Assembly - How to modify stack size?

Question

I am a newbie in assembly programming and I am using push and pop instructions that use the memory stack. So, What is the stack default size, How to modify it and What is th

Answer 1

Whatever loaded ("the loader") your program into memory, and passed control to it, determines where in memory the stack is located, and how much space is available for the stack.

It does so by the simple artifice of loading the stack pointer, typically using a MOV ESP, ... instruction before calling/jumping to your code. Your program then uses the stack area supplied.

If your program uses too much, it will write beyond the end of the allocated stack area. This is a program bug, because the memory past the end may be allocated for some other purpose in the application. Writing on that other memory is likely to change the program behavior (e.g., "bug") when that memory gets used, and finding the cause of that bug is likely to be difficult (people assume that stacks don't damage program data and vice versa).

If your application wants to use a larger stack, generally all you have to do is allocate your own area, large enough for your purposes, and do a MOV ESP, ... yourself to set the stack to the chosen location. How you allocate an area depends on the execution environment in which you run. (You need to respect ESP conventions: must be a multiple of 4, should be initialized to the bottom of a cache line, often useful to initialize to the bottom of virtual memory page).

It is generally a good idea when "switching" stacks to save the old value of ESP provided by the loader, and restore ESP to that old value before returning control to the loader/caller/OS. Likewise, you should free the extended stack space no longer being used.

This scheme will work if you know the amount of stack space you need in advance. In practice, this is rather hard to "guess" (and may be impossible if your code has a recursive algorithm that nests deeply). So you can either pick a really huge number bigger than you need (ick) or you can use an organized approach to switch stacks when it is clear to the program that it needs more. See How does a stackless language work? for more discussion.