Final answer:
The callee can avoid overwriting important data by using caller-save and callee-save conventions, where the callee is responsible for saving the contents of certain registers onto the stack and restoring them before returning from the function.
Step-by-step explanation:
When a callee requires registers for local variables and we need to ensure that important data isn't overwritten, a convention known as caller-save and callee-save is used. This concept is a part of calling conventions in computer programming.
Caller-save registers are those where the caller is responsible for saving and restoring the original values if they wish to preserve them across a function call. Conversely, callee-save registers are those where the callee is responsible for saving the contents of the register at the beginning of the function and restoring them before returning.
To prevent data loss, the callee can push the registers' values onto the stack at the start of the function (callee-save), and pop them off to restore the values before the function returns. Furthermore, local variables can also be allocated on the stack rather than in registers to free up registers for other uses. This ensures that all critical data is preserved throughout the function call process.