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//===- Symbols.cpp --------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "Error.h"
#include "InputFiles.h"
#include "Symbols.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm::object;
using llvm::sys::fs::identify_magic;
using llvm::sys::fs::file_magic;
namespace lld {
namespace coff {
// As an approximation, regular symbols win over bitcode symbols, but we
// definitely have a conflict if the regular symbol is not replaceable and
// neither is the bitcode symbol. We do not replicate the rest of the symbol
// resolution logic here; symbol resolution will be done accurately after
// lowering bitcode symbols to regular symbols in addCombinedLTOObject().
static int compareRegularBitcode(DefinedRegular *R, DefinedBitcode *B) {
if (!R->isCommon() && !R->isCOMDAT() && !B->isReplaceable())
return 0;
return 1;
}
// Returns 1, 0 or -1 if this symbol should take precedence over the
// Other in the symbol table, tie or lose, respectively.
int Defined::compare(SymbolBody *Other) {
if (!isa<Defined>(Other))
return 1;
auto *X = dyn_cast<DefinedRegular>(this);
if (!X)
return 0;
if (auto *B = dyn_cast<DefinedBitcode>(Other))
return compareRegularBitcode(X, B);
auto *Y = dyn_cast<DefinedRegular>(Other);
if (!Y)
return 0;
// Common symbols are weaker than other types of defined symbols.
if (X->isCommon() && Y->isCommon())
return (X->getCommonSize() < Y->getCommonSize()) ? -1 : 1;
// TODO: we are not sure if regular defined symbol and common
// symbols are allowed to have the same name.
if (X->isCommon())
return -1;
if (Y->isCommon())
return 1;
if (X->isCOMDAT() && Y->isCOMDAT())
return 1;
return 0;
}
int DefinedBitcode::compare(SymbolBody *Other) {
if (!isa<Defined>(Other))
return 1;
if (auto *R = dyn_cast<DefinedRegular>(Other))
return -compareRegularBitcode(R, this);
if (auto *B = dyn_cast<DefinedBitcode>(Other)) {
if (!isReplaceable() && !B->isReplaceable())
return 0;
// Non-replaceable symbols win.
return isReplaceable() ? -1 : 1;
}
return 0;
}
int Lazy::compare(SymbolBody *Other) {
if (isa<Defined>(Other))
return -1;
// Undefined symbols with weak aliases will turn into defined
// symbols if they remain undefined, so we don't need to resolve
// such symbols.
if (auto *U = dyn_cast<Undefined>(Other))
if (U->getWeakAlias())
return -1;
return 1;
}
int Undefined::compare(SymbolBody *Other) {
if (isa<Defined>(Other))
return -1;
if (isa<Lazy>(Other))
return getWeakAlias() ? 1 : -1;
if (cast<Undefined>(Other)->getWeakAlias())
return -1;
return 1;
}
StringRef DefinedRegular::getName() {
// DefinedSymbol's name is read lazily for a performance reason.
// Non-external symbol names are never used by the linker
// except for logging or debugging.
// Their internal references are resolved not by name but by symbol index.
// And because they are not external, no one can refer them by name.
// Object files contain lots of non-external symbols, and creating
// StringRefs for them (which involves lots of strlen() on the string table)
// is a waste of time.
if (Name.empty())
COFFFile->getSymbolName(Sym, Name);
return Name;
}
ErrorOr<std::unique_ptr<InputFile>> Lazy::getMember() {
auto MBRefOrErr = File->getMember(&Sym);
if (auto EC = MBRefOrErr.getError())
return EC;
MemoryBufferRef MBRef = MBRefOrErr.get();
// getMember returns an empty buffer if the member was already
// read from the library.
if (MBRef.getBuffer().empty())
return std::unique_ptr<InputFile>(nullptr);
file_magic Magic = identify_magic(MBRef.getBuffer());
if (Magic == file_magic::bitcode)
return std::unique_ptr<InputFile>(new BitcodeFile(MBRef));
if (Magic == file_magic::coff_import_library)
return std::unique_ptr<InputFile>(new ImportFile(MBRef));
if (Magic != file_magic::coff_object) {
llvm::errs() << File->getName() << ": unknown file type\n";
return make_error_code(LLDError::InvalidFile);
}
std::unique_ptr<InputFile> Obj(new ObjectFile(MBRef));
Obj->setParentName(File->getName());
return std::move(Obj);
}
} // namespace coff
} // namespace lld
|
