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Similarly to a stack of plates, adding or removing is only practical at the top. Simple representation of a stack runtime with push and pop operations.. In computer science, a stack is an abstract data type that serves as a collection of elements with two main operations:
To save a value to the stack, the PUSH instruction is used. To retrieve a value from the stack, the POP instruction is used. Example: Assuming that SS = 1000h and SP = 0xF820. This means that current stack top is the physical address 0x1F820 (this is due to memory segmentation in 8086). The next two machine instructions of the program are:
The stack is often used to store variables of fixed length local to the currently active functions. Programmers may further choose to explicitly use the stack to store local data of variable length. If a region of memory lies on the thread's stack, that memory is said to have been allocated on the stack, i.e. stack-based memory allocation (SBMA).
In addition, the stack pointer must always be 4-byte aligned, and must always be 8-byte aligned at a function call with a public interface. [3] This calling convention causes a "typical" ARM subroutine to: In the prologue, push r4 to r11 to the stack, and push the return address in r14 to the stack (this can be done with a single STM instruction);
With a stack stored completely in RAM, this does implicit writes and reads of the in-memory stack: Load X, push to memory; Load 1, push to memory; Pop 2 values from memory, add, and push result to memory; for a total of 5 data cache references. The next step up from this is a stack machine or interpreter with a single top-of-stack register.
The choice of segment is normally defaulted by the processor according to the function being executed. Instructions are always fetched from the code segment. Any stack push or pop or any data reference referring to the stack uses the stack segment. All other references to data use the data segment.
This type of stack is also known as an execution stack, program stack, control stack, run-time stack, or machine stack, and is often shortened to simply the "stack". Although maintenance of the call stack is important for the proper functioning of most software , the details are normally hidden and automatic in high-level programming languages .
Commonly provided are dup, to duplicate the element atop the stack, exch (or swap), to exchange elements atop the stack (the first becomes second and the second becomes first), roll, to cyclically permute elements in the stack or on part of the stack, pop (or drop), to discard the element atop the stack (push is implicit), and others. These ...