Undefined Reference to 'fill_cpu': Troubleshooting Guide

This error message typically occurs when the linker cannot find a function definition for the function 'fill_cpu'. This could be due to a few different reasons:

1. The function is not defined in any of the source files that are being compiled.
2. The function is defined in a source file that is not being linked with the rest of the program.
3. The function is defined in a library that is not being linked with the rest of the program.

To resolve this error, you will need to ensure that the function 'fill_cpu' is defined in one of the source files that is being compiled, and that the resulting object file is being linked with the rest of the program. If the function is defined in a library, you will need to ensure that the library is being linked with the rest of the program as well.