A supervisor call instruction, also known as a supervisor call or SVC, is a specific type of machine instruction in computer programming and architecture. It is designed to transfer control from a user program to the operating system or supervisor mode, which has higher privileges and access to system resources.
The supervisor call instruction acts as a gateway for user programs to make requests for services from the operating system. When a program encounters the supervisor call instruction, it triggers a context switch to the operating system, enabling it to execute privileged operations or handle critical tasks on behalf of the user program.
The supervisor call instruction allows the user program to pass parameters or arguments to the operating system, specifying the requested service and providing any necessary data. This information is typically passed through processor registers or memory locations so that the operating system can understand and process the user program's request appropriately.
Upon receiving a supervisor call, the operating system mode takes over, performs the requested service, and may modify the system state or return results back to the user program as needed. Once the service is completed, control is transferred back to the user program, typically to the instruction immediately following the supervisor call instruction.
Supervisor call instructions are crucial for interacting with the operating system, enabling user programs to access system resources, such as file I/O, memory management, interrupt handling, and other privileged operations. They provide a secure and controlled means for user programs to request and utilize the services provided by the operating system, facilitating efficient and safe execution within a computer system.
