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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

Redefining target-dependent system I/O functions in the C library

1.20 Redefining target-dependent system I/O functions in the C library

The default target-dependent I/O functions use semihosting. If any of these functions are redefined, then they must all be redefined.

The function prototypes are contained in rt_sys.h. These functions are called by the C standard I/O library functions. For example, _sys_open() is called by fopen() and freopen(). _sys_open() uses the strings __stdin_name, __stdout_name, and __stderr_name during C library initialization to identify which standard I/O device handle to return. You can leave their values as the default (:tt) if _sys_open() does not use them.

Note

stdin, stdout, and stderr, are interactive devices, but are line-buffered at program startup.
The following example shows you how to redefine the required functions for a device that supports writing but not reading.

Example of retargeting the system I/O functions

/* 
 * These names are used during library initialization as the
 * file names opened for stdin, stdout, and stderr.
 * As we define _sys_open() to always return the same file handle,
 * these can be left as their default values.
 */
const char __stdin_name[] =  ":tt";
const char __stdout_name[] =  ":tt";
const char __stderr_name[] =  ":tt";

FILEHANDLE _sys_open(const char *name, int openmode)
{
  return 1; /* everything goes to the same output */
}
int _sys_close(FILEHANDLE fh)
{
  return 0;
}
int _sys_write(FILEHANDLE fh, const unsigned char *buf,
               unsigned len, int mode)
{
  your_device_write(buf, len);
  return 0;
}
int _sys_read(FILEHANDLE fh, unsigned char *buf,
              unsigned len, int mode)
{
  return -1; /* not supported */
}
void _ttywrch(int ch)
{
  char c = ch;
  your_device_write(&c, 1);
}
int _sys_istty(FILEHANDLE fh)
{
  return 0; /* buffered output */
}
int _sys_seek(FILEHANDLE fh, long pos)
{
  return -1; /* not supported */
}
long _sys_flen(FILEHANDLE fh)
{
  return -1; /* not supported */
}
rt_sys.h defines the type FILEHANDLE. The value of FILEHANDLE is returned by _sys_open() and identifies an open file on the host system.
If the system I/O functions are redefined, both normal character I/O and wide character I/O work. That is, you are not required to do anything extra with these functions for wide character I/O to work.
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