Datasheet

The C and C++ Libraries
ARM DUI 0067D Copyright © 1999-2001 ARM Limited. All rights reserved. 4-67
4.9 Tailoring the runtime memory model
This section describes:
• the management of writable memory by the C library as static data, heap, and
stack
• functions that can be redefined to change how writable memory is managed.
4.9.1 The memory models
You can select either of the following memory models:
Single memory region
The stack grows downward from the top of the memory region while the
heap grows upwards from the bottom of the region. This is the default.
Two memory regions
One memory region is for the stack and the other is for the heap. The size
of the heap region can be zero. The stack region can be in allocated
memory or inherited from the execution environment.
To use the two-region model rather than the default single-region model,
use either:
•
IMPORT __use_two_region_memory from assembly language
•
#pragma import(__use_two_region_memory) from C.
Caution
If you use the two-region memory model and do not provide any heap memory, you
cannot call
malloc() , use stdio , or get command-line arguments for main() .
If you set the size of the heap region to zero and define
__user_heap_extend() as a
function that can extend the heap, the heap is created when it is required.
See the description of
__use_no_heap() in Tailoring storage management on page 4-57,
for how to issue a warning message if the heap or heap region is used.