made easy test series

Question

Which of the following operations require the executing code to be operating with kernal mode?

A)Performing semaphore 'P' operation.

B)Making system call

C)Disabling interrupt

D)both (B) and (C)

Comments

D ) both B and C

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@ answer given is option C) only

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A program running in user mode can also make system calls. Once it makes such call then mode changes from user to kernel. But for making a system call the program need not be present in the kernel mode.

Eg: While we write a C prog (we are in user mode) for creating a file we write fopen. This is not a system call but this library function which invokes the system call open(). Upon executing this, mode is changed from user to kernel, a file is being created and given to the user.

That is why B is not correct

Answer 1

A doesnt need to be in kernel mode as incrementing variables doesnt cause race condition, B is also wrong as system calls can be made in user mode (which inturn is executed in kernel mode),

 

C is true, because interrupts cant be disabled in user mode.

Comments

nice bro thanks