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InputFiles.cpp
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//===- InputFiles.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 "InputFiles.h"
#include "COFFLinkerContext.h"
#include "Chunks.h"
#include "Config.h"
#include "DebugTypes.h"
#include "Driver.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "lld/Common/DWARF.h"
#include "llvm-c/lto.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/COFF.h"
#include "llvm/DebugInfo/CodeView/DebugSubsectionRecord.h"
#include "llvm/DebugInfo/CodeView/SymbolDeserializer.h"
#include "llvm/DebugInfo/CodeView/SymbolRecord.h"
#include "llvm/DebugInfo/CodeView/TypeDeserializer.h"
#include "llvm/DebugInfo/PDB/Native/NativeSession.h"
#include "llvm/DebugInfo/PDB/Native/PDBFile.h"
#include "llvm/IR/Mangler.h"
#include "llvm/LTO/LTO.h"
#include "llvm/Object/Binary.h"
#include "llvm/Object/COFF.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Path.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/TargetParser/Triple.h"
#include <cstring>
#include <optional>
#include <system_error>
#include <utility>
using namespace llvm;
using namespace llvm::COFF;
using namespace llvm::codeview;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::coff;
using llvm::Triple;
using llvm::support::ulittle32_t;
// Returns the last element of a path, which is supposed to be a filename.
static StringRef getBasename(StringRef path) {
return sys::path::filename(path, sys::path::Style::windows);
}
// Returns a string in the format of "foo.obj" or "foo.obj(bar.lib)".
std::string lld::toString(const coff::InputFile *file) {
if (!file)
return "<internal>";
if (file->parentName.empty())
return std::string(file->getName());
return (getBasename(file->parentName) + "(" + getBasename(file->getName()) +
")")
.str();
}
const COFFSyncStream &coff::operator<<(const COFFSyncStream &s,
const InputFile *f) {
return s << toString(f);
}
/// Checks that Source is compatible with being a weak alias to Target.
/// If Source is Undefined and has no weak alias set, makes it a weak
/// alias to Target.
static void checkAndSetWeakAlias(SymbolTable &symtab, InputFile *f,
Symbol *source, Symbol *target,
bool isAntiDep) {
if (auto *u = dyn_cast<Undefined>(source)) {
if (u->weakAlias && u->weakAlias != target) {
// Ignore duplicated anti-dependency symbols.
if (isAntiDep)
return;
if (!u->isAntiDep) {
// Weak aliases as produced by GCC are named in the form
// .weak.<weaksymbol>.<othersymbol>, where <othersymbol> is the name
// of another symbol emitted near the weak symbol.
// Just use the definition from the first object file that defined
// this weak symbol.
if (symtab.ctx.config.allowDuplicateWeak)
return;
symtab.reportDuplicate(source, f);
}
}
u->setWeakAlias(target, isAntiDep);
}
}
static bool ignoredSymbolName(StringRef name) {
return name == "@feat.00" || name == "@comp.id";
}
ArchiveFile::ArchiveFile(COFFLinkerContext &ctx, MemoryBufferRef m)
: InputFile(ctx.symtab, ArchiveKind, m) {}
void ArchiveFile::parse() {
COFFLinkerContext &ctx = symtab.ctx;
// Parse a MemoryBufferRef as an archive file.
file = CHECK(Archive::create(mb), this);
// Try to read symbols from ECSYMBOLS section on ARM64EC.
if (ctx.symtabEC) {
iterator_range<Archive::symbol_iterator> symbols =
CHECK(file->ec_symbols(), this);
if (!symbols.empty()) {
for (const Archive::Symbol &sym : symbols)
ctx.symtabEC->addLazyArchive(this, sym);
// Read both EC and native symbols on ARM64X.
if (!ctx.hybridSymtab)
return;
}
}
// Read the symbol table to construct Lazy objects.
for (const Archive::Symbol &sym : file->symbols())
ctx.symtab.addLazyArchive(this, sym);
}
// Returns a buffer pointing to a member file containing a given symbol.
void ArchiveFile::addMember(const Archive::Symbol &sym) {
const Archive::Child &c =
CHECK(sym.getMember(), "could not get the member for symbol " +
toCOFFString(symtab.ctx, sym));
// Return an empty buffer if we have already returned the same buffer.
if (!seen.insert(c.getChildOffset()).second)
return;
symtab.ctx.driver.enqueueArchiveMember(c, sym, getName());
}
std::vector<MemoryBufferRef>
lld::coff::getArchiveMembers(COFFLinkerContext &ctx, Archive *file) {
std::vector<MemoryBufferRef> v;
Error err = Error::success();
// Thin archives refer to .o files, so --reproduces needs the .o files too.
bool addToTar = file->isThin() && ctx.driver.tar;
for (const Archive::Child &c : file->children(err)) {
MemoryBufferRef mbref =
CHECK(c.getMemoryBufferRef(),
file->getFileName() +
": could not get the buffer for a child of the archive");
if (addToTar) {
ctx.driver.tar->append(relativeToRoot(check(c.getFullName())),
mbref.getBuffer());
}
v.push_back(mbref);
}
if (err)
Fatal(ctx) << file->getFileName()
<< ": Archive::children failed: " << toString(std::move(err));
return v;
}
ObjFile::ObjFile(SymbolTable &symtab, COFFObjectFile *coffObj, bool lazy)
: InputFile(symtab, ObjectKind, coffObj->getMemoryBufferRef(), lazy),
coffObj(coffObj) {}
ObjFile *ObjFile::create(COFFLinkerContext &ctx, MemoryBufferRef m, bool lazy) {
// Parse a memory buffer as a COFF file.
Expected<std::unique_ptr<Binary>> bin = createBinary(m);
if (!bin)
Fatal(ctx) << "Could not parse " << m.getBufferIdentifier();
auto *obj = dyn_cast<COFFObjectFile>(bin->get());
if (!obj)
Fatal(ctx) << m.getBufferIdentifier() << " is not a COFF file";
bin->release();
return make<ObjFile>(ctx.getSymtab(MachineTypes(obj->getMachine())), obj,
lazy);
}
void ObjFile::parseLazy() {
// Native object file.
uint32_t numSymbols = coffObj->getNumberOfSymbols();
for (uint32_t i = 0; i < numSymbols; ++i) {
COFFSymbolRef coffSym = check(coffObj->getSymbol(i));
if (coffSym.isUndefined() || !coffSym.isExternal() ||
coffSym.isWeakExternal())
continue;
StringRef name = check(coffObj->getSymbolName(coffSym));
if (coffSym.isAbsolute() && ignoredSymbolName(name))
continue;
symtab.addLazyObject(this, name);
if (!lazy)
return;
i += coffSym.getNumberOfAuxSymbols();
}
}
struct ECMapEntry {
ulittle32_t src;
ulittle32_t dst;
ulittle32_t type;
};
void ObjFile::initializeECThunks() {
for (SectionChunk *chunk : hybmpChunks) {
if (chunk->getContents().size() % sizeof(ECMapEntry)) {
Err(symtab.ctx) << "Invalid .hybmp chunk size "
<< chunk->getContents().size();
continue;
}
const uint8_t *end =
chunk->getContents().data() + chunk->getContents().size();
for (const uint8_t *iter = chunk->getContents().data(); iter != end;
iter += sizeof(ECMapEntry)) {
auto entry = reinterpret_cast<const ECMapEntry *>(iter);
switch (entry->type) {
case Arm64ECThunkType::Entry:
symtab.addEntryThunk(getSymbol(entry->src), getSymbol(entry->dst));
break;
case Arm64ECThunkType::Exit:
symtab.addExitThunk(getSymbol(entry->src), getSymbol(entry->dst));
break;
case Arm64ECThunkType::GuestExit:
break;
default:
Warn(symtab.ctx) << "Ignoring unknown EC thunk type " << entry->type;
}
}
}
}
void ObjFile::parse() {
// Read section and symbol tables.
initializeChunks();
initializeSymbols();
initializeFlags();
initializeDependencies();
initializeECThunks();
}
const coff_section *ObjFile::getSection(uint32_t i) {
auto sec = coffObj->getSection(i);
if (!sec)
Fatal(symtab.ctx) << "getSection failed: #" << i << ": " << sec.takeError();
return *sec;
}
// We set SectionChunk pointers in the SparseChunks vector to this value
// temporarily to mark comdat sections as having an unknown resolution. As we
// walk the object file's symbol table, once we visit either a leader symbol or
// an associative section definition together with the parent comdat's leader,
// we set the pointer to either nullptr (to mark the section as discarded) or a
// valid SectionChunk for that section.
static SectionChunk *const pendingComdat = reinterpret_cast<SectionChunk *>(1);
void ObjFile::initializeChunks() {
uint32_t numSections = coffObj->getNumberOfSections();
sparseChunks.resize(numSections + 1);
for (uint32_t i = 1; i < numSections + 1; ++i) {
const coff_section *sec = getSection(i);
if (sec->Characteristics & IMAGE_SCN_LNK_COMDAT)
sparseChunks[i] = pendingComdat;
else
sparseChunks[i] = readSection(i, nullptr, "");
}
}
SectionChunk *ObjFile::readSection(uint32_t sectionNumber,
const coff_aux_section_definition *def,
StringRef leaderName) {
const coff_section *sec = getSection(sectionNumber);
StringRef name;
if (Expected<StringRef> e = coffObj->getSectionName(sec))
name = *e;
else
Fatal(symtab.ctx) << "getSectionName failed: #" << sectionNumber << ": "
<< e.takeError();
if (name == ".drectve") {
ArrayRef<uint8_t> data;
cantFail(coffObj->getSectionContents(sec, data));
directives = StringRef((const char *)data.data(), data.size());
return nullptr;
}
if (name == ".llvm_addrsig") {
addrsigSec = sec;
return nullptr;
}
if (name == ".llvm.call-graph-profile") {
callgraphSec = sec;
return nullptr;
}
// Object files may have DWARF debug info or MS CodeView debug info
// (or both).
//
// DWARF sections don't need any special handling from the perspective
// of the linker; they are just a data section containing relocations.
// We can just link them to complete debug info.
//
// CodeView needs linker support. We need to interpret debug info,
// and then write it to a separate .pdb file.
// Ignore DWARF debug info unless requested to be included.
if (!symtab.ctx.config.includeDwarfChunks && name.starts_with(".debug_"))
return nullptr;
if (sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_REMOVE)
return nullptr;
SectionChunk *c;
if (isArm64EC(getMachineType()))
c = make<SectionChunkEC>(this, sec);
else
c = make<SectionChunk>(this, sec);
if (def)
c->checksum = def->CheckSum;
// CodeView sections are stored to a different vector because they are not
// linked in the regular manner.
if (c->isCodeView())
debugChunks.push_back(c);
else if (name == ".gfids$y")
guardFidChunks.push_back(c);
else if (name == ".giats$y")
guardIATChunks.push_back(c);
else if (name == ".gljmp$y")
guardLJmpChunks.push_back(c);
else if (name == ".gehcont$y")
guardEHContChunks.push_back(c);
else if (name == ".sxdata")
sxDataChunks.push_back(c);
else if (isArm64EC(getMachineType()) && name == ".hybmp$x")
hybmpChunks.push_back(c);
else if (symtab.ctx.config.tailMerge && sec->NumberOfRelocations == 0 &&
name == ".rdata" && leaderName.starts_with("??_C@"))
// COFF sections that look like string literal sections (i.e. no
// relocations, in .rdata, leader symbol name matches the MSVC name mangling
// for string literals) are subject to string tail merging.
MergeChunk::addSection(symtab.ctx, c);
else if (name == ".rsrc" || name.starts_with(".rsrc$"))
resourceChunks.push_back(c);
else if (!(sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_INFO))
chunks.push_back(c);
return c;
}
void ObjFile::includeResourceChunks() {
chunks.insert(chunks.end(), resourceChunks.begin(), resourceChunks.end());
}
void ObjFile::readAssociativeDefinition(
COFFSymbolRef sym, const coff_aux_section_definition *def) {
readAssociativeDefinition(sym, def, def->getNumber(sym.isBigObj()));
}
void ObjFile::readAssociativeDefinition(COFFSymbolRef sym,
const coff_aux_section_definition *def,
uint32_t parentIndex) {
SectionChunk *parent = sparseChunks[parentIndex];
int32_t sectionNumber = sym.getSectionNumber();
auto diag = [&]() {
StringRef name = check(coffObj->getSymbolName(sym));
StringRef parentName;
const coff_section *parentSec = getSection(parentIndex);
if (Expected<StringRef> e = coffObj->getSectionName(parentSec))
parentName = *e;
Err(symtab.ctx) << toString(this) << ": associative comdat " << name
<< " (sec " << sectionNumber
<< ") has invalid reference to section " << parentName
<< " (sec " << parentIndex << ")";
};
if (parent == pendingComdat) {
// This can happen if an associative comdat refers to another associative
// comdat that appears after it (invalid per COFF spec) or to a section
// without any symbols.
diag();
return;
}
// Check whether the parent is prevailing. If it is, so are we, and we read
// the section; otherwise mark it as discarded.
if (parent) {
SectionChunk *c = readSection(sectionNumber, def, "");
sparseChunks[sectionNumber] = c;
if (c) {
c->selection = IMAGE_COMDAT_SELECT_ASSOCIATIVE;
parent->addAssociative(c);
}
} else {
sparseChunks[sectionNumber] = nullptr;
}
}
void ObjFile::recordPrevailingSymbolForMingw(
COFFSymbolRef sym, DenseMap<StringRef, uint32_t> &prevailingSectionMap) {
// For comdat symbols in executable sections, where this is the copy
// of the section chunk we actually include instead of discarding it,
// add the symbol to a map to allow using it for implicitly
// associating .[px]data$<func> sections to it.
// Use the suffix from the .text$<func> instead of the leader symbol
// name, for cases where the names differ (i386 mangling/decorations,
// cases where the leader is a weak symbol named .weak.func.default*).
int32_t sectionNumber = sym.getSectionNumber();
SectionChunk *sc = sparseChunks[sectionNumber];
if (sc && sc->getOutputCharacteristics() & IMAGE_SCN_MEM_EXECUTE) {
StringRef name = sc->getSectionName().split('$').second;
prevailingSectionMap[name] = sectionNumber;
}
}
void ObjFile::maybeAssociateSEHForMingw(
COFFSymbolRef sym, const coff_aux_section_definition *def,
const DenseMap<StringRef, uint32_t> &prevailingSectionMap) {
StringRef name = check(coffObj->getSymbolName(sym));
if (name.consume_front(".pdata$") || name.consume_front(".xdata$") ||
name.consume_front(".eh_frame$")) {
// For MinGW, treat .[px]data$<func> and .eh_frame$<func> as implicitly
// associative to the symbol <func>.
auto parentSym = prevailingSectionMap.find(name);
if (parentSym != prevailingSectionMap.end())
readAssociativeDefinition(sym, def, parentSym->second);
}
}
Symbol *ObjFile::createRegular(COFFSymbolRef sym) {
SectionChunk *sc = sparseChunks[sym.getSectionNumber()];
if (sym.isExternal()) {
StringRef name = check(coffObj->getSymbolName(sym));
if (sc)
return symtab.addRegular(this, name, sym.getGeneric(), sc,
sym.getValue());
// For MinGW symbols named .weak.* that point to a discarded section,
// don't create an Undefined symbol. If nothing ever refers to the symbol,
// everything should be fine. If something actually refers to the symbol
// (e.g. the undefined weak alias), linking will fail due to undefined
// references at the end.
if (symtab.ctx.config.mingw && name.starts_with(".weak."))
return nullptr;
return symtab.addUndefined(name, this, false);
}
if (sc)
return make<DefinedRegular>(this, /*Name*/ "", /*IsCOMDAT*/ false,
/*IsExternal*/ false, sym.getGeneric(), sc);
return nullptr;
}
void ObjFile::initializeSymbols() {
uint32_t numSymbols = coffObj->getNumberOfSymbols();
symbols.resize(numSymbols);
SmallVector<std::pair<Symbol *, const coff_aux_weak_external *>, 8>
weakAliases;
std::vector<uint32_t> pendingIndexes;
pendingIndexes.reserve(numSymbols);
DenseMap<StringRef, uint32_t> prevailingSectionMap;
std::vector<const coff_aux_section_definition *> comdatDefs(
coffObj->getNumberOfSections() + 1);
COFFLinkerContext &ctx = symtab.ctx;
for (uint32_t i = 0; i < numSymbols; ++i) {
COFFSymbolRef coffSym = check(coffObj->getSymbol(i));
bool prevailingComdat;
if (coffSym.isUndefined()) {
symbols[i] = createUndefined(coffSym, false);
} else if (coffSym.isWeakExternal()) {
auto aux = coffSym.getAux<coff_aux_weak_external>();
bool overrideLazy = true;
// On ARM64EC, external function calls emit a pair of weak-dependency
// aliases: func to #func and #func to the func guess exit thunk
// (instead of a single undefined func symbol, which would be emitted on
// other targets). Allow such aliases to be overridden by lazy archive
// symbols, just as we would for undefined symbols.
if (isArm64EC(getMachineType()) &&
aux->Characteristics == IMAGE_WEAK_EXTERN_ANTI_DEPENDENCY) {
COFFSymbolRef targetSym = check(coffObj->getSymbol(aux->TagIndex));
if (!targetSym.isAnyUndefined()) {
// If the target is defined, it may be either a guess exit thunk or
// the actual implementation. If it's the latter, consider the alias
// to be part of the implementation and override potential lazy
// archive symbols.
StringRef targetName = check(coffObj->getSymbolName(targetSym));
StringRef name = check(coffObj->getSymbolName(coffSym));
std::optional<std::string> mangledName =
getArm64ECMangledFunctionName(name);
overrideLazy = mangledName == targetName;
} else {
overrideLazy = false;
}
}
symbols[i] = createUndefined(coffSym, overrideLazy);
weakAliases.emplace_back(symbols[i], aux);
} else if (std::optional<Symbol *> optSym =
createDefined(coffSym, comdatDefs, prevailingComdat)) {
symbols[i] = *optSym;
if (ctx.config.mingw && prevailingComdat)
recordPrevailingSymbolForMingw(coffSym, prevailingSectionMap);
} else {
// createDefined() returns std::nullopt if a symbol belongs to a section
// that was pending at the point when the symbol was read. This can happen
// in two cases:
// 1) section definition symbol for a comdat leader;
// 2) symbol belongs to a comdat section associated with another section.
// In both of these cases, we can expect the section to be resolved by
// the time we finish visiting the remaining symbols in the symbol
// table. So we postpone the handling of this symbol until that time.
pendingIndexes.push_back(i);
}
i += coffSym.getNumberOfAuxSymbols();
}
for (uint32_t i : pendingIndexes) {
COFFSymbolRef sym = check(coffObj->getSymbol(i));
if (const coff_aux_section_definition *def = sym.getSectionDefinition()) {
if (def->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE)
readAssociativeDefinition(sym, def);
else if (ctx.config.mingw)
maybeAssociateSEHForMingw(sym, def, prevailingSectionMap);
}
if (sparseChunks[sym.getSectionNumber()] == pendingComdat) {
StringRef name = check(coffObj->getSymbolName(sym));
Log(ctx) << "comdat section " << name
<< " without leader and unassociated, discarding";
continue;
}
symbols[i] = createRegular(sym);
}
for (auto &kv : weakAliases) {
Symbol *sym = kv.first;
const coff_aux_weak_external *aux = kv.second;
checkAndSetWeakAlias(symtab, this, sym, symbols[aux->TagIndex],
aux->Characteristics ==
IMAGE_WEAK_EXTERN_ANTI_DEPENDENCY);
}
// Free the memory used by sparseChunks now that symbol loading is finished.
decltype(sparseChunks)().swap(sparseChunks);
}
Symbol *ObjFile::createUndefined(COFFSymbolRef sym, bool overrideLazy) {
StringRef name = check(coffObj->getSymbolName(sym));
Symbol *s = symtab.addUndefined(name, this, overrideLazy);
// Add an anti-dependency alias for undefined AMD64 symbols on the ARM64EC
// target.
if (symtab.isEC() && getMachineType() == AMD64) {
auto u = dyn_cast<Undefined>(s);
if (u && !u->weakAlias) {
if (std::optional<std::string> mangledName =
getArm64ECMangledFunctionName(name)) {
Symbol *m = symtab.addUndefined(saver().save(*mangledName), this,
/*overrideLazy=*/false);
u->setWeakAlias(m, /*antiDep=*/true);
}
}
}
return s;
}
static const coff_aux_section_definition *findSectionDef(COFFObjectFile *obj,
int32_t section) {
uint32_t numSymbols = obj->getNumberOfSymbols();
for (uint32_t i = 0; i < numSymbols; ++i) {
COFFSymbolRef sym = check(obj->getSymbol(i));
if (sym.getSectionNumber() != section)
continue;
if (const coff_aux_section_definition *def = sym.getSectionDefinition())
return def;
}
return nullptr;
}
void ObjFile::handleComdatSelection(
COFFSymbolRef sym, COMDATType &selection, bool &prevailing,
DefinedRegular *leader,
const llvm::object::coff_aux_section_definition *def) {
if (prevailing)
return;
// There's already an existing comdat for this symbol: `Leader`.
// Use the comdats's selection field to determine if the new
// symbol in `Sym` should be discarded, produce a duplicate symbol
// error, etc.
SectionChunk *leaderChunk = leader->getChunk();
COMDATType leaderSelection = leaderChunk->selection;
COFFLinkerContext &ctx = symtab.ctx;
assert(leader->data && "Comdat leader without SectionChunk?");
if (isa<BitcodeFile>(leader->file)) {
// If the leader is only a LTO symbol, we don't know e.g. its final size
// yet, so we can't do the full strict comdat selection checking yet.
selection = leaderSelection = IMAGE_COMDAT_SELECT_ANY;
}
if ((selection == IMAGE_COMDAT_SELECT_ANY &&
leaderSelection == IMAGE_COMDAT_SELECT_LARGEST) ||
(selection == IMAGE_COMDAT_SELECT_LARGEST &&
leaderSelection == IMAGE_COMDAT_SELECT_ANY)) {
// cl.exe picks "any" for vftables when building with /GR- and
// "largest" when building with /GR. To be able to link object files
// compiled with each flag, "any" and "largest" are merged as "largest".
leaderSelection = selection = IMAGE_COMDAT_SELECT_LARGEST;
}
// GCCs __declspec(selectany) doesn't actually pick "any" but "same size as".
// Clang on the other hand picks "any". To be able to link two object files
// with a __declspec(selectany) declaration, one compiled with gcc and the
// other with clang, we merge them as proper "same size as"
if (ctx.config.mingw && ((selection == IMAGE_COMDAT_SELECT_ANY &&
leaderSelection == IMAGE_COMDAT_SELECT_SAME_SIZE) ||
(selection == IMAGE_COMDAT_SELECT_SAME_SIZE &&
leaderSelection == IMAGE_COMDAT_SELECT_ANY))) {
leaderSelection = selection = IMAGE_COMDAT_SELECT_SAME_SIZE;
}
// Other than that, comdat selections must match. This is a bit more
// strict than link.exe which allows merging "any" and "largest" if "any"
// is the first symbol the linker sees, and it allows merging "largest"
// with everything (!) if "largest" is the first symbol the linker sees.
// Making this symmetric independent of which selection is seen first
// seems better though.
// (This behavior matches ModuleLinker::getComdatResult().)
if (selection != leaderSelection) {
Log(ctx) << "conflicting comdat type for " << leader << ": "
<< (int)leaderSelection << " in " << leader->getFile() << " and "
<< (int)selection << " in " << this;
symtab.reportDuplicate(leader, this);
return;
}
switch (selection) {
case IMAGE_COMDAT_SELECT_NODUPLICATES:
symtab.reportDuplicate(leader, this);
break;
case IMAGE_COMDAT_SELECT_ANY:
// Nothing to do.
break;
case IMAGE_COMDAT_SELECT_SAME_SIZE:
if (leaderChunk->getSize() != getSection(sym)->SizeOfRawData) {
if (!ctx.config.mingw) {
symtab.reportDuplicate(leader, this);
} else {
const coff_aux_section_definition *leaderDef = nullptr;
if (leaderChunk->file)
leaderDef = findSectionDef(leaderChunk->file->getCOFFObj(),
leaderChunk->getSectionNumber());
if (!leaderDef || leaderDef->Length != def->Length)
symtab.reportDuplicate(leader, this);
}
}
break;
case IMAGE_COMDAT_SELECT_EXACT_MATCH: {
SectionChunk newChunk(this, getSection(sym));
// link.exe only compares section contents here and doesn't complain
// if the two comdat sections have e.g. different alignment.
// Match that.
if (leaderChunk->getContents() != newChunk.getContents())
symtab.reportDuplicate(leader, this, &newChunk, sym.getValue());
break;
}
case IMAGE_COMDAT_SELECT_ASSOCIATIVE:
// createDefined() is never called for IMAGE_COMDAT_SELECT_ASSOCIATIVE.
// (This means lld-link doesn't produce duplicate symbol errors for
// associative comdats while link.exe does, but associate comdats
// are never extern in practice.)
llvm_unreachable("createDefined not called for associative comdats");
case IMAGE_COMDAT_SELECT_LARGEST:
if (leaderChunk->getSize() < getSection(sym)->SizeOfRawData) {
// Replace the existing comdat symbol with the new one.
StringRef name = check(coffObj->getSymbolName(sym));
// FIXME: This is incorrect: With /opt:noref, the previous sections
// make it into the final executable as well. Correct handling would
// be to undo reading of the whole old section that's being replaced,
// or doing one pass that determines what the final largest comdat
// is for all IMAGE_COMDAT_SELECT_LARGEST comdats and then reading
// only the largest one.
replaceSymbol<DefinedRegular>(leader, this, name, /*IsCOMDAT*/ true,
/*IsExternal*/ true, sym.getGeneric(),
nullptr);
prevailing = true;
}
break;
case IMAGE_COMDAT_SELECT_NEWEST:
llvm_unreachable("should have been rejected earlier");
}
}
std::optional<Symbol *> ObjFile::createDefined(
COFFSymbolRef sym,
std::vector<const coff_aux_section_definition *> &comdatDefs,
bool &prevailing) {
prevailing = false;
auto getName = [&]() { return check(coffObj->getSymbolName(sym)); };
if (sym.isCommon()) {
auto *c = make<CommonChunk>(sym);
chunks.push_back(c);
return symtab.addCommon(this, getName(), sym.getValue(), sym.getGeneric(),
c);
}
COFFLinkerContext &ctx = symtab.ctx;
if (sym.isAbsolute()) {
StringRef name = getName();
if (name == "@feat.00")
feat00Flags = sym.getValue();
// Skip special symbols.
if (ignoredSymbolName(name))
return nullptr;
if (sym.isExternal())
return symtab.addAbsolute(name, sym);
return make<DefinedAbsolute>(ctx, name, sym);
}
int32_t sectionNumber = sym.getSectionNumber();
if (sectionNumber == llvm::COFF::IMAGE_SYM_DEBUG)
return nullptr;
if (sym.isEmptySectionDeclaration()) {
// As there is no coff_section in the object file for these, make a
// new virtual one, with everything zeroed out (i.e. an empty section),
// with only the name and characteristics set.
StringRef name = getName();
auto *hdr = make<coff_section>();
memset(hdr, 0, sizeof(*hdr));
strncpy(hdr->Name, name.data(),
std::min(name.size(), (size_t)COFF::NameSize));
// We have no idea what characteristics should be assumed here; pick
// a default. This matches what is used for .idata sections in the regular
// object files in import libraries.
hdr->Characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ |
IMAGE_SCN_MEM_WRITE | IMAGE_SCN_ALIGN_4BYTES;
auto *sc = make<SectionChunk>(this, hdr);
chunks.push_back(sc);
return make<DefinedRegular>(this, /*name=*/"", /*isCOMDAT=*/false,
/*isExternal=*/false, sym.getGeneric(), sc);
}
if (llvm::COFF::isReservedSectionNumber(sectionNumber))
Fatal(ctx) << toString(this) << ": " << getName()
<< " should not refer to special section "
<< Twine(sectionNumber);
if ((uint32_t)sectionNumber >= sparseChunks.size())
Fatal(ctx) << toString(this) << ": " << getName()
<< " should not refer to non-existent section "
<< Twine(sectionNumber);
// Comdat handling.
// A comdat symbol consists of two symbol table entries.
// The first symbol entry has the name of the section (e.g. .text), fixed
// values for the other fields, and one auxiliary record.
// The second symbol entry has the name of the comdat symbol, called the
// "comdat leader".
// When this function is called for the first symbol entry of a comdat,
// it sets comdatDefs and returns std::nullopt, and when it's called for the
// second symbol entry it reads comdatDefs and then sets it back to nullptr.
// Handle comdat leader.
if (const coff_aux_section_definition *def = comdatDefs[sectionNumber]) {
comdatDefs[sectionNumber] = nullptr;
DefinedRegular *leader;
if (sym.isExternal()) {
std::tie(leader, prevailing) =
symtab.addComdat(this, getName(), sym.getGeneric());
} else {
leader = make<DefinedRegular>(this, /*Name*/ "", /*IsCOMDAT*/ false,
/*IsExternal*/ false, sym.getGeneric());
prevailing = true;
}
if (def->Selection < (int)IMAGE_COMDAT_SELECT_NODUPLICATES ||
// Intentionally ends at IMAGE_COMDAT_SELECT_LARGEST: link.exe
// doesn't understand IMAGE_COMDAT_SELECT_NEWEST either.
def->Selection > (int)IMAGE_COMDAT_SELECT_LARGEST) {
Fatal(ctx) << "unknown comdat type "
<< std::to_string((int)def->Selection) << " for " << getName()
<< " in " << toString(this);
}
COMDATType selection = (COMDATType)def->Selection;
if (leader->isCOMDAT)
handleComdatSelection(sym, selection, prevailing, leader, def);
if (prevailing) {
SectionChunk *c = readSection(sectionNumber, def, getName());
sparseChunks[sectionNumber] = c;
if (!c)
return nullptr;
c->sym = cast<DefinedRegular>(leader);
c->selection = selection;
cast<DefinedRegular>(leader)->data = &c->repl;
} else {
sparseChunks[sectionNumber] = nullptr;
}
return leader;
}
// Prepare to handle the comdat leader symbol by setting the section's
// ComdatDefs pointer if we encounter a non-associative comdat.
if (sparseChunks[sectionNumber] == pendingComdat) {
if (const coff_aux_section_definition *def = sym.getSectionDefinition()) {
if (def->Selection != IMAGE_COMDAT_SELECT_ASSOCIATIVE)
comdatDefs[sectionNumber] = def;
}
return std::nullopt;
}
return createRegular(sym);
}
MachineTypes ObjFile::getMachineType() const {
return static_cast<MachineTypes>(coffObj->getMachine());
}
ArrayRef<uint8_t> ObjFile::getDebugSection(StringRef secName) {
if (SectionChunk *sec = SectionChunk::findByName(debugChunks, secName))
return sec->consumeDebugMagic();
return {};
}
// OBJ files systematically store critical information in a .debug$S stream,
// even if the TU was compiled with no debug info. At least two records are
// always there. S_OBJNAME stores a 32-bit signature, which is loaded into the
// PCHSignature member. S_COMPILE3 stores compile-time cmd-line flags. This is
// currently used to initialize the hotPatchable member.
void ObjFile::initializeFlags() {
ArrayRef<uint8_t> data = getDebugSection(".debug$S");
if (data.empty())
return;
DebugSubsectionArray subsections;
BinaryStreamReader reader(data, llvm::endianness::little);
ExitOnError exitOnErr;
exitOnErr(reader.readArray(subsections, data.size()));
for (const DebugSubsectionRecord &ss : subsections) {
if (ss.kind() != DebugSubsectionKind::Symbols)
continue;
unsigned offset = 0;
// Only parse the first two records. We are only looking for S_OBJNAME
// and S_COMPILE3, and they usually appear at the beginning of the
// stream.
for (unsigned i = 0; i < 2; ++i) {
Expected<CVSymbol> sym = readSymbolFromStream(ss.getRecordData(), offset);
if (!sym) {
consumeError(sym.takeError());
return;
}
if (sym->kind() == SymbolKind::S_COMPILE3) {
auto cs =
cantFail(SymbolDeserializer::deserializeAs<Compile3Sym>(sym.get()));
hotPatchable =
(cs.Flags & CompileSym3Flags::HotPatch) != CompileSym3Flags::None;
}
if (sym->kind() == SymbolKind::S_OBJNAME) {
auto objName = cantFail(SymbolDeserializer::deserializeAs<ObjNameSym>(
sym.get()));
if (objName.Signature)
pchSignature = objName.Signature;
}
offset += sym->length();
}
}
}
// Depending on the compilation flags, OBJs can refer to external files,
// necessary to merge this OBJ into the final PDB. We currently support two
// types of external files: Precomp/PCH OBJs, when compiling with /Yc and /Yu.
// And PDB type servers, when compiling with /Zi. This function extracts these
// dependencies and makes them available as a TpiSource interface (see
// DebugTypes.h). Both cases only happen with cl.exe: clang-cl produces regular
// output even with /Yc and /Yu and with /Zi.
void ObjFile::initializeDependencies() {
COFFLinkerContext &ctx = symtab.ctx;
if (!ctx.config.debug)
return;
bool isPCH = false;
ArrayRef<uint8_t> data = getDebugSection(".debug$P");
if (!data.empty())
isPCH = true;
else
data = getDebugSection(".debug$T");
// symbols but no types, make a plain, empty TpiSource anyway, because it
// simplifies adding the symbols later.
if (data.empty()) {
if (!debugChunks.empty())
debugTypesObj = makeTpiSource(ctx, this);
return;
}
// Get the first type record. It will indicate if this object uses a type
// server (/Zi) or a PCH file (/Yu).
CVTypeArray types;
BinaryStreamReader reader(data, llvm::endianness::little);
cantFail(reader.readArray(types, reader.getLength()));
CVTypeArray::Iterator firstType = types.begin();
if (firstType == types.end())
return;
// Remember the .debug$T or .debug$P section.
debugTypes = data;
// This object file is a PCH file that others will depend on.
if (isPCH) {
debugTypesObj = makePrecompSource(ctx, this);
return;
}
// This object file was compiled with /Zi. Enqueue the PDB dependency.
if (firstType->kind() == LF_TYPESERVER2) {
TypeServer2Record ts = cantFail(
TypeDeserializer::deserializeAs<TypeServer2Record>(firstType->data()));
debugTypesObj = makeUseTypeServerSource(ctx, this, ts);
enqueuePdbFile(ts.getName(), this);
return;
}
// This object was compiled with /Yu. It uses types from another object file
// with a matching signature.
if (firstType->kind() == LF_PRECOMP) {
PrecompRecord precomp = cantFail(
TypeDeserializer::deserializeAs<PrecompRecord>(firstType->data()));
// We're better off trusting the LF_PRECOMP signature. In some cases the
// S_OBJNAME record doesn't contain a valid PCH signature.
if (precomp.Signature)
pchSignature = precomp.Signature;
debugTypesObj = makeUsePrecompSource(ctx, this, precomp);
// Drop the LF_PRECOMP record from the input stream.
debugTypes = debugTypes.drop_front(firstType->RecordData.size());
return;
}
// This is a plain old object file.
debugTypesObj = makeTpiSource(ctx, this);
}
// The casing of the PDB path stamped in the OBJ can differ from the actual path
// on disk. With this, we ensure to always use lowercase as a key for the
// pdbInputFileInstances map, at least on Windows.
static std::string normalizePdbPath(StringRef path) {
#if defined(_WIN32)
return path.lower();
#else // LINUX
return std::string(path);
#endif
}
// If existing, return the actual PDB path on disk.
static std::optional<std::string>
findPdbPath(StringRef pdbPath, ObjFile *dependentFile, StringRef outputPath) {
// Ensure the file exists before anything else. In some cases, if the path
// points to a removable device, Driver::enqueuePath() would fail with an
// error (EAGAIN, "resource unavailable try again") which we want to skip
// silently.
if (llvm::sys::fs::exists(pdbPath))
return normalizePdbPath(pdbPath);
StringRef objPath = !dependentFile->parentName.empty()
? dependentFile->parentName
: dependentFile->getName();
// Currently, type server PDBs are only created by MSVC cl, which only runs