Android 如何判断CPU是32位还是64位

可以利用三种方式来判断CPU是32位还是64位：

1. 读取Android 的system property ("ro.product.cpu.abilist64")来判断

2. 读取"/proc/cpuinfo"文件的第一行来判断

3. 读取libc.so文件的ELF头部e_indent[]数组，根据数组第e_indent[4]的取值来判断

public static final String CPU_ARCHITECTURE_TYPE_32 = "32";
public static final String CPU_ARCHITECTURE_TYPE_64 = "64";

/** ELF文件头 e_indent[]数组文件类标识索引 */
private static final int EI_CLASS = 4;
/** ELF文件头 e_indent[EI_CLASS]的取值：ELFCLASS32表示32位目标 */
private static final int ELFCLASS32 = 1;
/** ELF文件头 e_indent[EI_CLASS]的取值：ELFCLASS64表示64位目标 */
private static final int ELFCLASS64 = 2;

/** The system property key of CPU arch type */
private static final String CPU_ARCHITECTURE_KEY_64 = "ro.product.cpu.abilist64";

/** The system libc.so file path */
private static final String SYSTEM_LIB_C_PATH = "/system/lib/libc.so";
private static final String SYSTEM_LIB_C_PATH_64 = "/system/lib64/libc.so";
private static final String PROC_CPU_INFO_PATH = "/proc/cpuinfo";

private static boolean LOGENABLE = false;

/**
* Check if the CPU architecture is x86
*/
public static boolean checkIfCPUx86() {
//1. Check CPU architecture: arm or x86
if (getSystemProperty("ro.product.cpu.abi", "arm").contains("x86")) {
//The CPU is x86
return true;
} else {
return false;
}
}

/**
* Get the CPU arch type: x32 or x64
*/
public static String getArchType(Context context) {
if (getSystemProperty(CPU_ARCHITECTURE_KEY_64, "").length() > 0) {
if (LOGENABLE) {
Log.d("###############getSystemProperty","CPU arch is 64bit");
}
return CPU_ARCHITECTURE_TYPE_64;
} else if (isCPUInfo64()) {
return CPU_ARCHITECTURE_TYPE_64;
} else if (isLibc64()) {
return CPU_ARCHITECTURE_TYPE_64;
} else {
if (LOGENABLE) {
Log.d("###############getArchType()","return cpu DEFAULT 32bit!");
}
return CPU_ARCHITECTURE_TYPE_32;
}
}

private static String getSystemProperty(String key, String defaultValue) {
String value = defaultValue;
try {
Class<?> clazz= Class.forName("android.os.SystemProperties");
Method get = clazz.getMethod("get", String.class, String.class);
value = (String)(get.invoke(clazz, key, ""));
} catch (Exception e) {
if (LOGENABLE) {
Log.d("getSystemProperty", "key = " + key + ", error = " + e.getMessage());
}
}

if (LOGENABLE) {
Log.d("getSystemProperty",  key + " = " + value);
}
return value;
}

/**
* Read the first line of "/proc/cpuinfo" file, and check if it is 64 bit.
*/
private static boolean isCPUInfo64() {
File cpuInfo = new File(PROC_CPU_INFO_PATH);
if (cpuInfo != null && cpuInfo.exists()) {
InputStream inputStream = null;
BufferedReader bufferedReader = null;
try {
inputStream = new FileInputStream(cpuInfo);
bufferedReader = new BufferedReader(new InputStreamReader(inputStream), 512);
String line = bufferedReader.readLine();
if (line != null && line.length() > 0 && line.toLowerCase(Locale.US).contains("arch64")) {
if (LOGENABLE) {
Log.d("###############isCPUInfo64()", PROC_CPU_INFO_PATH + " contains is arch64");
}
return true;
} else {
if (LOGENABLE) {
Log.d("###############isCPUInfo64()", PROC_CPU_INFO_PATH + " is not arch64");
}
}
} catch (Throwable t) {
if (LOGENABLE) {
Log.d("###############isCPUInfo64()","read " + PROC_CPU_INFO_PATH + " error = " + t.toString());
}
} finally {
try {
if (bufferedReader != null) {
bufferedReader.close();
}
} catch (Exception e) {
e.printStackTrace();
}

try {
if (inputStream != null) {
inputStream.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
return false;
}

/**
* Check if system libc.so is 32 bit or 64 bit
*/
private static boolean isLibc64() {
File libcFile = new File(SYSTEM_LIB_C_PATH);
if (libcFile != null && libcFile.exists()) {
byte[] header = readELFHeadrIndentArray(libcFile);
if (header != null && header[EI_CLASS] == ELFCLASS64) {
if (LOGENABLE) {
Log.d("###############isLibc64()", SYSTEM_LIB_C_PATH + " is 64bit");
}
return true;
}
}

File libcFile64 = new File(SYSTEM_LIB_C_PATH_64);
if (libcFile64 != null && libcFile64.exists()) {
byte[] header = readELFHeadrIndentArray(libcFile64);
if (header != null && header[EI_CLASS] == ELFCLASS64) {
if (LOGENABLE) {
Log.d("###############isLibc64()", SYSTEM_LIB_C_PATH_64 + " is 64bit");
}
return true;
}
}

return false;
}

/**
* ELF文件头格式是固定的:文件开始是一个16字节的byte数组e_indent[16]
* e_indent[4]的值可以判断ELF是32位还是64位
*/
private static byte[] readELFHeadrIndentArray(File libFile) {
if (libFile != null && libFile.exists()) {
FileInputStream inputStream = null;
try {
inputStream = new FileInputStream(libFile);
if (inputStream != null) {
byte[] tempBuffer = new byte[16];
int count = inputStream.read(tempBuffer, 0, 16);
if (count == 16) {
return tempBuffer;
} else {
if (LOGENABLE) {
Log.e("readELFHeadrIndentArray", "Error: e_indent lenght should be 16, but actual is " +  count);
}
}
}
} catch (Throwable t) {
if (LOGENABLE) {
Log.e("readELFHeadrIndentArray", "Error:" + t.toString());
}
} finally {
if (inputStream != null) {
try {
inputStream.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}

return null;
}