why clear interrput flag cause segmentation fault in C?

Question

I am learning some basics about Assembly and C. for learning purpose I decide to write a simple program that disable Interrupts and when user wants to type something in the console he/she can't :

#include <stdio.h>
int main(){
    int a;
    printf("enter your number : ");
    asm ("cli");
    scanf("%d", &a);
    printf("your number is %d\n" , a);     
    return 0;
}

but when I compile this with GCC I got segmentation fault :

Segmentation fault (core dumped)

And when I debug it with gdb I got this message when program reach to the asm("cli"); line:

Program received signal SIGSEGV, Segmentation fault.
main () at cli.c:6
6       asm ("cli");

Answer 1

This is happening because You can't disable interrupts from user space program. All interrupts are under the control of kernel. You need to do it from kernel space. Before you do it you need to learn kernel internals first and playing with interrupts are very critical and requires more knowledge on kernel according to my knowledge.

You need to write a kernel module that can interact with user space through /dev/ (or some other) interface. User space code should request kernel module to disable interrupts.