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110 lines
3.9 KiB
C++
110 lines
3.9 KiB
C++
//===--- ProtocolConformance.cpp - Swift protocol conformance checking ----===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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//
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// Checking and caching of Swift protocol conformances.
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//
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// This implementation is intended to be backward-deployed into Swift 5.0
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// runtimes.
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//
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//===----------------------------------------------------------------------===//
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#include "../../public/runtime/Private.h"
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#include "Overrides.h"
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#include "swift/Threading/Once.h"
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#include <dlfcn.h>
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#include <mach-o/dyld.h>
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#include <mach-o/getsect.h>
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#include <objc/runtime.h>
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using namespace swift;
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#if __POINTER_WIDTH__ == 64
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using mach_header_platform = mach_header_64;
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#else
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using mach_header_platform = mach_header;
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#endif
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/// The Mach-O section name for the section containing protocol conformances.
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/// This lives within SEG_TEXT.
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constexpr const char ProtocolConformancesSection[] = "__swift5_proto";
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// A dummy target context descriptor to use in conformance records which point
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// to a NULL descriptor. It doesn't have to be completely valid, just something
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// that code reading conformance descriptors will ignore.
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struct {
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ContextDescriptorFlags flags;
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int32_t offset;
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} DummyTargetContextDescriptor = {
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ContextDescriptorFlags().withKind(ContextDescriptorKind::Extension),
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0
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};
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// Search for any protocol conformance descriptors with a NULL type descriptor
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// and rewrite those to point to the dummy descriptor. This occurs when an
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// extension is used to declare a conformance on a weakly linked type and that
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// type is not present at runtime.
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static void addImageCallback(const mach_header *mh, intptr_t vmaddr_slide) {
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unsigned long size;
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const uint8_t *section =
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getsectiondata(reinterpret_cast<const mach_header_platform *>(mh),
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SEG_TEXT, ProtocolConformancesSection,
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&size);
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if (!section)
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return;
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auto recordsBegin
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= reinterpret_cast<const ProtocolConformanceRecord*>(section);
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auto recordsEnd
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= reinterpret_cast<const ProtocolConformanceRecord*>
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(section + size);
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for (auto record = recordsBegin; record != recordsEnd; ++record) {
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auto descriptor = record->get();
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if (auto typePtr = descriptor->_getTypeDescriptorLocation()) {
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if (*typePtr == nullptr)
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*typePtr = reinterpret_cast<TargetContextDescriptor<InProcess> *>(
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&DummyTargetContextDescriptor);
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}
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}
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}
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// Register the add image callback with dyld.
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static void registerAddImageCallback(void *) {
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_dyld_register_func_for_add_image(addImageCallback);
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}
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// Defined in libswiftCompatibility51, which is always linked if we link against
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// libswiftCompatibility50
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const Metadata *_swiftoverride_class_getSuperclass(const Metadata *theClass);
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const WitnessTable *
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swift::swift50override_conformsToProtocol(const Metadata *type,
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const ProtocolDescriptor *protocol,
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ConformsToProtocol_t *original_conformsToProtocol)
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{
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// Register our add image callback if necessary.
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static swift::once_t token;
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swift::once(token, registerAddImageCallback, nullptr);
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// The implementation of swift_conformsToProtocol in Swift 5.0 would return
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// a false negative answer when asking whether a subclass conforms using
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// a conformance from a superclass. Work around this by walking up the
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// superclass chain in cases where the original implementation returns
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// null.
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do {
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auto result = original_conformsToProtocol(type, protocol);
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if (result)
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return result;
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} while ((type = _swiftoverride_class_getSuperclass(type)));
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return nullptr;
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}
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