Source file missing : boot_serial.c

Thank you for your reply.
However, when I locate all these source files,
the code still can't reach the main (I set a breakpoint in it.)

This is a different issue than the first. If you program has a main and it is unable to reach it, there is some issue with the application that is preventing it. The potential reasons can be numerous, such as a bug in the code or the target has not been initialized correctly.

Is this the same issue you described below in another thread?
e2e.ti.com/.../538569

Yes! This is the same issue I described in the thread below:

Thank you for your reply first, the "source file missing" issue is solved, but I still cannot reach into the main.

"No source available for "0x8805c"  warning message won't show up every time into the debug mode,

However, no matter the warning message shows up or not, the program cannot get into the main.

The code works successfully last week, so I am confused about this issue.

My CCS version is 6.1.2. Thank you :)

The "No source available for "0x8805c" issue has been resolved as per this thread:
https://e2e.ti.com/support/development_tools/code_composer_studio/f/81/p/538569/1965975#1965975