The C library requires you to specify where the stack pointer begins. If you intend to use ARM library functions that use the heap, for example, malloc(), calloc(), or if you define argc and argv command-line arguments for main(), the C library also requires you to specify which region of memory the heap is intially expected to use.

The region of memory used by the heap can be extended at a later stage of program execution, if required.

You can specify where the stack pointer begins, and which region of memory the heap is intially expected to use, with any of the following methods:

The initial stack pointer must be aligned to a multiple of eight bytes.

By default, if memory allocated for the heap is destined to overlap with memory that lies in close proximity with the stack, the potential collision of heap and stack is automatically detected and the requested heap allocation fails. If you do not require this automatic collision detection, you can save a small amount of code size by disabling it with #pragma import __use_two_region_memory.

Although it is possible to automatically detect expansion of the heap into the stack, it is not possible to automatically detect expansion of the stack into heap memory.

For legacy purposes, it is possible for you to bypass all of these methods and behavior. You can do this by defining the following functions to perform your own stack and heap memory management: