If you are developing embedded systems that have limited RAM or that provide their own heap management (for example, an operating system), you might require a system that does not define a heap area. To avoid using the heap you can either:

You can reference the __use_no_heap or __use_no_heap_region symbols in your code to guarantee that no heap-using functions are linked in from the ARM library. You are only required to import these symbols once in your application, for example, using either:

If you include a heap-using function and also reference __use_no_heap or __use_no_heap_region, the linker reports an error. For example, the following sample code results in the linker error shown:

#include <stdio.h>
#include <stdlib.h>
asm("  .global __use_no_heap\n");

void main()
{ 
    char *p = malloc(256);
    ...
}

Error: L6915E: Library reports error: __use_no_heap was requested, but malloc was referenced

To find out which objects are using the heap, link with --verbose --list=out.txt, search the output for the relevant symbol (in this case malloc), and find out what object referenced it.

__use_no_heap guards against the use of malloc(), realloc(), free(), and any function that uses those functions. For example, calloc() and other stdio functions.

__use_no_heap_region has the same properties as __use_no_heap, but in addition, guards against other things that use the heap memory region. For example, if you declare main() as a function taking arguments, the heap region is used for collecting argc and argv.