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Libraries and Floating Point Support Guide

Preface The ARM C and C++ Libraries Mandatory linkage with the C library C and C++ runtime libraries Summary of the C and C++ runtime libraries Compliance with the Application Binary Interface ( Increasing portability of object files to other CL ARM C and C++ library directory structure Selection of ARM C and C++ library variants based Thumb C libraries C and C++ library features C++ and C libraries and the std namespace Multithreaded support in ARM C libraries ARM C libraries and multithreading ARM C libraries and reentrant functions ARM C libraries and thread-safe functions Use of static data in the C libraries Use of the __user_libspace static data area by the C library functions to access subsections of the _ Re-implementation of legacy function __user_libspa Management of locks in multithreaded applications How to ensure re-implemented mutex functions are c Using the ARM C library in a multithreaded environ Thread safety in the ARM C library Thread safety in the ARM C++ library The floating-point status word in a multithreaded Support for building an application with the C lib Using the C library with an application Using the C and C++ libraries with an application Using $Sub$$ to mix semihosted and nonsemihosted I Using the libraries in a nonsemihosting environmen C++ exceptions in a non-semihosting environment Direct semihosting C library function dependencies Indirect semihosting C library function dependenci C library API definitions for targeting a differen Support for building an application without the C Building an application without the C library Creating an application as bare machine C without Integer and floating-point compiler functions and Bare machine integer C Bare machine C with floating-point processing Customized C library startup code and access to C Using low-level functions when exploiting the C li Using high-level functions when exploiting the C l Using malloc() when exploiting the C library Tailoring the C library to a new execution environ Initialization of the execution environment and ex C++ initialization, construction and destruction Exceptions system initialization Emergency buffer memory for exceptions Library functions called from main() Program exit and the assert macro Assembler macros that tailor locale functions in t Link time selection of the locale subsystem in the Runtime selection of the locale subsystem in the C Definition of locale data blocks in the C library LC_CTYPE data block LC_COLLATE data block LC_MONETARY data block LC_NUMERIC data block LC_TIME data block Modification of C library functions for error sign Stack and heap memory allocation and the ARM C and Library heap usage requirements of the ARM C and C Choosing a heap implementation for memory allocati Stack pointer initialization and heap bounds Legacy support for __user_initial_stackheap() Avoiding the heap and heap-using library functions Tailoring input/output functions in the C and C++ Target dependencies on low-level functions in the The C library printf family of functions The C library scanf family of functions Redefining low-level library functions to enable d The C library functions fread(), fgets() and gets( Re-implementing __backspace() in the C library Re-implementing __backspacewc() in the C library Redefining target-dependent system I/O functions i Tailoring non-input/output C library functions Real-time integer division in the ARM libraries ISO C library implementation definition How the ARM C library fulfills ISO C specification mathlib error handling ISO-compliant implementation of signals supported ISO-compliant C library input/output characteristi Standard C++ library implementation definition C library functions and extensions Compiler generated and library-resident helper fun C and C++ library naming conventions Using macro__ARM_WCHAR_NO_IO to disable FILE decla Using library functions with execute-only memory The ARM C Micro-library Floating-point Support The C and C++ Library Functions reference Floating-point Support Functions Reference

Avoiding the heap and heap-using library functions supplied by ARM

1.11.5 Avoiding the heap and heap-using library functions supplied by ARM

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:
  • Re-implement the functions in your own application.
  • Write the application so that it does not call any heap-using function.
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:
  • IMPORT __use_no_heap from assembly language.
  • #pragma import(__use_no_heap) from C.
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>
#pragma import(__use_no_heap)

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.
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