stdlib/toolchain/CompatibilityDynamicReplacements/DynamicReplaceable.cpp

//===--- ProtocolConformance.cpp - Swift protocol conformance checking ----===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2019 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
//
//===----------------------------------------------------------------------===//
//
// Runtime support for dynamic replaceable functions.
//
// This implementation is intended to be backward-deployed into Swift 5.0
// runtimes.
//
//===----------------------------------------------------------------------===//

#include "swift/Runtime/Once.h"
#include "swift/Runtime/Exclusivity.h"
#include "../../public/runtime/ThreadLocalStorage.h"

using namespace swift;

__attribute__((visibility("hidden"), weak))
extern "C" char *swift_getFunctionReplacement50(char **ReplFnPtr, char *CurrFn) {
  // Call the current implementation if it is available.
  if (swift_getFunctionReplacement)
    return swift_getFunctionReplacement(ReplFnPtr, CurrFn);

  char *ReplFn = *ReplFnPtr;
  char *RawReplFn = ReplFn;

  if (RawReplFn == CurrFn)
    return nullptr;

  auto origKey =
      (uintptr_t)SWIFT_THREAD_GETSPECIFIC(SWIFT_COMPATIBILITY_50_TLS_KEY);
  if ((origKey & 0x1) != 0) {
    auto mask = ((uintptr_t)-1) < 1;
    auto resetKey = origKey & mask;
    SWIFT_THREAD_SETSPECIFIC(SWIFT_COMPATIBILITY_50_TLS_KEY, (void *)resetKey);
    return nullptr;
  }
  return ReplFn;
}

__attribute__((visibility("hidden"), weak))
extern "C" char *swift_getOrigOfReplaceable50(char **OrigFnPtr) {
  // Call the current implementation if it is available.
  if (swift_getOrigOfReplaceable)
    return swift_getOrigOfReplaceable(OrigFnPtr);

  char *OrigFn = *OrigFnPtr;
  auto origKey =
      (uintptr_t)SWIFT_THREAD_GETSPECIFIC(SWIFT_COMPATIBILITY_50_TLS_KEY);
  auto newKey = origKey | 0x1;
  SWIFT_THREAD_SETSPECIFIC(SWIFT_COMPATIBILITY_50_TLS_KEY, (void *)newKey);
  return OrigFn;
}

// Allow this library to get force-loaded by autolinking
__attribute__((weak, visibility("hidden")))
extern "C"
char _swift_FORCE_LOAD_$_swiftCompatibilityDynamicReplacements = 0;