2.1代码位置：
frameworks/policies/base/phone/com/android/internal/policy/impl/PhoneWindowManager.java
收索SAFE MODE 这个tag会看到相关代码。
现分析如下：
步骤：在开机动画时，按住MENU键（或者字母S键，方向键的中间键，鼠标左键中的一个）直到开机，会进入安全模式。
得到log如下：
I/WindowManager( 101): SAFE MODE ENABLED (menu=1 s=-1 dpad=-1 trackball=-1)
现象：在机器左小脚显示“安全模式”。
源码
2.3版本：frameworks/base/policy/src/com/android/internal/policy/impl/PhoneWindowManager.java
2291 public boolean detectSafeMode() {
2292 try {
2293 int menuState = mWindowManager.getKeycodeState(KeyEvent.KEYCODE_MENU);
2294 int sState = mWindowManager.getKeycodeState(KeyEvent.KEYCODE_S);
2295 int dpadState = mWindowManager.getDPadKeycodeState(KeyEvent.KEYCODE_DPAD_CENTER);
2296 int trackballState = mWindowManager.getTrackballScancodeState(BTN_MOUSE);
2297 mSafeMode = menuState > 0 || sState > 0 || dpadState > 0 || trackballState > 0;
2298 performHapticFeedbackLw(null, mSafeMode
2299 HapticFeedbackConstants.SAFE_MODE_ENABLED
2300 : HapticFeedbackConstants.SAFE_MODE_DISABLED, true);
2301 if (mSafeMode) {
2302 Log.i(TAG, "SAFE MODE ENABLED (menu=" + menuState + " s=" + sState
2303 + " dpad=" + dpadState + " trackball=" + trackballState + ")");
2304 } else {
2305 Log.i(TAG, "SAFE MODE not enabled");
2306 }
2307 return mSafeMode;
2308 } catch (RemoteException e) {
2309 // Doom! (it's also local)
2310 throw new RuntimeException("window manager dead");
2311 }
2312 }
要把safe mode禁止掉，把mSafeMode赋值为false即可。