compiler-rt/lib/builtins/os_version_check.c - llvm-project - Git at Google

 //===-- os_version_check.c - OS version checking  -------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the function __isOSVersionAtLeast, used by
 // Objective-C's @available
 //
 //===----------------------------------------------------------------------===//

 #ifdef __APPLE__

 #include <TargetConditionals.h>
 #include <dispatch/dispatch.h>
 #include <dlfcn.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 // These three variables hold the host's OS version.
 static int32_t GlobalMajor, GlobalMinor, GlobalSubminor;
 static dispatch_once_t DispatchOnceCounter;
 static dispatch_once_t CompatibilityDispatchOnceCounter;

 // _availability_version_check darwin API support.
 typedef uint32_t dyld_platform_t;

 typedef struct {
   dyld_platform_t platform;
   uint32_t version;
 } dyld_build_version_t;

 typedef bool (*AvailabilityVersionCheckFuncTy)(uint32_t count,
                                                dyld_build_version_t versions[]);

 static AvailabilityVersionCheckFuncTy AvailabilityVersionCheck;

 // We can't include <CoreFoundation/CoreFoundation.h> directly from here, so
 // just forward declare everything that we need from it.

 typedef const void *CFDataRef, *CFAllocatorRef, *CFPropertyListRef,
     *CFStringRef, *CFDictionaryRef, *CFTypeRef, *CFErrorRef;

 #if __LLP64__
 typedef unsigned long long CFTypeID;
 typedef unsigned long long CFOptionFlags;
 typedef signed long long CFIndex;
 #else
 typedef unsigned long CFTypeID;
 typedef unsigned long CFOptionFlags;
 typedef signed long CFIndex;
 #endif

 typedef unsigned char UInt8;
 typedef _Bool Boolean;
 typedef CFIndex CFPropertyListFormat;
 typedef uint32_t CFStringEncoding;

 // kCFStringEncodingASCII analog.
 #define CF_STRING_ENCODING_ASCII 0x0600
 // kCFStringEncodingUTF8 analog.
 #define CF_STRING_ENCODING_UTF8 0x08000100
 #define CF_PROPERTY_LIST_IMMUTABLE 0

 typedef CFDataRef (*CFDataCreateWithBytesNoCopyFuncTy)(CFAllocatorRef,
                                                        const UInt8 *, CFIndex,
                                                        CFAllocatorRef);
 typedef CFPropertyListRef (*CFPropertyListCreateWithDataFuncTy)(
     CFAllocatorRef, CFDataRef, CFOptionFlags, CFPropertyListFormat *,
     CFErrorRef *);
 typedef CFPropertyListRef (*CFPropertyListCreateFromXMLDataFuncTy)(
     CFAllocatorRef, CFDataRef, CFOptionFlags, CFStringRef *);
 typedef CFStringRef (*CFStringCreateWithCStringNoCopyFuncTy)(CFAllocatorRef,
                                                              const char *,
                                                              CFStringEncoding,
                                                              CFAllocatorRef);
 typedef const void *(*CFDictionaryGetValueFuncTy)(CFDictionaryRef,
                                                   const void *);
 typedef CFTypeID (*CFGetTypeIDFuncTy)(CFTypeRef);
 typedef CFTypeID (*CFStringGetTypeIDFuncTy)(void);
 typedef Boolean (*CFStringGetCStringFuncTy)(CFStringRef, char *, CFIndex,
                                             CFStringEncoding);
 typedef void (*CFReleaseFuncTy)(CFTypeRef);

 static void _initializeAvailabilityCheck(bool LoadPlist) {
   if (AvailabilityVersionCheck && !LoadPlist) {
     // New API is supported and we're not being asked to load the plist,
     // exit early!
     return;
   }

   // Use the new API if it's is available.
   AvailabilityVersionCheck = (AvailabilityVersionCheckFuncTy)dlsym(
       RTLD_DEFAULT, "_availability_version_check");

   if (AvailabilityVersionCheck && !LoadPlist) {
     // New API is supported and we're not being asked to load the plist,
     // exit early!
     return;
   }
   // Still load the PLIST to ensure that the existing calls to
   // __isOSVersionAtLeast still work even with new compiler-rt and old OSes.

   // Load CoreFoundation dynamically
   const void *NullAllocator = dlsym(RTLD_DEFAULT, "kCFAllocatorNull");
   if (!NullAllocator)
     return;
   const CFAllocatorRef AllocatorNull = *(const CFAllocatorRef *)NullAllocator;
   CFDataCreateWithBytesNoCopyFuncTy CFDataCreateWithBytesNoCopyFunc =
       (CFDataCreateWithBytesNoCopyFuncTy)dlsym(RTLD_DEFAULT,
                                                "CFDataCreateWithBytesNoCopy");
   if (!CFDataCreateWithBytesNoCopyFunc)
     return;
   CFPropertyListCreateWithDataFuncTy CFPropertyListCreateWithDataFunc =
       (CFPropertyListCreateWithDataFuncTy)dlsym(RTLD_DEFAULT,
                                                 "CFPropertyListCreateWithData");
 // CFPropertyListCreateWithData was introduced only in macOS 10.6+, so it
 // will be NULL on earlier OS versions.
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
   CFPropertyListCreateFromXMLDataFuncTy CFPropertyListCreateFromXMLDataFunc =
       (CFPropertyListCreateFromXMLDataFuncTy)dlsym(
           RTLD_DEFAULT, "CFPropertyListCreateFromXMLData");
 #pragma clang diagnostic pop
   // CFPropertyListCreateFromXMLDataFunc is deprecated in macOS 10.10, so it
   // might be NULL in future OS versions.
   if (!CFPropertyListCreateWithDataFunc && !CFPropertyListCreateFromXMLDataFunc)
     return;
   CFStringCreateWithCStringNoCopyFuncTy CFStringCreateWithCStringNoCopyFunc =
       (CFStringCreateWithCStringNoCopyFuncTy)dlsym(
           RTLD_DEFAULT, "CFStringCreateWithCStringNoCopy");
   if (!CFStringCreateWithCStringNoCopyFunc)
     return;
   CFDictionaryGetValueFuncTy CFDictionaryGetValueFunc =
       (CFDictionaryGetValueFuncTy)dlsym(RTLD_DEFAULT, "CFDictionaryGetValue");
   if (!CFDictionaryGetValueFunc)
     return;
   CFGetTypeIDFuncTy CFGetTypeIDFunc =
       (CFGetTypeIDFuncTy)dlsym(RTLD_DEFAULT, "CFGetTypeID");
   if (!CFGetTypeIDFunc)
     return;
   CFStringGetTypeIDFuncTy CFStringGetTypeIDFunc =
       (CFStringGetTypeIDFuncTy)dlsym(RTLD_DEFAULT, "CFStringGetTypeID");
   if (!CFStringGetTypeIDFunc)
     return;
   CFStringGetCStringFuncTy CFStringGetCStringFunc =
       (CFStringGetCStringFuncTy)dlsym(RTLD_DEFAULT, "CFStringGetCString");
   if (!CFStringGetCStringFunc)
     return;
   CFReleaseFuncTy CFReleaseFunc =
       (CFReleaseFuncTy)dlsym(RTLD_DEFAULT, "CFRelease");
   if (!CFReleaseFunc)
     return;

   char *PListPath = "/System/Library/CoreServices/SystemVersion.plist";

 #if TARGET_OS_SIMULATOR
   char *PListPathPrefix = getenv("IPHONE_SIMULATOR_ROOT");
   if (!PListPathPrefix)
     return;
   char FullPath[strlen(PListPathPrefix) + strlen(PListPath) + 1];
   strcpy(FullPath, PListPathPrefix);
   strcat(FullPath, PListPath);
   PListPath = FullPath;
 #endif
   FILE *PropertyList = fopen(PListPath, "r");
   if (!PropertyList)
     return;

   // Dynamically allocated stuff.
   CFDictionaryRef PListRef = NULL;
   CFDataRef FileContentsRef = NULL;
   UInt8 *PListBuf = NULL;

   fseek(PropertyList, 0, SEEK_END);
   long PListFileSize = ftell(PropertyList);
   if (PListFileSize < 0)
     goto Fail;
   rewind(PropertyList);

   PListBuf = malloc((size_t)PListFileSize);
   if (!PListBuf)
     goto Fail;

   size_t NumRead = fread(PListBuf, 1, (size_t)PListFileSize, PropertyList);
   if (NumRead != (size_t)PListFileSize)
     goto Fail;

   // Get the file buffer into CF's format. We pass in a null allocator here *
   // because we free PListBuf ourselves
   FileContentsRef = (*CFDataCreateWithBytesNoCopyFunc)(
       NULL, PListBuf, (CFIndex)NumRead, AllocatorNull);
   if (!FileContentsRef)
     goto Fail;

   if (CFPropertyListCreateWithDataFunc)
     PListRef = (*CFPropertyListCreateWithDataFunc)(
         NULL, FileContentsRef, CF_PROPERTY_LIST_IMMUTABLE, NULL, NULL);
   else
     PListRef = (*CFPropertyListCreateFromXMLDataFunc)(
         NULL, FileContentsRef, CF_PROPERTY_LIST_IMMUTABLE, NULL);
   if (!PListRef)
     goto Fail;

   CFStringRef ProductVersion = (*CFStringCreateWithCStringNoCopyFunc)(
       NULL, "ProductVersion", CF_STRING_ENCODING_ASCII, AllocatorNull);
   if (!ProductVersion)
     goto Fail;
   CFTypeRef OpaqueValue = (*CFDictionaryGetValueFunc)(PListRef, ProductVersion);
   (*CFReleaseFunc)(ProductVersion);
   if (!OpaqueValue ||
       (*CFGetTypeIDFunc)(OpaqueValue) != (*CFStringGetTypeIDFunc)())
     goto Fail;

   char VersionStr[32];
   if (!(*CFStringGetCStringFunc)((CFStringRef)OpaqueValue, VersionStr,
                                  sizeof(VersionStr), CF_STRING_ENCODING_UTF8))
     goto Fail;
   sscanf(VersionStr, "%d.%d.%d", &GlobalMajor, &GlobalMinor, &GlobalSubminor);

 Fail:
   if (PListRef)
     (*CFReleaseFunc)(PListRef);
   if (FileContentsRef)
     (*CFReleaseFunc)(FileContentsRef);
   free(PListBuf);
   fclose(PropertyList);
 }

 // Find and parse the SystemVersion.plist file.
 static void compatibilityInitializeAvailabilityCheck(void *Unused) {
   (void)Unused;
   _initializeAvailabilityCheck(/*LoadPlist=*/true);
 }

 static void initializeAvailabilityCheck(void *Unused) {
   (void)Unused;
   _initializeAvailabilityCheck(/*LoadPlist=*/false);
 }

 // This old API entry point is no longer used by Clang for Darwin. We still need
 // to keep it around to ensure that object files that reference it are still
 // usable when linked with new compiler-rt.
 int32_t __isOSVersionAtLeast(int32_t Major, int32_t Minor, int32_t Subminor) {
   // Populate the global version variables, if they haven't already.
   dispatch_once_f(&CompatibilityDispatchOnceCounter, NULL,
                   compatibilityInitializeAvailabilityCheck);

   if (Major < GlobalMajor)
     return 1;
   if (Major > GlobalMajor)
     return 0;
   if (Minor < GlobalMinor)
     return 1;
   if (Minor > GlobalMinor)
     return 0;
   return Subminor <= GlobalSubminor;
 }

 static inline uint32_t ConstructVersion(uint32_t Major, uint32_t Minor,
                                         uint32_t Subminor) {
   return ((Major & 0xffff) << 16) | ((Minor & 0xff) << 8) | (Subminor & 0xff);
 }

 int32_t __isPlatformVersionAtLeast(uint32_t Platform, uint32_t Major,
                                    uint32_t Minor, uint32_t Subminor) {
   dispatch_once_f(&DispatchOnceCounter, NULL, initializeAvailabilityCheck);

   if (!AvailabilityVersionCheck) {
     return __isOSVersionAtLeast(Major, Minor, Subminor);
   }
   dyld_build_version_t Versions[] = {
       {Platform, ConstructVersion(Major, Minor, Subminor)}};
   return AvailabilityVersionCheck(1, Versions);
 }

 #elif __ANDROID__

 #include <pthread.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/system_properties.h>

 static int SdkVersion;
 static int IsPreRelease;

 static void readSystemProperties(void) {
   char buf[PROP_VALUE_MAX];

   if (__system_property_get("ro.build.version.sdk", buf) == 0) {
     // When the system property doesn't exist, defaults to future API level.
     SdkVersion = __ANDROID_API_FUTURE__;
   } else {
     SdkVersion = atoi(buf);
   }

   if (__system_property_get("ro.build.version.codename", buf) == 0) {
     IsPreRelease = 1;
   } else {
     IsPreRelease = strcmp(buf, "REL") != 0;
   }
   return;
 }

 int32_t __isOSVersionAtLeast(int32_t Major, int32_t Minor, int32_t Subminor) {
   (int32_t) Minor;
   (int32_t) Subminor;
   static pthread_once_t once = PTHREAD_ONCE_INIT;
   pthread_once(&once, readSystemProperties);

   return SdkVersion >= Major ||
          (IsPreRelease && Major == __ANDROID_API_FUTURE__);
 }

 #else

 // Silence an empty translation unit warning.
 typedef int unused;

 #endif
	//===-- os_version_check.c - OS version checking -------------------------===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//
	//
	// This file implements the function __isOSVersionAtLeast, used by
	// Objective-C's @available
	//
	//===----------------------------------------------------------------------===//

	#ifdef __APPLE__

	#include <TargetConditionals.h>
	#include <dispatch/dispatch.h>
	#include <dlfcn.h>
	#include <stdint.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>

	// These three variables hold the host's OS version.
	static int32_t GlobalMajor, GlobalMinor, GlobalSubminor;
	static dispatch_once_t DispatchOnceCounter;
	static dispatch_once_t CompatibilityDispatchOnceCounter;

	// _availability_version_check darwin API support.
	typedef uint32_t dyld_platform_t;

	typedef struct {
	dyld_platform_t platform;
	uint32_t version;
	} dyld_build_version_t;

	typedef bool (*AvailabilityVersionCheckFuncTy)(uint32_t count,
	dyld_build_version_t versions[]);

	static AvailabilityVersionCheckFuncTy AvailabilityVersionCheck;

	// We can't include <CoreFoundation/CoreFoundation.h> directly from here, so
	// just forward declare everything that we need from it.

	typedef const void CFDataRef, CFAllocatorRef, *CFPropertyListRef,
	CFStringRef, CFDictionaryRef, CFTypeRef, CFErrorRef;

	#if __LLP64__
	typedef unsigned long long CFTypeID;
	typedef unsigned long long CFOptionFlags;
	typedef signed long long CFIndex;
	#else
	typedef unsigned long CFTypeID;
	typedef unsigned long CFOptionFlags;
	typedef signed long CFIndex;
	#endif

	typedef unsigned char UInt8;
	typedef _Bool Boolean;
	typedef CFIndex CFPropertyListFormat;
	typedef uint32_t CFStringEncoding;

	// kCFStringEncodingASCII analog.
	#define CF_STRING_ENCODING_ASCII 0x0600
	// kCFStringEncodingUTF8 analog.
	#define CF_STRING_ENCODING_UTF8 0x08000100
	#define CF_PROPERTY_LIST_IMMUTABLE 0

	typedef CFDataRef (*CFDataCreateWithBytesNoCopyFuncTy)(CFAllocatorRef,
	const UInt8 *, CFIndex,
	CFAllocatorRef);
	typedef CFPropertyListRef (*CFPropertyListCreateWithDataFuncTy)(
	CFAllocatorRef, CFDataRef, CFOptionFlags, CFPropertyListFormat *,
	CFErrorRef *);
	typedef CFPropertyListRef (*CFPropertyListCreateFromXMLDataFuncTy)(
	CFAllocatorRef, CFDataRef, CFOptionFlags, CFStringRef *);
	typedef CFStringRef (*CFStringCreateWithCStringNoCopyFuncTy)(CFAllocatorRef,
	const char *,
	CFStringEncoding,
	CFAllocatorRef);
	typedef const void (CFDictionaryGetValueFuncTy)(CFDictionaryRef,
	const void *);
	typedef CFTypeID (*CFGetTypeIDFuncTy)(CFTypeRef);
	typedef CFTypeID (*CFStringGetTypeIDFuncTy)(void);
	typedef Boolean (CFStringGetCStringFuncTy)(CFStringRef, char , CFIndex,
	CFStringEncoding);
	typedef void (*CFReleaseFuncTy)(CFTypeRef);

	static void _initializeAvailabilityCheck(bool LoadPlist) {
	if (AvailabilityVersionCheck && !LoadPlist) {
	// New API is supported and we're not being asked to load the plist,
	// exit early!
	return;
	}

	// Use the new API if it's is available.
	AvailabilityVersionCheck = (AvailabilityVersionCheckFuncTy)dlsym(
	RTLD_DEFAULT, "_availability_version_check");

	if (AvailabilityVersionCheck && !LoadPlist) {
	// New API is supported and we're not being asked to load the plist,
	// exit early!
	return;
	}
	// Still load the PLIST to ensure that the existing calls to
	// __isOSVersionAtLeast still work even with new compiler-rt and old OSes.

	// Load CoreFoundation dynamically
	const void *NullAllocator = dlsym(RTLD_DEFAULT, "kCFAllocatorNull");
	if (!NullAllocator)
	return;
	const CFAllocatorRef AllocatorNull = (const CFAllocatorRef )NullAllocator;
	CFDataCreateWithBytesNoCopyFuncTy CFDataCreateWithBytesNoCopyFunc =
	(CFDataCreateWithBytesNoCopyFuncTy)dlsym(RTLD_DEFAULT,
	"CFDataCreateWithBytesNoCopy");
	if (!CFDataCreateWithBytesNoCopyFunc)
	return;
	CFPropertyListCreateWithDataFuncTy CFPropertyListCreateWithDataFunc =
	(CFPropertyListCreateWithDataFuncTy)dlsym(RTLD_DEFAULT,
	"CFPropertyListCreateWithData");
	// CFPropertyListCreateWithData was introduced only in macOS 10.6+, so it
	// will be NULL on earlier OS versions.
	#pragma clang diagnostic push
	#pragma clang diagnostic ignored "-Wdeprecated-declarations"
	CFPropertyListCreateFromXMLDataFuncTy CFPropertyListCreateFromXMLDataFunc =
	(CFPropertyListCreateFromXMLDataFuncTy)dlsym(
	RTLD_DEFAULT, "CFPropertyListCreateFromXMLData");
	#pragma clang diagnostic pop
	// CFPropertyListCreateFromXMLDataFunc is deprecated in macOS 10.10, so it
	// might be NULL in future OS versions.
	if (!CFPropertyListCreateWithDataFunc && !CFPropertyListCreateFromXMLDataFunc)
	return;
	CFStringCreateWithCStringNoCopyFuncTy CFStringCreateWithCStringNoCopyFunc =
	(CFStringCreateWithCStringNoCopyFuncTy)dlsym(
	RTLD_DEFAULT, "CFStringCreateWithCStringNoCopy");
	if (!CFStringCreateWithCStringNoCopyFunc)
	return;
	CFDictionaryGetValueFuncTy CFDictionaryGetValueFunc =
	(CFDictionaryGetValueFuncTy)dlsym(RTLD_DEFAULT, "CFDictionaryGetValue");
	if (!CFDictionaryGetValueFunc)
	return;
	CFGetTypeIDFuncTy CFGetTypeIDFunc =
	(CFGetTypeIDFuncTy)dlsym(RTLD_DEFAULT, "CFGetTypeID");
	if (!CFGetTypeIDFunc)
	return;
	CFStringGetTypeIDFuncTy CFStringGetTypeIDFunc =
	(CFStringGetTypeIDFuncTy)dlsym(RTLD_DEFAULT, "CFStringGetTypeID");
	if (!CFStringGetTypeIDFunc)
	return;
	CFStringGetCStringFuncTy CFStringGetCStringFunc =
	(CFStringGetCStringFuncTy)dlsym(RTLD_DEFAULT, "CFStringGetCString");
	if (!CFStringGetCStringFunc)
	return;
	CFReleaseFuncTy CFReleaseFunc =
	(CFReleaseFuncTy)dlsym(RTLD_DEFAULT, "CFRelease");
	if (!CFReleaseFunc)
	return;

	char *PListPath = "/System/Library/CoreServices/SystemVersion.plist";

	#if TARGET_OS_SIMULATOR
	char *PListPathPrefix = getenv("IPHONE_SIMULATOR_ROOT");
	if (!PListPathPrefix)
	return;
	char FullPath[strlen(PListPathPrefix) + strlen(PListPath) + 1];
	strcpy(FullPath, PListPathPrefix);
	strcat(FullPath, PListPath);
	PListPath = FullPath;
	#endif
	FILE *PropertyList = fopen(PListPath, "r");
	if (!PropertyList)
	return;

	// Dynamically allocated stuff.
	CFDictionaryRef PListRef = NULL;
	CFDataRef FileContentsRef = NULL;
	UInt8 *PListBuf = NULL;

	fseek(PropertyList, 0, SEEK_END);
	long PListFileSize = ftell(PropertyList);
	if (PListFileSize < 0)
	goto Fail;
	rewind(PropertyList);

	PListBuf = malloc((size_t)PListFileSize);
	if (!PListBuf)
	goto Fail;

	size_t NumRead = fread(PListBuf, 1, (size_t)PListFileSize, PropertyList);
	if (NumRead != (size_t)PListFileSize)
	goto Fail;

	// Get the file buffer into CF's format. We pass in a null allocator here *
	// because we free PListBuf ourselves
	FileContentsRef = (*CFDataCreateWithBytesNoCopyFunc)(
	NULL, PListBuf, (CFIndex)NumRead, AllocatorNull);
	if (!FileContentsRef)
	goto Fail;

	if (CFPropertyListCreateWithDataFunc)
	PListRef = (*CFPropertyListCreateWithDataFunc)(
	NULL, FileContentsRef, CF_PROPERTY_LIST_IMMUTABLE, NULL, NULL);
	else
	PListRef = (*CFPropertyListCreateFromXMLDataFunc)(
	NULL, FileContentsRef, CF_PROPERTY_LIST_IMMUTABLE, NULL);
	if (!PListRef)
	goto Fail;

	CFStringRef ProductVersion = (*CFStringCreateWithCStringNoCopyFunc)(
	NULL, "ProductVersion", CF_STRING_ENCODING_ASCII, AllocatorNull);
	if (!ProductVersion)
	goto Fail;
	CFTypeRef OpaqueValue = (*CFDictionaryGetValueFunc)(PListRef, ProductVersion);
	(*CFReleaseFunc)(ProductVersion);
	if (!OpaqueValue \|\|
	(CFGetTypeIDFunc)(OpaqueValue) != (CFStringGetTypeIDFunc)())
	goto Fail;

	char VersionStr[32];
	if (!(*CFStringGetCStringFunc)((CFStringRef)OpaqueValue, VersionStr,
	sizeof(VersionStr), CF_STRING_ENCODING_UTF8))
	goto Fail;
	sscanf(VersionStr, "%d.%d.%d", &GlobalMajor, &GlobalMinor, &GlobalSubminor);

	Fail:
	if (PListRef)
	(*CFReleaseFunc)(PListRef);
	if (FileContentsRef)
	(*CFReleaseFunc)(FileContentsRef);
	free(PListBuf);
	fclose(PropertyList);
	}

	// Find and parse the SystemVersion.plist file.
	static void compatibilityInitializeAvailabilityCheck(void *Unused) {
	(void)Unused;
	_initializeAvailabilityCheck(/LoadPlist=/true);
	}

	static void initializeAvailabilityCheck(void *Unused) {
	(void)Unused;
	_initializeAvailabilityCheck(/LoadPlist=/false);
	}

	// This old API entry point is no longer used by Clang for Darwin. We still need
	// to keep it around to ensure that object files that reference it are still
	// usable when linked with new compiler-rt.
	int32_t __isOSVersionAtLeast(int32_t Major, int32_t Minor, int32_t Subminor) {
	// Populate the global version variables, if they haven't already.
	dispatch_once_f(&CompatibilityDispatchOnceCounter, NULL,
	compatibilityInitializeAvailabilityCheck);

	if (Major < GlobalMajor)
	return 1;
	if (Major > GlobalMajor)
	return 0;
	if (Minor < GlobalMinor)
	return 1;
	if (Minor > GlobalMinor)
	return 0;
	return Subminor <= GlobalSubminor;
	}

	static inline uint32_t ConstructVersion(uint32_t Major, uint32_t Minor,
	uint32_t Subminor) {
	return ((Major & 0xffff) << 16) \| ((Minor & 0xff) << 8) \| (Subminor & 0xff);
	}

	int32_t __isPlatformVersionAtLeast(uint32_t Platform, uint32_t Major,
	uint32_t Minor, uint32_t Subminor) {
	dispatch_once_f(&DispatchOnceCounter, NULL, initializeAvailabilityCheck);

	if (!AvailabilityVersionCheck) {
	return __isOSVersionAtLeast(Major, Minor, Subminor);
	}
	dyld_build_version_t Versions[] = {
	{Platform, ConstructVersion(Major, Minor, Subminor)}};
	return AvailabilityVersionCheck(1, Versions);
	}

	#elif __ANDROID__

	#include <pthread.h>
	#include <stdlib.h>
	#include <string.h>
	#include <sys/system_properties.h>

	static int SdkVersion;
	static int IsPreRelease;

	static void readSystemProperties(void) {
	char buf[PROP_VALUE_MAX];

	if (__system_property_get("ro.build.version.sdk", buf) == 0) {
	// When the system property doesn't exist, defaults to future API level.
	SdkVersion = __ANDROID_API_FUTURE__;
	} else {
	SdkVersion = atoi(buf);
	}

	if (__system_property_get("ro.build.version.codename", buf) == 0) {
	IsPreRelease = 1;
	} else {
	IsPreRelease = strcmp(buf, "REL") != 0;
	}
	return;
	}

	int32_t __isOSVersionAtLeast(int32_t Major, int32_t Minor, int32_t Subminor) {
	(int32_t) Minor;
	(int32_t) Subminor;
	static pthread_once_t once = PTHREAD_ONCE_INIT;
	pthread_once(&once, readSystemProperties);

	return SdkVersion >= Major \|\|
	(IsPreRelease && Major == __ANDROID_API_FUTURE__);
	}

	#else

	// Silence an empty translation unit warning.
	typedef int unused;

	#endif