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| //===- Core/SymbolTable.cpp - Main Symbol Table ---------------------------===//
//
// 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 "lld/Core/SymbolTable.h"
#include "lld/Common/LLVM.h"
#include "lld/Core/AbsoluteAtom.h"
#include "lld/Core/Atom.h"
#include "lld/Core/DefinedAtom.h"
#include "lld/Core/File.h"
#include "lld/Core/LinkingContext.h"
#include "lld/Core/Resolver.h"
#include "lld/Core/SharedLibraryAtom.h"
#include "lld/Core/UndefinedAtom.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdlib>
#include <vector>
namespace lld {
bool SymbolTable::add(const UndefinedAtom &atom) { return addByName(atom); }
bool SymbolTable::add(const SharedLibraryAtom &atom) { return addByName(atom); }
bool SymbolTable::add(const AbsoluteAtom &atom) { return addByName(atom); }
bool SymbolTable::add(const DefinedAtom &atom) {
if (!atom.name().empty() &&
atom.scope() != DefinedAtom::scopeTranslationUnit) {
// Named atoms cannot be merged by content.
assert(atom.merge() != DefinedAtom::mergeByContent);
// Track named atoms that are not scoped to file (static).
return addByName(atom);
}
if (atom.merge() == DefinedAtom::mergeByContent) {
// Named atoms cannot be merged by content.
assert(atom.name().empty());
// Currently only read-only constants can be merged.
if (atom.permissions() == DefinedAtom::permR__)
return addByContent(atom);
// TODO: support mergeByContent of data atoms by comparing content & fixups.
}
return false;
}
enum NameCollisionResolution {
NCR_First,
NCR_Second,
NCR_DupDef,
NCR_DupUndef,
NCR_DupShLib,
NCR_Error
};
static NameCollisionResolution cases[4][4] = {
//regular absolute undef sharedLib
{
// first is regular
NCR_DupDef, NCR_Error, NCR_First, NCR_First
},
{
// first is absolute
NCR_Error, NCR_Error, NCR_First, NCR_First
},
{
// first is undef
NCR_Second, NCR_Second, NCR_DupUndef, NCR_Second
},
{
// first is sharedLib
NCR_Second, NCR_Second, NCR_First, NCR_DupShLib
}
};
static NameCollisionResolution collide(Atom::Definition first,
Atom::Definition second) {
return cases[first][second];
}
enum MergeResolution {
MCR_First,
MCR_Second,
MCR_Largest,
MCR_SameSize,
MCR_Error
};
static MergeResolution mergeCases[][6] = {
// no tentative weak weakAddress sameNameAndSize largest
{MCR_Error, MCR_First, MCR_First, MCR_First, MCR_SameSize, MCR_Largest}, // no
{MCR_Second, MCR_Largest, MCR_Second, MCR_Second, MCR_SameSize, MCR_Largest}, // tentative
{MCR_Second, MCR_First, MCR_First, MCR_Second, MCR_SameSize, MCR_Largest}, // weak
{MCR_Second, MCR_First, MCR_First, MCR_First, MCR_SameSize, MCR_Largest}, // weakAddress
{MCR_SameSize, MCR_SameSize, MCR_SameSize, MCR_SameSize, MCR_SameSize, MCR_SameSize}, // sameSize
{MCR_Largest, MCR_Largest, MCR_Largest, MCR_Largest, MCR_SameSize, MCR_Largest}, // largest
};
static MergeResolution mergeSelect(DefinedAtom::Merge first,
DefinedAtom::Merge second) {
assert(first != DefinedAtom::mergeByContent);
assert(second != DefinedAtom::mergeByContent);
return mergeCases[first][second];
}
bool SymbolTable::addByName(const Atom &newAtom) {
StringRef name = newAtom.name();
assert(!name.empty());
const Atom *existing = findByName(name);
if (existing == nullptr) {
// Name is not in symbol table yet, add it associate with this atom.
_nameTable[name] = &newAtom;
return true;
}
// Do nothing if the same object is added more than once.
if (existing == &newAtom)
return false;
// Name is already in symbol table and associated with another atom.
bool useNew = true;
switch (collide(existing->definition(), newAtom.definition())) {
case NCR_First:
useNew = false;
break;
case NCR_Second:
useNew = true;
break;
case NCR_DupDef: {
const auto *existingDef = cast<DefinedAtom>(existing);
const auto *newDef = cast<DefinedAtom>(&newAtom);
switch (mergeSelect(existingDef->merge(), newDef->merge())) {
case MCR_First:
useNew = false;
break;
case MCR_Second:
useNew = true;
break;
case MCR_Largest: {
uint64_t existingSize = existingDef->sectionSize();
uint64_t newSize = newDef->sectionSize();
useNew = (newSize >= existingSize);
break;
}
case MCR_SameSize: {
uint64_t existingSize = existingDef->sectionSize();
uint64_t newSize = newDef->sectionSize();
if (existingSize == newSize) {
useNew = true;
break;
}
llvm::errs() << "Size mismatch: "
<< existing->name() << " (" << existingSize << ") "
<< newAtom.name() << " (" << newSize << ")\n";
LLVM_FALLTHROUGH;
}
case MCR_Error:
llvm::errs() << "Duplicate symbols: "
<< existing->name()
<< ":"
<< existing->file().path()
<< " and "
<< newAtom.name()
<< ":"
<< newAtom.file().path()
<< "\n";
llvm::report_fatal_error("duplicate symbol error");
break;
}
break;
}
case NCR_DupUndef: {
const UndefinedAtom* existingUndef = cast<UndefinedAtom>(existing);
const UndefinedAtom* newUndef = cast<UndefinedAtom>(&newAtom);
bool sameCanBeNull = (existingUndef->canBeNull() == newUndef->canBeNull());
if (sameCanBeNull)
useNew = false;
else
useNew = (newUndef->canBeNull() < existingUndef->canBeNull());
break;
}
case NCR_DupShLib: {
useNew = false;
break;
}
case NCR_Error:
llvm::errs() << "SymbolTable: error while merging " << name << "\n";
llvm::report_fatal_error("duplicate symbol error");
break;
}
if (useNew) {
// Update name table to use new atom.
_nameTable[name] = &newAtom;
// Add existing atom to replacement table.
_replacedAtoms[existing] = &newAtom;
} else {
// New atom is not being used. Add it to replacement table.
_replacedAtoms[&newAtom] = existing;
}
return false;
}
unsigned SymbolTable::AtomMappingInfo::getHashValue(const DefinedAtom *atom) {
auto content = atom->rawContent();
return llvm::hash_combine(atom->size(),
atom->contentType(),
llvm::hash_combine_range(content.begin(),
content.end()));
}
bool SymbolTable::AtomMappingInfo::isEqual(const DefinedAtom * const l,
const DefinedAtom * const r) {
if (l == r)
return true;
if (l == getEmptyKey() || r == getEmptyKey())
return false;
if (l == getTombstoneKey() || r == getTombstoneKey())
return false;
if (l->contentType() != r->contentType())
return false;
if (l->size() != r->size())
return false;
if (l->sectionChoice() != r->sectionChoice())
return false;
if (l->sectionChoice() == DefinedAtom::sectionCustomRequired) {
if (!l->customSectionName().equals(r->customSectionName()))
return false;
}
ArrayRef<uint8_t> lc = l->rawContent();
ArrayRef<uint8_t> rc = r->rawContent();
return memcmp(lc.data(), rc.data(), lc.size()) == 0;
}
bool SymbolTable::addByContent(const DefinedAtom &newAtom) {
AtomContentSet::iterator pos = _contentTable.find(&newAtom);
if (pos == _contentTable.end()) {
_contentTable.insert(&newAtom);
return true;
}
const Atom* existing = *pos;
// New atom is not being used. Add it to replacement table.
_replacedAtoms[&newAtom] = existing;
return false;
}
const Atom *SymbolTable::findByName(StringRef sym) {
NameToAtom::iterator pos = _nameTable.find(sym);
if (pos == _nameTable.end())
return nullptr;
return pos->second;
}
const Atom *SymbolTable::replacement(const Atom *atom) {
// Find the replacement for a given atom. Atoms in _replacedAtoms
// may be chained, so find the last one.
for (;;) {
AtomToAtom::iterator pos = _replacedAtoms.find(atom);
if (pos == _replacedAtoms.end())
return atom;
atom = pos->second;
}
}
bool SymbolTable::isCoalescedAway(const Atom *atom) {
return _replacedAtoms.count(atom) > 0;
}
std::vector<const UndefinedAtom *> SymbolTable::undefines() {
std::vector<const UndefinedAtom *> ret;
for (auto it : _nameTable) {
const Atom *atom = it.second;
assert(atom != nullptr);
if (const auto *undef = dyn_cast<const UndefinedAtom>(atom))
if (_replacedAtoms.count(undef) == 0)
ret.push_back(undef);
}
return ret;
}
} // namespace lld
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