Question

What kind of data is stored in the Kernel mode stack of a process ? Is a processes “user mode” call chain stored in the kernel stack ?

Thanks,
vIjay

Answer 1

Your kernel call chain, and “no”

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The linux kernel is itself a threaded program which works by switching stacks.

So, let’s say you do read(0, space, 100);, or perhaps just c = getchar();, which will eventually turn into a read().

When linux gets control it will start making function calls, naturally using the kernel stack. It will make calls lower and lower in the kernel until it finally gets to a tty or network layer.

But you haven’t typed anything yet!

So it simply switches to another process, one that really is runnable, and it leaves all those function call activation frames on the stack. Eventually you type something and the kernel figures out that your process is now runnable, and when it switches back, again switching stacks, all of those function calls implementing your read(2) can now unwind and eventually return to user mode.