UPPCL AE 2018:45

Question

In which of the following cases, a process executing in user mode requires an entry into the $\text{OS}$ mode?

• A. Decrementing an unsigned integer value stored in a register beyond zero
• B. Adding values of two registers using $\textsf{ADD}$ instruction
• C. Executing $\textsf{printf} ()$
• D. Accessing a general purpose register

Answer 1

printf() call write system call  and that's why an entry required in os/kernel mode