我无法理解内联汇编程序存在的一些问题。
我有一个内联汇编程序的函数。在ASM块内部，我需要使用一些临时寄存器来修改某些系统值。
void setHW(uint32_t val) {
asm volatile (
mrc 15, 0, r0, ...
orr r0, r0, %0
mcr 15, 0, r0, ...
: :"r"(val) :"r0"
);
}
实际上函数是由编译器内联的，没关系，代码仍然运行良好。
当我尝试用一些存根变量替换硬编码的r0时出现问题，因此编译器可以选择最好的寄存器来使用。看起来像这样
void setHW(uint32_t val) {
uint32_t reg;
asm volatile (
mrc 15, 0, %[reg], ...
orr %[reg], %[reg], %0
mcr 15, 0, %[reg], ...
:[reg]"=r"(reg) :"r"(val) :
);
}
现在编译器自己选择注册，但实际上会破坏setHW调用函数的值。
在反汇编程序中它看起来像
add r2, r4, r5 ; caller part, r2 contain some intermedia result
mrc 15, 0, r2, ... ; inlined setHW(), r2 is choosen as scratch reg
orr r2, r2, r0
mcr 15, 0, r2, ...
; caller continue
正如您所看到的，r2已损坏且一切都崩溃了。
如何定义临时寄存器以避免这种情况？
答案 0 :(得分：4)
这样的事情怎么样：
&请注意 @Controller
@SessionAttributes("name")
public class LoginController {
@RequestMapping(value = "/login", method = RequestMethod.POST)
public String handleUserLogin(ModelMap model, @RequestParam String name) {
model.addAttribute("name", name);
return "login";
}
}
以修复早期的clobber问题（有关public class Tutorial1Activity extends Activity implements CvCameraViewListener2 {
private static final String TAG = "OCVSample::Activity";
private CameraBridgeViewBase mOpenCvCameraView;
private boolean mIsJavaCamera = true;
private MenuItem mItemSwitchCamera = null;
//*****************writetoSD***********************//
public FileWriter fw; // = new FileWriter(folder_path, false);
public BufferedWriter bw;// = new BufferedWriter(fw);
boolean first_in = true;
String showTimefile = null;
String showTime = null;
String folder_path = Environment.getExternalStorageDirectory().getAbsolutePath();
String folder_name = "Face Detection Signal";
String folder_pathforfile = null;
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd HH_mm_ss");
SimpleDateFormat sdf_fileintxt = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
//*****************writetoSD***********************//
//---------------MediaRecorder-------------------//
public MediaRecorder mediaRecorder;
Button bt_Record;
boolean isRecord = false;
Handler mThreadHandler;
HandlerThread mHandlerThread;
//---------------MediaRecorder-------------------//
private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
@Override
public void onManagerConnected(int status) {
switch (status) {
case LoaderCallbackInterface.SUCCESS:
{
Log.i(TAG, "OpenCV loaded successfully");
mOpenCvCameraView.enableView();
} break;
default:
{
super.onManagerConnected(status);
} break;
}
}
};
public Tutorial1Activity() {
Log.i(TAG, "Instantiated new " + this.getClass());
}
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
Log.i(TAG, "called onCreate");
super.onCreate(savedInstanceState);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
setContentView(R.layout.tutorial1_surface_view);
mOpenCvCameraView = (CameraBridgeViewBase) findViewById(R.id.tutorial1_activity_java_surface_view);
mOpenCvCameraView.setVisibility(SurfaceView.VISIBLE);
mOpenCvCameraView.setCvCameraViewListener(this);
//---------------------------------------------------------//
bt_Record = (Button)findViewById(R.id.bt_recorder);
folder_pathforfile = folder_path + File.separator + folder_name
+ File.separator + "opencv" + "_";
CreateSDfolder();
ongetTime();
//---------------------------------------------------------//
}
@Override
public void onPause()
{
super.onPause();
if (mOpenCvCameraView != null)
mOpenCvCameraView.disableView();
}
@Override
public void onResume()
{
super.onResume();
if (!OpenCVLoader.initDebug()) {
Log.d(TAG, "Internal OpenCV library not found. Using OpenCV Manager for initialization");
OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_0_0, this, mLoaderCallback);
} else {
Log.d(TAG, "OpenCV library found inside package. Using it!");
mLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS);
}
}
public void onDestroy() {
super.onDestroy();
if (mOpenCvCameraView != null)
mOpenCvCameraView.disableView();
}
public void onCameraViewStarted(int width, int height) {
}
public void onCameraViewStopped() {
}
public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
return inputFrame.rgba();
}
private void CreateSDfolder() {
String filefolderpath = folder_path + File.separator + folder_name;
File dir = new File(filefolderpath);
if (!dir.exists()){
Log.e("folder", "not exist");
try{
//dir.createNewFile(true);
dir.mkdir();
Log.e("folder", "creat exist");
}catch(Exception e){
Log.e("folder", "creat not exist");
e.printStackTrace();
}
}
else{
Log.e("folder", "exist");
}
}
private void ongetTime() {
Date dt=new Date();
showTime=sdf_fileintxt.format(dt);
showTimefile =sdf.format(dt);
}
private void WritetoSD(String data) {
try {
fw = new FileWriter(folder_pathforfile + showTimefile+".txt", true);
bw = new BufferedWriter(fw);
if (first_in == true) {
first_in = false;
bw.append(showTime);
bw.newLine();
}
bw.append(data);
bw.newLine();
bw.flush();
bw.close();
} catch (IOException e) {
Log.e("WriteToSD", "Write To SD ERROR");
e.printStackTrace();
}
}
public void onRecordSignal (View v){
if(!isRecord){
isRecord = true;
Log.e(TAG, "button click " + isRecord);
bt_Record.setText("Stop");
//new MediaPrepareTask().execute(null, null, null);
if (prepareMediaRecorder()) {
// Camera is available and unlocked, MediaRecorder is prepared,
// now you can start recording
Log.e("debug_mediarecorder", "prepareMediaRecorder in if");
mOpenCvCameraView.setRecorder(mediaRecorder);
mediaRecorder.start();
} else {
// prepare didn't work, release the camera
Log.e("debug_mediarecorder", "prepareMediaRecorder in else");
// mediaRecorder.stop();
releaseMediaRecorder();
}
} else{
isRecord = false;
Log.e(TAG, "button click " + isRecord);
bt_Record.setText("Record");
try {
if(mediaRecorder != null)
mediaRecorder.stop(); // stop the recording
else
Log.e(TAG,"onRecordSignal mediaRecorder is null");
} catch (RuntimeException e) {
// RuntimeException is thrown when stop() is called immediately after start().
// In this case the output file is not properly constructed ans should be deleted.
Log.d(TAG, "RuntimeException: stop() is called immediately after start()");
//noinspection ResultOfMethodCallIgnored
}
releaseMediaRecorder(); // release the MediaRecorder object
}
}
public void releaseMediaRecorder() {
Log.e("debug","releaseMediaRecorder");
if (mediaRecorder != null) {
mediaRecorder.reset(); // clear recorder configuration
mediaRecorder.release(); // release the recorder object
mediaRecorder = null;
JavaCameraView.mCamera.lock();
mOpenCvCameraView.releaseRecord();
}
}
private String recordfilepath() {
// TODO Auto-generated method stub
ongetTime();
File sddir = Environment.getExternalStorageDirectory();
File vrdir = new File(sddir, folder_name);
File file = new File(vrdir, showTimefile+"_.mp4");
String filepath = file.getAbsolutePath();
Log.e("debug mediarecorder", filepath);
return filepath;
}
public boolean prepareMediaRecorder() {
// TODO Auto-generated method stub
Log.e("debug mediarecorder", "in prepareMediaRecorder");
mediaRecorder = new MediaRecorder();
try {
JavaCameraView.mCamera.lock();
JavaCameraView.mCamera.unlock();
}catch (RuntimeException e){
Log.e("debug mediarecorder","JavaCameraView.mCamera.unlock() fail");
}
/*mediaRecorder.reset();
mediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
mediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
mediaRecorder.setProfile(CamcorderProfile.get(CamcorderProfile.QUALITY_HIGH));
//mediaRecorder.setPreviewDisplay(CameraBridgeViewBase.mSurfaceHolder.getSurface());
mediaRecorder.setOutputFile(recordfilepath());
//mediaRecorder.setOnInfoListener((MediaRecorder.OnInfoListener) this);
//mediaRecorder.setOnErrorListener((MediaRecorder.OnErrorListener) this);*/
mediaRecorder.reset();
mediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
mediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
CamcorderProfile cpHigh = CamcorderProfile.get(CamcorderProfile.QUALITY_HIGH);
mediaRecorder.setProfile(cpHigh);
//mediaRecorder.setOutputFile("out.mp4");
mediaRecorder.setOutputFile(recordfilepath());
mediaRecorder.setVideoSize(mOpenCvCameraView.mFrameWidth, mOpenCvCameraView.mFrameHeight);
//mediaRecorder.setOnInfoListener(this);
//mediaRecorder.setOnErrorListener(this);
try {
mediaRecorder.prepare();
} catch (IllegalStateException e) {
Log.e("debug mediarecorder", "not prepare");
releaseMediaRecorder();
return false;
} catch (IOException e) {
Log.e("debug mediarecorder", "not prepare IOException");
//releaseMediaRecorder();
}
return true;
}
}
的说明，请参阅https://gcc.gnu.org/onlinedocs/gcc/Modifiers.html。）