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95 lines
3.5 KiB
C++
95 lines
3.5 KiB
C++
//===--- CompatibiltyOverride.cpp - Back-deploying compatibility fies ---s-===//
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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 - 2018 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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// Support back-deploying compatibility fixes for newer apps running on older runtimes.
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//
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//===----------------------------------------------------------------------===//
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#include "CompatibilityOverride.h"
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#ifdef SWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT
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#include "../runtime/ImageInspection.h"
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#include "swift/Runtime/Once.h"
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#include <assert.h>
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#include <atomic>
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#include <mach-o/getsect.h>
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#include <type_traits>
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using namespace swift;
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/// The definition of the contents of the override section.
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///
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/// The runtime looks in the main executable (not any libraries!) for a
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/// __swift54_hooks section and uses the hooks defined therein. This struct
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/// defines the layout of that section. These hooks allow extending
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/// runtime functionality when running apps built with a more recent
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/// compiler. If additional hooks are needed, they may be added at the
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/// end, but once ABI stability hits, existing ones must not be removed
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/// or rearranged. The version number at the beginning can be used to
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/// indicate the presence of added functions. Until we do so, the
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/// version must be set to 0.
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struct OverrideSection {
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uintptr_t version;
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#define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
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Override_ ## name name;
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#include COMPATIBILITY_OVERRIDE_INCLUDE_PATH
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};
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static_assert(std::is_pod<OverrideSection>::value,
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"OverrideSection has a set layout and must be POD.");
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// We only support mach-o for overrides, so the implementation of lookupSection
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// can be mach-o specific.
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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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extern "C" mach_header_platform *_NSGetMachExecuteHeader();
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static void *lookupSection(const char *segment, const char *section,
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size_t *outSize) {
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unsigned long size;
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auto *executableHeader = _NSGetMachExecuteHeader();
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uint8_t *data = getsectiondata(executableHeader, segment, section, &size);
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if (outSize != nullptr && data != nullptr)
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*outSize = size;
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return static_cast<void *>(data);
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}
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static OverrideSection *getOverrideSectionPtr() {
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static OverrideSection *OverrideSectionPtr;
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static swift_once_t Predicate;
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swift_once(&Predicate, [](void *) {
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size_t Size;
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OverrideSectionPtr = static_cast<OverrideSection *>(
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lookupSection("__DATA", COMPATIBILITY_OVERRIDE_SECTION_NAME, &Size));
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if (Size < sizeof(OverrideSection))
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OverrideSectionPtr = nullptr;
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}, nullptr);
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return OverrideSectionPtr;
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}
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#define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
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Override_ ## name swift::getOverride_ ## name() { \
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auto *Section = getOverrideSectionPtr(); \
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if (Section == nullptr) \
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return nullptr; \
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return Section->name; \
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}
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#include COMPATIBILITY_OVERRIDE_INCLUDE_PATH
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#endif // #ifdef SWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT
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