As I understand every process have a user stack and kernel stack. Apart from that there is a stack for every mode in ARM achitecture. So I want to know How different stack and stack pointer works in ARM modes? Also when this kernel stack associated with the process will be used ?
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... when this kernel stack associated with the process will be used ?
When you make a system call. Like you want to get IP address of an interface, kernel just like any other application needs some stack to prepare what you want. So it has a corresponding stack when you switch to kernel side of a system call.
How different stack and stack pointer works in ARM modes?
ARM defines a few hardware modes to handle different inputs to the system. For example out of nowhere you can execute an illegal instruction (or undefined). In this case execution in CPU goes into a different mode and needs to be told how to proceed. Since most of the time you require some stack space to be able to handle this gracefully you need a separate stack for this mode. ARM provides you different stack register so when you switch to a different HW mode you don't overwrite previous modes stack pointer.
auselen
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The kernel stack is not associated with any particular process it is used by kernel to keep track of its own functions and the system calls which are invoked by processes.since system call handles kernel data structures its stack can not be maintained on process stack since then process can access private data strucutres of kernel which is harmful to kernel.
nikhil mehta
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..you better read answer http://stackoverflow.com/questions/12911841/kernel-stack-and-user-space-stack/12912556?noredirect=1#comment34343568_12912556 – Rahul Mar 24 '14 at 05:25