU8(os, WASM_OPCODE_LOCAL_SET, "local.set");
writeUleb128(os, 0, "local 0");
} else {
writeUleb128(os, 0, "num locals");
}
// Set up destination blocks
writeU8(os, WASM_OPCODE_BLOCK, "block $drop");
writeU8(os, WASM_TYPE_NORESULT, "block type");
writeU8(os, WASM_OPCODE_BLOCK, "block $wait");
writeU8(os, WASM_TYPE_NORESULT, "block type");
writeU8(os, WASM_OPCODE_BLOCK, "block $init");
writeU8(os, WASM_TYPE_NORESULT, "block type");
// Atomically check whether we win the race.
writeGetFlagAddress();
writeI32Const(os, 0, "expected flag value");
writeI32Const(os, 1, "new flag value");
writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
writeUleb128(os, WASM_OPCODE_I32_RMW_CMPXCHG, "i32.atomic.rmw.cmpxchg");
writeMemArg(os, 2, 0);
// Based on the value, decide what to do next.
writeU8(os, WASM_OPCODE_BR_TABLE, "br_table");
writeUleb128(os, 2, "label vector length");
writeUleb128(os, 0, "label $init");
writeUleb128(os, 1, "label $wait");
writeUleb128(os, 2, "default label $drop");
// Initialize passive data segments
writeU8(os, WASM_OPCODE_END, "end $init");
} else {
writeUleb128(os, 0, "num local decls");
}
for (const OutputSegment *s : segments) {
if (needsPassiveInitialization(s)) {
// For passive BSS segments we can simple issue a memory.fill(0).
// For non-BSS segments we do a memory.init. Both these
// instructions take as their first argument the destination
// address.
writePtrConst(os, s->startVA, is64, "destination address");
if (ctx.isPic) {
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(),
"__memory_base");
writeU8(os, is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD,
"i32.add");
}
// When we initialize the TLS segment we also set the `__tls_base`
// global. This allows the runtime to use this static copy of the
// TLS data for the first/main thread.
if (ctx.arg.sharedMemory && s->isTLS()) {
if (ctx.isPic) {
// Cache the result of the addionion in local 0
writeU8(os, WASM_OPCODE_LOCAL_TEE, "local.tee");
writeUleb128(os, 1, "local 1");
} else {
writePtrConst(os, s->startVA, is64, "destination address");
}
writeU8(os, WASM_OPCODE_GLOBAL_SET, "GLOBAL_SET");
writeUleb128(os, WasmSym::tlsBase->getGlobalIndex(),
"__tls_base");
if (ctx.isPic) {
writeU8(os, WASM_OPCODE_LOCAL_GET, "local.tee");
writeUleb128(os, 1, "local 1");
}
}
if (s->isBss) {
writeI32Const(os, 0, "fill value");
writePtrConst(os, s->size, is64, "memory region size");
writeU8(os, WASM_OPCODE_MISC_PREFIX, "bulk-memory prefix");
writeUleb128(os, WASM_OPCODE_MEMORY_FILL, "memory.fill");
writeU8(os, 0, "memory index immediate");
} else {
writeI32Const(os, 0, "source segment offset");
writeI32Const(os, s->size, "memory region size");
writeU8(os, WASM_OPCODE_MISC_PREFIX, "bulk-memory prefix");
writeUleb128(os, WASM_OPCODE_MEMORY_INIT, "memory.init");
writeUleb128(os, s->index, "segment index immediate");
writeU8(os, 0, "memory index immediate");
}
}
}
if (ctx.arg.sharedMemory) {
// Set flag to 2 to mark end of initialization
writeGetFlagAddress();
writeI32Const(os, 2, "flag value");
writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
writeUleb128(os, WASM_OPCODE_I32_ATOMIC_STORE, "i32.atomic.store");
writeMemArg(os, 2, 0);
// Notify any waiters that memory initialization is complete
writeGetFlagAddress();
writeI32Const(os, -1, "number of waiters");
writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
writeUleb128(os, WASM_OPCODE_ATOMIC_NOTIFY, "atomic.notify");
writeMemArg(os, 2, 0);
writeU8(os, WASM_OPCODE_DROP, "drop");
// Branch to drop the segments
writeU8(os, WASM_OPCODE_BR, "br");
writeUleb128(os, 1, "label $drop");
// Wait for the winning thread to initialize memory
writeU8(os, WASM_OPCODE_END, "end $wait");
writeGetFlagAddress();
writeI32Const(os, 1, "expected flag value");
writeI64Const(os, -1, "timeout");
writeU8(os, WASM_OPCODE_ATOMICS_PREFIX, "atomics prefix");
writeUleb128(os, WASM_OPCODE_I32_ATOMIC_WAIT, "i32.atomic.wait");
writeMemArg(os, 2, 0);
writeU8(os, WASM_OPCODE_DROP, "drop");
// Unconditionally drop passive data segments
writeU8(os, WASM_OPCODE_END, "end $drop");
}
for (const OutputSegment *s : segments) {
if (needsPassiveInitialization(s) && !s->isBss) {
// The TLS region should not be dropped since its is needed
// during the initialization of each thread (__wasm_init_tls).
if (ctx.arg.sharedMemory && s->isTLS())
continue;
// data.drop instruction
writeU8(os, WASM_OPCODE_MISC_PREFIX, "bulk-memory prefix");
writeUleb128(os, WASM_OPCODE_DATA_DROP, "data.drop");
writeUleb128(os, s->index, "segment index immediate");
}
}
// End the function
writeU8(os, WASM_OPCODE_END, "END");
}
createFunction(WasmSym::initMemory, bodyContent);
}
void Writer::createStartFunction() {
// If the start function exists when we have more than one function to call.
if (WasmSym::initMemory && WasmSym::applyGlobalRelocs) {
assert(WasmSym::startFunction);
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
writeUleb128(os, 0, "num locals");
writeU8(os, WASM_OPCODE_CALL, "CALL");
writeUleb128(os, WasmSym::applyGlobalRelocs->getFunctionIndex(),
"function index");
writeU8(os, WASM_OPCODE_CALL, "CALL");
writeUleb128(os, WasmSym::initMemory->getFunctionIndex(),
"function index");
writeU8(os, WASM_OPCODE_END, "END");
}
createFunction(WasmSym::startFunction, bodyContent);
} else if (WasmSym::initMemory) {
WasmSym::startFunction = WasmSym::initMemory;
} else if (WasmSym::applyGlobalRelocs) {
WasmSym::startFunction = WasmSym::applyGlobalRelocs;
}
}
// 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_data_relocs` and is expected to be called before
// any user code (i.e. before `__wasm_call_ctors`).
void Writer::createApplyDataRelocationsFunction() {
LLVM_DEBUG(dbgs() << "createApplyDataRelocationsFunction\n");
// First write the body's contents to a string.
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
writeUleb128(os, 0, "num locals");
bool generated = false;
for (const OutputSegment *seg : segments)
if (!ctx.arg.sharedMemory || !seg->isTLS())
for (const InputChunk *inSeg : seg->inputSegments)
generated |= inSeg->generateRelocationCode(os);
if (!generated) {
LLVM_DEBUG(dbgs() << "skipping empty __wasm_apply_data_relocs\n");
return;
}
writeU8(os, WASM_OPCODE_END, "END");
}
// __wasm_apply_data_relocs
// Function that applies relocations to data segment post-instantiation.
static WasmSignature nullSignature = {{}, {}};
auto def = symtab->addSyntheticFunction(
"__wasm_apply_data_relocs",
WASM_SYMBOL_VISIBILITY_DEFAULT | WASM_SYMBOL_EXPORTED,
make<SyntheticFunction>(nullSignature, "__wasm_apply_data_relocs"));
def->markLive();
createFunction(def, bodyContent);
}
void Writer::createApplyTLSRelocationsFunction() {
LLVM_DEBUG(dbgs() << "createApplyTLSRelocationsFunction\n");
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
writeUleb128(os, 0, "num locals");
for (const OutputSegment *seg : segments)
if (seg->isTLS())
for (const InputChunk *inSeg : seg->inputSegments)
inSeg->generateRelocationCode(os);
writeU8(os, WASM_OPCODE_END, "END");
}
createFunction(WasmSym::applyTLSRelocs, bodyContent);
}
// Similar to createApplyDataRelocationsFunction but generates relocation code
// for WebAssembly globals. Because these globals are not shared between threads
// these relocation need to run on every thread.
void Writer::createApplyGlobalRelocationsFunction() {
// First write the body's contents to a string.
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
writeUleb128(os, 0, "num locals");
out.globalSec->generateRelocationCode(os, false);
writeU8(os, WASM_OPCODE_END, "END");
}
createFunction(WasmSym::applyGlobalRelocs, bodyContent);
}
// Similar to createApplyGlobalRelocationsFunction but for
// TLS symbols. This cannot be run during the start function
// but must be delayed until __wasm_init_tls is called.
void Writer::createApplyGlobalTLSRelocationsFunction() {
// First write the body's contents to a string.
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
writeUleb128(os, 0, "num locals");
out.globalSec->generateRelocationCode(os, true);
writeU8(os, WASM_OPCODE_END, "END");
}
createFunction(WasmSym::applyGlobalTLSRelocs, bodyContent);
}
// Create synthetic "__wasm_call_ctors" function based on ctor functions
// in input object.
void Writer::createCallCtorsFunction() {
// If __wasm_call_ctors isn't referenced, there aren't any ctors, don't
// define the `__wasm_call_ctors` function.
if (!WasmSym::callCtors->isLive() && initFunctions.empty())
return;
// First write the body's contents to a string.
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
writeUleb128(os, 0, "num locals");
// Call constructors
for (const WasmInitEntry &f : initFunctions) {
writeU8(os, WASM_OPCODE_CALL, "CALL");
writeUleb128(os, f.sym->getFunctionIndex(), "function index");
for (size_t i = 0; i < f.sym->signature->Returns.size(); i++) {
writeU8(os, WASM_OPCODE_DROP, "DROP");
}
}
writeU8(os, WASM_OPCODE_END, "END");
}
createFunction(WasmSym::callCtors, bodyContent);
}
// Create a wrapper around a function export which calls the
// static constructors and destructors.
void Writer::createCommandExportWrapper(uint32_t functionIndex,
DefinedFunction *f) {
// First write the body's contents to a string.
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
writeUleb128(os, 0, "num locals");
// Call `__wasm_call_ctors` which call static constructors (and
// applies any runtime relocations in Emscripten-style PIC mode)
if (WasmSym::callCtors->isLive()) {
writeU8(os, WASM_OPCODE_CALL, "CALL");
writeUleb128(os, WasmSym::callCtors->getFunctionIndex(),
"function index");
}
// Call the user's code, leaving any return values on the operand stack.
for (size_t i = 0; i < f->signature->Params.size(); ++i) {
writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
writeUleb128(os, i, "local index");
}
writeU8(os, WASM_OPCODE_CALL, "CALL");
writeUleb128(os, functionIndex, "function index");
// Call the function that calls the destructors.
if (DefinedFunction *callDtors = WasmSym::callDtors) {
writeU8(os, WASM_OPCODE_CALL, "CALL");
writeUleb128(os, callDtors->getFunctionIndex(), "function index");
}
// End the function, returning the return values from the user's code.
writeU8(os, WASM_OPCODE_END, "END");
}
createFunction(f, bodyContent);
}
void Writer::createInitTLSFunction() {
std::string bodyContent;
{
raw_string_ostream os(bodyContent);
OutputSegment *tlsSeg = nullptr;
for (auto *seg : segments) {
if (seg->name == ".tdata") {
tlsSeg = seg;
break;
}
}
writeUleb128(os, 0, "num locals");
if (tlsSeg) {
writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
writeUleb128(os, 0, "local index");
writeU8(os, WASM_OPCODE_GLOBAL_SET, "global.set");
writeUleb128(os, WasmSym::tlsBase->getGlobalIndex(), "global index");
// FIXME(wvo): this local needs to be I64 in wasm64, or we need an extend op.
writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
writeUleb128(os, 0, "local index");
writeI32Const(os, 0, "segment offset");
writeI32Const(os, tlsSeg->size, "memory region size");
writeU8(os, WASM_OPCODE_MISC_PREFIX, "bulk-memory prefix");
writeUleb128(os, WASM_OPCODE_MEMORY_INIT, "MEMORY.INIT");
writeUleb128(os, tlsSeg->index, "segment index immediate");
writeU8(os, 0, "memory index immediate");
}
if (WasmSym::applyTLSRelocs) {
writeU8(os, WASM_OPCODE_CALL, "CALL");
writeUleb128(os, WasmSym::applyTLSRelocs->getFunctionIndex(),
"function index");
}
if (WasmSym::applyGlobalTLSRelocs) {
writeU8(os, WASM_OPCODE_CALL, "CALL");
writeUleb128(os, WasmSym::applyGlobalTLSRelocs->getFunctionIndex(),
"function index");
}
writeU8(os, WASM_OPCODE_END, "end function");
}
createFunction(WasmSym::initTLS, bodyContent);
}
// 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 (!ctx.arg.relocatable && !WasmSym::callCtors->isLive())
return;
for (ObjFile *file : ctx.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() || !sym->isLive())
continue;
if (sym->signature->Params.size() != 0)
error("constructor functions cannot take arguments: " + toString(*sym));
LLVM_DEBUG(dbgs() << "initFunctions: " << toString(*sym) << "\n");
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.tagSec = make<TagSection>();
out.globalSec = make<GlobalSection>();
out.exportSec = make<ExportSection>();
out.startSec = make<StartSection>();
out.elemSec = make<ElemSection>();
out.producersSec = make<ProducersSection>();
out.targetFeaturesSec = make<TargetFeaturesSection>();
out.buildIdSec = make<BuildIdSection>();
}
void Writer::createSyntheticSectionsPostLayout() {
out.dataCountSec = make<DataCountSection>(segments);
out.linkingSec = make<LinkingSection>(initFunctions, segments);
out.nameSec = make<NameSection>(segments);
}
void Writer::run() {
// 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 (!ctx.isPic && WasmSym::definedTableBase)
WasmSym::definedTableBase->setVA(ctx.arg.tableBase);
log("-- createOutputSegments");
createOutputSegments();
log("-- createSyntheticSections");
createSyntheticSections();
log("-- layoutMemory");
layoutMemory();
if (!ctx.arg.relocatable) {
// Create linker synthesized __start_SECNAME/__stop_SECNAME symbols
// This has to be done after memory layout is performed.
for (const OutputSegment *seg : segments) {
addStartStopSymbols(seg);
}
}
for (auto &pair : ctx.arg.exportedSymbols) {
Symbol *sym = symtab->find(pair.first());
if (sym && sym->isDefined())
sym->forceExport = true;
}
// Delay reporting errors about explicit exports until after
// addStartStopSymbols which can create optional symbols.
for (auto &name : ctx.arg.requiredExports) {
Symbol *sym = symtab->find(name);
if (!sym || !sym->isDefined()) {
if (ctx.arg.unresolvedSymbols == UnresolvedPolicy::ReportError)
error(Twine("symbol exported via --export not found: ") + name);
if (ctx.arg.unresolvedSymbols == UnresolvedPolicy::Warn)
warn(Twine("symbol exported via --export not found: ") + name);
}
}
log("-- populateTargetFeatures");
populateTargetFeatures();
// When outputting PIC code each segment lives at at fixes offset from the
// `__memory_base` import. Unless we support the extended const expression we
// can't do addition inside the constant expression, so we much combine the
// segments into a single one that can live at `__memory_base`.
if (ctx.isPic && !ctx.arg.extendedConst && !ctx.arg.sharedMemory) {
// In shared memory mode all data segments are passive and initialized
// via __wasm_init_memory.
log("-- combineOutputSegments");
combineOutputSegments();
}
log("-- createSyntheticSectionsPostLayout");
createSyntheticSectionsPostLayout();
log("-- populateProducers");
populateProducers();
log("-- calculateImports");
calculateImports();
log("-- scanRelocations");
scanRelocations();
log("-- finalizeIndirectFunctionTable");
finalizeIndirectFunctionTable();
log("-- createSyntheticInitFunctions");
createSyntheticInitFunctions();
log("-- assignIndexes");
assignIndexes();
log("-- calculateInitFunctions");
calculateInitFunctions();
if (!ctx.arg.relocatable) {
// Create linker synthesized functions
if (WasmSym::applyGlobalRelocs)
createApplyGlobalRelocationsFunction();
if (WasmSym::applyTLSRelocs)
createApplyTLSRelocationsFunction();
if (WasmSym::applyGlobalTLSRelocs)
createApplyGlobalTLSRelocationsFunction();
if (WasmSym::initMemory)
createInitMemoryFunction();
createStartFunction();
createCallCtorsFunction();
// Create export wrappers for commands if needed.
//
// If the input contains a call to `__wasm_call_ctors`, either in one of
// the input objects or an explicit export from the command-line, we
// assume ctors and dtors are taken care of already.
if (!ctx.arg.relocatable && !ctx.isPic &&
!WasmSym::callCtors->isUsedInRegularObj &&
!WasmSym::callCtors->isExported()) {
log("-- createCommandExportWrappers");
createCommandExportWrappers();
}
}
if (WasmSym::initTLS && WasmSym::initTLS->isLive()) {
log("-- createInitTLSFunction");
createInitTLSFunction();
}
if (errorCount())
return;
log("-- calculateTypes");
calculateTypes();
log("-- calculateExports");
calculateExports();
log("-- calculateCustomSections");
calculateCustomSections();
log("-- populateSymtab");
populateSymtab();
log("-- checkImportExportTargetFeatures");
checkImportExportTargetFeatures();
log("-- addSections");
addSections();
if (errorHandler().verbose) {
log("Defined Functions: " + Twine(out.functionSec->inputFunctions.size()));
log("Defined Globals : " + Twine(out.globalSec->numGlobals()));
log("Defined Tags : " + Twine(out.tagSec->inputTags.size()));
log("Defined Tables : " + Twine(out.tableSec->inputTables.size()));
log("Function Imports : " +
Twine(out.importSec->getNumImportedFunctions()));
log("Global Imports : " + Twine(out.importSec->getNumImportedGlobals()));
log("Tag Imports : " + Twine(out.importSec->getNumImportedTags()));
log("Table Imports : " + Twine(out.importSec->getNumImportedTables()));
}
createHeader();
log("-- finalizeSections");
finalizeSections();
log("-- writeMapFile");
writeMapFile(outputSections);
log("-- openFile");
openFile();
if (errorCount())
return;
writeHeader();
log("-- writeSections");
writeSections();
writeBuildId();
if (errorCount())
return;
if (Error e = buffer->commit())
fatal("failed to write output '" + buffer->getPath() +
"': " + toString(std::move(e)));
}
// Open a result file.
void Writer::openFile() {
log("writing: " + ctx.arg.outputFile);
Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
FileOutputBuffer::create(ctx.arg.outputFile, fileSize,
FileOutputBuffer::F_executable);
if (!bufferOrErr)
error("failed to open " + ctx.arg.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");
fileSize += header.size();
}
void writeResult() { Writer().run(); }
} // namespace wasm::lld
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