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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

Customized C library startup code and access to C library functions

1.7.6 Customized C library startup code and access to C library functions

If you build an application with customized startup code, you must either avoid functions that require initialization or provide the initialization and low-level support functions.

When building an application without the C library, if you create an application that includes a main() function, the linker automatically includes the initialization code necessary for the execution environment. There are situations where this is not desirable or possible. For example, a system running a Real-Time Operating System (RTOS) might have its execution environment configured by the RTOS startup code.
You can create an application that consists of customized startup code and still use many of the library functions. You must either:
  • Avoid functions that require initialization.
  • Provide the initialization and low-level support functions.
The functions you must re-implement depend on how much of the library functionality you require:
  • If you want only the compiler support functions for division, structure copy, and floating-point arithmetic, you must provide __rt_raise(). This also enables very simple library functions such as those in errno.h, setjmp.h, and most of string.h to work.
  • If you call setlocale() explicitly, locale-dependent functions are activated. This enables you to use the atoi family, sprintf(), sscanf(), and the functions in ctype.h.
  • Programs that use floating-point must call _fp_init(). If you select software floating-point in --fpmode=ieee_fixed or --fpmode=ieee_full mode, the program must also provide __rt_fp_status_addr().
  • Implementing high-level input/output support is necessary for functions that use fprintf() or fputs(). The high-level output functions depend on fputc() and ferror(). The high-level input functions depend on fgetc() and __backspace().
Implementing these functions and the heap enables you to use almost the entire library.
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