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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

Building an application without the C library

1.7.1 Building an application without the C library

If your application does not initialize the C library, a number of functions are not available in your application.

Creating an application that has a main() function causes the C library initialization functions to be included as part of __rt_lib_init.
If your application does not have a main() function, the C library is not initialized and the following functions are not available in your application:
  • Low-level stdio functions that have the prefix _sys_.
  • Signal-handling functions, signal() and raise() in signal.h.
  • Other functions, such as atexit().
The following table shows header files, and the functions they contain, that are available with an uninitialized library. Some otherwise unavailable functions can be used if the library functions they depend on are re-implemented.

Table 1-5 Standalone C library functions

Function Description
alloca.h
Functions in this file work without any library initialization or function re-implementation. You must know how to build an application with the C library to use this header file.
assert.h
Functions listed in this file require high-level stdio, __rt_raise(), and _sys_exit(). You must be familiar with tailoring error signaling, error handling, and program exit to use this header file.
ctype.h
Functions listed in this file require the locale functions.
errno.h
Functions in this file work without the requirement for any library initialization or function re-implementation.
fenv.h
Functions in this file work without the requirement for any library initialization and only require the re-implementation of __rt_raise().
float.h
This file does not contain any code. The definitions in the file do not require library initialization or function re-implementation.
inttypes.h
Functions listed in this file require the locale functions.
limits.h
Functions in this file work without the requirement for any library initialization or function re-implementation.
locale.h
Call setlocale() before calling any function that uses locale functions. For example:
setlocale(LC_ALL, "C");
See the contents of locale.h for more information on the following functions and data structures:
  • setlocale() selects the appropriate locale as specified by the category and locale arguments.
  • lconv is the structure used by locale functions for formatting numeric quantities according to the rules of the current locale.
  • localeconv() creates an lconv structure and returns a pointer to it.
  • _get_lconv() fills the lconv structure pointed to by the parameter. This ISO extension removes the requirement for static data within the library.
locale.h also contains constant declarations used with locale functions.
math.h
For functions in this file to work, you must first call _fp_init() and re-implement __rt_raise().
setjmp.h
Functions in this file work without any library initialization or function re-implementation.
signal.h
Functions listed in this file are not available without library initialization. You must know how to build an application with the C library to use this header file.
__rt_raise() can be re-implemented for error and exit handling. You must be familiar with tailoring error signaling, error handling, and program exit.
stdarg.h
Functions listed in this file work without any library initialization or function re-implementation.
stddef.h
This file does not contain any code. The definitions in the file do not require library initialization or function re-implementation.
stdint.h
This file does not contain any code. The definitions in the file do not require library initialization or function re-implementation.
stdio.h
The following dependencies or limitations apply to these functions:
  • The high-level functions such as printf(), scanf(), puts(), fgets(), fread(), fwrite(), and perror() depend on lower-level stdio functions fgetc(), fputc(), and __backspace(). You must re-implement these lower-level functions when using the standalone C library.
    However, you cannot re-implement the _sys_ prefixed functions (for example, _sys_read()) when using the standalone C library because the layer of stdio that calls the _sys_ functions requires library initialization.
    You must be familiar with tailoring the input/output functions in the C and C++ libraries.
  • The printf() and scanf() family of functions require locale.
  • The remove() and rename() functions are system-specific and probably not usable in your application.
stdlib.h
Most functions in this file work without any library initialization or function re-implementation. The following functions depend on other functions being instantiated correctly:
  • ato*() requires locale.
  • strto*() requires locale.
  • malloc(), calloc(), realloc(), and free() require heap functions.
  • atexit() is not available when building an application without the C library.
string.h
Functions in this file work without any library initialization, with the exception of strcoll() and strxfrm(), that require locale.
time.h
mktime() and localtime() can be used immediately
time() and clock() are system-specific and are probably not usable unless re-implemented
asctime(), ctime(), and strftime() require locale.
wchar.h
Wide character library functions added to ISO C by Normative Addendum 1 in 1994.
The following dependencies or limitations apply to these functions:
  • The high-level functions such as swprintf(), vswprintf(), swscanf(), and vswscanf() depend on lower-level stdio functions such as fgetwc() and fputwc(). You must re-implement these lower-level functions when using the standalone C library. See 1.13 Target dependencies on low-level functions in the C and C++ libraries for more information.
  • The high-level functions such as swprintf(), vswprintf(), swscanf(), and vswscanf() require locale.
  • All the conversion functions (for example, btowc, wctob, mbrtowc, and wcrtomb) require locale.
  • wcscoll() and wcsxfrm() require locale.
wctype.h
Wide character library functions added to ISO C by Normative Addendum 1 in 1994. This requires locale.
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