How to map a library to absolute address?

And once it has them, how will that set-up be any more useful than the obvious approach
those libraries provides service functions for user mode. for example, one library may include a function like memcpy(). The approach is not to prevent the user mode from executing those libraries, I'm concerned to prevent the user mode from accessing the other regions.

And once it has them, how will that set-up be any more useful than the obvious approach
those libraries provides service functions for user mode. for example, one library may include a function like memcpy(). The approach is not to prevent the user mode from executing those libraries, I'm concerned to prevent the user mode from accessing the other regions.

I'm concerned to prevent the user mode from accessing the other regions.
Then I suggest you put those other parts of code into a decidated region, which you can configure as system-mode only.

But before you make any further step, you really need to sit down and learn a lot about how the '51 tools work. This is a highly unusual C toolchain, for which a lot of things that would apply cleanly on almost every other system, just don't.