2.5. Tailoring the C library to a new execution environment
This section describes how to re‑implement functions to produce an application for a different execution environment, for example, embedded in ROM or used with a Real Time Operating System (RTOS).
Symbols that start with a single or double underscore, _ or __, name functions that are used as part of the low‑level implementation. You can re‑implement some of these functions.
Additional information on these library functions is available in the rt_heap.h, rt_locale.h, rt_misc.h, and rt_sys.h include files and the rt_memory.s assembler file.
For descriptions of functions that have the prefix __cxa or __aeabi, see the ARM website for the following specifications:
C Library ABI for the ARM Architecture
Exception Handling ABI for the ARM Architecture
C++ ABI for the ARM Architecture.