What is the role of stack in a microprocessor?

What is the role of stack in a microprocessor?

Stack is used largely during a function call but depending on the language and level of programming it may be used to temporarily store processor register data or other variables.

Further, the stack may also be used for short-term large-scale storage of data when using recursive functions that store partial data in the stack and call themselves again.

The generic use of stack is for,

1. Return address
   • return value
   • parameters to called function
   • local variables in the called function
   • processor registers that will be reused in the called function

And, yes, stack is also used for exploits.
Its nature of carrying the return-address to where a called function returns back, coupled with the weakness of array-bounds checks in the C language, gives a very nice way to cause buffer overflows in the stack of a vulnerable (unsafely written) program.

At the lowest level the stack is the place where certain instructions store or retrieve data and where data is stored when an interrupt occurs. Microprocesors vary, but there are 5 general types of stack-specific instructions:

1. PUSH - put data onto the stack
2. POP (or PULL) - "remove" data from the stack
3. CALL - jump to a subroutine and put the return address on the stack
4. RETURN - return from a subroutine by loading the program counter with the stack top
5. INT (or SWI) - software interrupt; a specialized CALL

When a processor interrupt occurs (due to an external device), the CPU will save the current program counter and (usually) the flags register on the stack and jump to the handling subroutine. This allows the handling subroutine to process the interrupt and return to whatever the CPU was doing with its current state preserved.

While a microprocessor has only one stack active at a time, the operating system can make it appear as if there are multiple stacks. At least one for the OS, one for each process and one for each thread. In fact, the threads themselves may implement multiple stacks.

At a higher level, whatever language is used to implement a thread will often use the stack for its own purposes to store functional call parameters, local variables and function call return values (speaking in broad strokes here -- consult your languages' low-level documentation for specific detail).

Thus concludes my bottom-up explanation of the stack.

In the early days of computing, subroutine calls were handled by having a word of memory RAM with each subroutine to indicate where it was called from. To call a subroutine, one would do something like:

  load foo_return with #LABEL_123
  goto foo
#LABEL_123:
  ...code to execute after return from foo


foo:
  ... do stuff
  goto foo_return

This pattern might be optimized by having the caller place the return address into a register, and having the routine store it to the "return" spot on entry. This pattern worked, but it had a few problems. Not only did it generally waste memory--it also had no means of dealing with recursive or re-entrant code. Adding a stack made it possible to simplify the code by having the caller simply say "store the return address someplace suitable", without disturbing any earlier ones, and for the called function to simply say "return to the most recent caller that hasn't been returned to yet". This allowed for the development of re-entrant code, and meant that it was only necessary to store enough return addresses to handle the deepest nested chain of function calls that would ever actually occur.

It depends on the microprocessor. Generally its role is keeping local variables and functions' parameters.

And actually it's not in the microprocessor, it's in the central memory.

Stack is used to store and retrieve return addresses during function calls. Its put to good use during nested function calls or recursive function calls. It is also used to transfer arguments to a function.

On a microprocessor it is also used to store the status register contents before a context switch.

cheers