Identifying the type of the kernel routine executing in the kernel at a particular time instant

[limp]

Hi all,

I know that kernel routines can be activated in several ways and many
different things can be executed in the kernel:

. A process invokes a system call (a system call is executed in the kernel).
. The CPU executing a process, signals an exception (e.g. due to an invalid
instruction). In this case, an exception handler is executed under the
kernel on behalf of the process that caused it.
. A peripheral device issues an interrupt signal to the CPU and the kernel
executes the corresponding interrupt handler. 
. A kernel thread is executed in the kernel.

What I want to do is to find a way of identifying what is currently executed
under the kernel by either looking the values of CPU registers (I am talking
about the x86 architecture) or by looking at particular flags or values
being set in various Linux structures (such as the task_struct). In
particular, I want to know if a kernel thread, an interrupt handler, an
exception handler, etc is executed at a particular time instant in the
kernel.

For example, is there a way to tell that a system call is executed (and
ideally, which one)? Would the execution of a system call set a particular
value to a CPU register or to the task_struct of the process of which is
executed under?

Regarding the peripheral interrupt case, I guess we can tell if an interrupt
handler is executed by looking at the ISR flags of the used by Linux
interrupt controller(s). What I would like is to find out similar tricks for
identifying any other possible kernel routines that could be executed (e.g.
system call, exception handler, etc.).

Any help will be much appreciated.

Kind regards,

John K.