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//===- Passes/StubsPass.cpp - Adds stubs ----------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This linker pass updates call-sites which have references to shared library
// atoms to instead have a reference to a stub (PLT entry) for the specified
// symbol. Each file format defines a subclass of StubsPass which implements
// the abstract methods for creating the file format specific StubAtoms.
//
//===----------------------------------------------------------------------===//
#include "lld/Core/DefinedAtom.h"
#include "lld/Core/File.h"
#include "lld/Core/LLVM.h"
#include "lld/Core/Pass.h"
#include "lld/Core/Reference.h"
#include "llvm/ADT/DenseMap.h"
namespace lld {
void StubsPass::perform(std::unique_ptr<MutableFile> &mergedFile) {
// Skip this pass if output format uses text relocations instead of stubs.
if ( ! this->noTextRelocs() )
return;
// Scan all references in all atoms.
for (const DefinedAtom *atom : mergedFile->defined()) {
for (const Reference *ref : *atom) {
// Look at call-sites.
if (this->isCallSite(ref->kind()) ) {
const Atom* target = ref->target();
assert(target != nullptr);
bool replaceCalleeWithStub = false;
if ( target->definition() == Atom::definitionSharedLibrary ) {
// Calls to shared libraries go through stubs.
replaceCalleeWithStub = true;
}
else if (const DefinedAtom* defTarget =
dyn_cast<DefinedAtom>(target)) {
if ( defTarget->interposable() != DefinedAtom::interposeNo ) {
// Calls to interposable functions in same linkage unit
// must also go through a stub.
assert(defTarget->scope() != DefinedAtom::scopeTranslationUnit);
replaceCalleeWithStub = true;
}
}
if ( replaceCalleeWithStub ) {
// Make file-format specific stub and other support atoms.
const DefinedAtom* stub = this->getStub(*target);
assert(stub != nullptr);
// Switch call site to reference stub atom instead.
(const_cast<Reference*>(ref))->setTarget(stub);
}
}
}
}
// Add all created stubs and support Atoms.
this->addStubAtoms(*mergedFile);
}
}
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