Stackutrymme

Stackutrymme, or stack space, is the region of a program’s memory reserved for the execution stack used to manage function calls. It is separate from the heap and is typically used for automatic storage duration objects, such as local variables, and for storing return addresses and saved registers.

The stack operates in a last-in, first-out (LIFO) fashion. Each time a function is called, a new stack frame is created, containing the return address, the caller’s context, parameters that must be preserved, and space for local variables. When the function returns, its frame is removed from the stack and control returns to the caller. The stack pointer registers point to the top of the stack and are managed by the processor and compiler.

In most architectures, the stack grows downward in memory; pushing a frame subtracts from the stack pointer. Some systems may use upward-growing stacks. Each thread typically has its own stack with a fixed or expandable size, determined by the operating system or runtime.

Stack versus heap: stack allocation is automatic and fast, with deallocation occurring when the function returns. Heap allocation is dynamic and typically requires explicit management or garbage collection. Excessive stack usage can lead to stack overflow, causing crashes or security vulnerabilities.

Security and reliability: Stack overflows are a common vector for crashes and exploits. Protections include stack canaries, non-executable stacks (NX), address space layout randomization (ASLR), and bounds checking. Practical considerations include avoiding large local arrays in languages like C and C++, or allocating sizable data on the heap when appropriate, especially in recursive or deeply nested calls.