e555277780
The main changes are in: include/lld/Core/Reference.h include/lld/ReaderWriter/Reader.h Everything else is details to support the main change. 1) Registration based Readers Previously, lld had a tangled interdependency with all the Readers. It would have been impossible to make a streamlined linker (say for a JIT) which just supported one file format and one architecture (no yaml, no archives, etc). The old model also required a LinkingContext to read an object file, which would have made .o inspection tools awkward. The new model is that there is a global Registry object. You programmatically register the Readers you want with the registry object. Whenever you need to read/parse a file, you ask the registry to do it, and the registry tries each registered reader. For ease of use with the existing lld code base, there is one Registry object inside the LinkingContext object. 2) Changing kind value to be a tuple Beside Readers, the registry also keeps track of the mapping for Reference Kind values to and from strings. Along with that, this patch also fixes an ambiguity with the previous Reference::Kind values. The problem was that we wanted to reuse existing relocation type values as Reference::Kind values. But then how can the YAML write know how to convert a value to a string? The fix is to change the 32-bit Reference::Kind into a tuple with an 8-bit namespace (e.g. ELF, COFFF, etc), an 8-bit architecture (e.g. x86_64, PowerPC, etc), and a 16-bit value. This tuple system allows conversion to and from strings with no ambiguities. llvm-svn: 197727
67 lines
2.4 KiB
C++
67 lines
2.4 KiB
C++
//===- Passes/StubsPass.cpp - Adds stubs ----------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This linker pass updates call-sites which have references to shared library
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// atoms to instead have a reference to a stub (PLT entry) for the specified
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// symbol. Each file format defines a subclass of StubsPass which implements
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// the abstract methods for creating the file format specific StubAtoms.
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//
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//===----------------------------------------------------------------------===//
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#include "lld/Core/DefinedAtom.h"
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#include "lld/Core/File.h"
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#include "lld/Core/LLVM.h"
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#include "lld/Core/Pass.h"
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#include "lld/Core/Reference.h"
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#include "llvm/ADT/DenseMap.h"
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namespace lld {
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void StubsPass::perform(std::unique_ptr<MutableFile> &mergedFile) {
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// Skip this pass if output format uses text relocations instead of stubs.
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if (!this->noTextRelocs())
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return;
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// Scan all references in all atoms.
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for (const DefinedAtom *atom : mergedFile->defined()) {
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for (const Reference *ref : *atom) {
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// Look at call-sites.
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if (!this->isCallSite(*ref))
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continue;
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const Atom *target = ref->target();
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assert(target != nullptr);
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if (target->definition() == Atom::definitionSharedLibrary) {
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// Calls to shared libraries go through stubs.
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replaceCalleeWithStub(target, ref);
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continue;
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}
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const DefinedAtom *defTarget = dyn_cast<DefinedAtom>(target);
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if (defTarget && defTarget->interposable() != DefinedAtom::interposeNo) {
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// Calls to interposable functions in same linkage unit must also go
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// through a stub.
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assert(defTarget->scope() != DefinedAtom::scopeTranslationUnit);
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replaceCalleeWithStub(target, ref);
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}
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}
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}
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// Add all created stubs and support Atoms.
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this->addStubAtoms(*mergedFile);
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}
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void StubsPass::replaceCalleeWithStub(const Atom *target,
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const Reference *ref) {
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// Make file-format specific stub and other support atoms.
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const DefinedAtom *stub = this->getStub(*target);
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assert(stub != nullptr);
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// Switch call site to reference stub atom instead.
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const_cast<Reference *>(ref)->setTarget(stub);
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}
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} // end namespace lld
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