25 votes 25 votes System calls are usually invoked by using a software interrupt polling an indirect jump a privileged instruction Operating System gate1999 operating-system normal ugcnetcse-dec2015-paper2 os-protection + – Kathleen asked Sep 23, 2014 retagged May 26, 2020 by Arjun Kathleen 11.9k views answer comment Share Follow See 1 comment See all 1 1 comment reply Vikrant Singh commented Jan 9, 2015 reply Follow Share Ans A 6 votes 6 votes Please log in or register to add a comment.
Best answer 52 votes 52 votes Software interrupt is the answer. Privileged instruction cannot be the answer as system call is done from user mode and privileged instruction cannot be done from user mode. Arjun answered Apr 16, 2015 selected Dec 3, 2016 by Nishant Arora Arjun comment Share Follow See all 5 Comments See all 5 5 Comments reply Show 2 previous comments Manoja Rajalakshmi A commented Nov 23, 2018 reply Follow Share Note: Implementing system calls requires a transfer of control from user space to kernel space, which involves some sort of architecture-specific feature. A typical way to implement this is to use a software interrupt or trap. Interrupts transfer control to the operating system kernel, so software simply needs to set up some register with the system call number needed, and execute the software interrupt. https://en.wikipedia.org/wiki/System_call#Typical_implementations 8 votes 8 votes Saloni maheshwari commented May 6, 2020 reply Follow Share But in the above answer it is mentioned that system call is implemented from user mode.what is correct?? 0 votes 0 votes KartikGawande commented Nov 2, 2022 reply Follow Share Saloni maheshwari yes the system calls prolly sets the register with the system call number needed so it is executed in user mode but then the interrupt transfers the control to kernel mode. So answer and the above comment are not contradictory to each other. 0 votes 0 votes Please log in or register to add a comment.
15 votes 15 votes Ans) A Software interrupt https://en.wikipedia.org/wiki/System_call#Typical_implementations Prasanna answered Nov 2, 2015 Prasanna comment Share Follow See all 0 reply Please log in or register to add a comment.