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//===--- CompatibilityOverride.cpp - Back-deploying compatibility fixes ---s-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// Support back-deploying compatibility fixes for newer apps running on older runtimes.
//
//===----------------------------------------------------------------------===//
#include "CompatibilityOverride.h"
#ifdef SWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT
#include "../runtime/ImageInspection.h"
#include "swift/Runtime/Once.h"
#include <assert.h>
#include <atomic>
#include <mach-o/getsect.h>
#include <type_traits>
using namespace swift;
/// The definition of the contents of the override section.
///
/// The runtime looks in the main executable (not any libraries!) for a
/// __swift54_hooks section and uses the hooks defined therein. This struct
/// defines the layout of that section. These hooks allow extending
/// runtime functionality when running apps built with a more recent
/// compiler. If additional hooks are needed, they may be added at the
/// end, but once ABI stability hits, existing ones must not be removed
/// or rearranged. The version number at the beginning can be used to
/// indicate the presence of added functions. Until we do so, the
/// version must be set to 0.
struct OverrideSection {
uintptr_t version;
#define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
Override_ ## name name;
#include COMPATIBILITY_OVERRIDE_INCLUDE_PATH
};
static_assert(std::is_pod<OverrideSection>::value,
"OverrideSection has a set layout and must be POD.");
// We only support mach-o for overrides, so the implementation of lookupSection
// can be mach-o specific.
#if __POINTER_WIDTH__ == 64
using mach_header_platform = mach_header_64;
#else
using mach_header_platform = mach_header;
#endif
extern "C" mach_header_platform *_NSGetMachExecuteHeader();
static void *lookupSection(const char *segment, const char *section,
size_t *outSize) {
unsigned long size;
auto *executableHeader = _NSGetMachExecuteHeader();
uint8_t *data = getsectiondata(executableHeader, segment, section, &size);
if (outSize != nullptr && data != nullptr)
*outSize = size;
return static_cast<void *>(data);
}
static OverrideSection *getOverrideSectionPtr() {
static OverrideSection *OverrideSectionPtr;
static swift_once_t Predicate;
swift_once(&Predicate, [](void *) {
size_t Size;
OverrideSectionPtr = static_cast<OverrideSection *>(
lookupSection("__DATA", COMPATIBILITY_OVERRIDE_SECTION_NAME, &Size));
if (Size < sizeof(OverrideSection))
OverrideSectionPtr = nullptr;
}, nullptr);
return OverrideSectionPtr;
}
#define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
Override_ ## name swift::getOverride_ ## name() { \
auto *Section = getOverrideSectionPtr(); \
if (Section == nullptr) \
return nullptr; \
return Section->name; \
}
#define OVERRIDE_NORETURN(name, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
Override_ ## name swift::getOverride_ ## name() { \
auto *Section = getOverrideSectionPtr(); \
if (Section == nullptr) \
nullptr; \
Section->name; \
}
#include COMPATIBILITY_OVERRIDE_INCLUDE_PATH
#endif // #ifdef SWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT
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