stdlib/toolchain/Compatibility50/Overrides.cpp

//===--- Overrides.cpp - Compat override table for Swift 5.0 runtime ------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2020 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
//
//===----------------------------------------------------------------------===//
//
//  This file provides compatibility override hooks for Swift 5.0 runtimes.
//
//===----------------------------------------------------------------------===//

#include "Overrides.h"
#include "../Compatibility51/Overrides.h"
#include "CompatibilityOverride.h"

#include <dlfcn.h>
#include <mach-o/dyld.h>
#include <mach-o/getsect.h>

using namespace swift;

struct OverrideSection {
  uintptr_t version;
#define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
  Override_ ## name name;
#include "CompatibilityOverride.def"
};
  
OverrideSection Swift50Overrides
__attribute__((used, section("__DATA,__swift_hooks"))) = {
  .version = 0,
  .conformsToProtocol = swift50override_conformsToProtocol,
  // We use the same hook for conformsToSwiftProtocol as we do for a 5.1
  // runtime, so reference the override from the Compatibility51 library.
  // If we're back deploying to Swift 5.0, we also have to support 5.1, so
  // the Compatibility51 library is always linked when the 50 library is.
  .conformsToSwiftProtocol = swift51override_conformsToSwiftProtocol,
};

// Allow this library to get force-loaded by autolinking
__attribute__((weak, visibility("hidden")))
extern "C"
char _swift_FORCE_LOAD_$_swiftCompatibility50 = 0;

// Put a getClass hook in front of the system Swift runtime's hook to prevent it
// from trying to interpret symbolic references. rdar://problem/55036306

// FIXME: delete this #if and dlsym once we don't
// need to build with older libobjc headers
#if !OBJC_GETCLASSHOOK_DEFINED
using objc_hook_getClass =  BOOL(*)(const char * _Nonnull name,
                                    Class _Nullable * _Nonnull outClass);
#endif
static objc_hook_getClass OldGetClassHook;

static BOOL
getObjCClassByMangledName_untrusted(const char * _Nonnull typeName,
                                    Class _Nullable * _Nonnull outClass) {
  // Scan the string for byte sequences that might be recognized as
  // symbolic references, and reject them.
  for (const char *c = typeName; *c != 0; ++c) {
    if (*c >= 1 && *c < 0x20) {
      *outClass = Nil;
      return NO;
    }
  }
  
  if (OldGetClassHook) {
    return OldGetClassHook(typeName, outClass);
  }
  // In case the OS runtime for some reason didn't install a hook, fallback to
  // NO.
  return NO;
}

#if __POINTER_WIDTH__ == 64
using mach_header_platform = mach_header_64;
#else
using mach_header_platform = mach_header;
#endif

__attribute__((constructor))
static void installGetClassHook_untrusted() {
  // swiftCompatibility* might be linked into multiple dynamic libraries because
  // of build system reasons, but the copy in the main executable is the only
  // one that should count. Bail early unless we're running out of the main
  // executable.
  //
  // Newer versions of dyld add additional API that can determine this more
  // efficiently, but we have to support back to OS X 10.9/iOS 7, so dladdr
  // is the only API that reaches back that far.
  Dl_info dlinfo;
  if (dladdr((const void*)(uintptr_t)installGetClassHook_untrusted, &dlinfo) == 0)
    return;
  auto machHeader = (const mach_header_platform *)dlinfo.dli_fbase;
  if (machHeader->filetype != MH_EXECUTE)
    return;
  
  // FIXME: delete this #if and dlsym once we don't
  // need to build with older libobjc headers
#if !OBJC_GETCLASSHOOK_DEFINED
  using objc_hook_getClass =  BOOL(*)(const char * _Nonnull name,
                                      Class _Nullable * _Nonnull outClass);
  auto objc_setHook_getClass =
    (void(*)(objc_hook_getClass _Nonnull,
             objc_hook_getClass _Nullable * _Nonnull))
    dlsym(RTLD_DEFAULT, "objc_setHook_getClass");
#endif

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunguarded-availability"
  if (objc_setHook_getClass) {
    objc_setHook_getClass(getObjCClassByMangledName_untrusted,
                          &OldGetClassHook);
  }
#pragma clang diagnostic pop
}