Is the execution of kernel code for handling a system call from a process considered part of the process?

Question

(I am mainly asking the following OS questions from computer science point of view. In the following, if I need to be specific about the OS, I am mainly talking about linux)

A process is defined as an execution of one or more programs.

Yet we often distinguish between user programs and an OS kernel (which also consists of programs).

• Does a process only execute user programs, not programs in an OS kernel?

• When a process issues a system call, the cpu then switches from user mode to kernel mode and executes the system call handler in the kernel code. Is the execution of the system call handler (as part of the kernel code) part of the process, or is it part of the execution of the OS kernel?

Thanks.

Answer 1

In most operating systems, the "kernel" executes in the context of a process. There are some that work differently but this is the general mechanism use. A process switches between user mode and kernel mode (and some systems have additional modes).

Does a process only execute user programs, not programs in an OS kernel?

There are no programs in an OS kernel (generally). A process can execute interrupt and exception handlers in kernel mode.

When a process issues a system call, the cpu then switches from user mode to kernel mode and executes the system call handler in the kernel code. Is the execution of the system call handler (as part of the kernel code) part of the process, or is it part of the execution of the OS kernel?

The process. The same thing happens with interrupts.

Bill does an I/O request. Jim's process starts to run. Bill's I/O request completes and triggers and interrupt. Jim's process enter's kernel mode and handles Bill's I/O request.

Of course, system security prevents Jim's user mode code from having any access to Bill's data.