Keil Logo Arm Logo

Technical Support

On-Line Manuals

Libraries and Floating Point Support Guide

Conventions and feedback The ARM C and C++ libraries Mandatory linkage with the C library C and C++ runtime libraries C and C++ library features Library heap usage requirements of the ARM C and C 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 libraries and the std namespace 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 Using the C library with an application Using the C and C++ libraries with an application Using $Sub$$ to mix semihosted and nonsemihosted I Using the libraries in a nonsemihosting environmen C++ exceptions in a non-semihosting environment Direct semihosting C library function dependencies Indirect semihosting C library function dependenci C library API definitions for targeting a differen Building an application without the C library Creating an application as bare machine C without Integer and floating-point compiler functions and Bare machine integer C Bare machine C with floating-point processing Customized C library startup code and access to C Program design when exploiting the C library Using low-level functions when exploiting the C li Using high-level functions when exploiting the C l Using malloc() when exploiting the C library Tailoring the C library to a new execution environ How C and C++ programs use the library functions Initialization of the execution environment and ex C++ initialization, construction and destruction Legacy support for C$$pi_ctorvec instead of .init_ 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 ISO8859-1 implementation Shift-JIS and UTF-8 implementation 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 Modification of memory management functions in the Avoiding the heap and heap-using library functions C library support for memory allocation functions Heap1, standard heap implementation Heap2, alternative heap implementation Using a heap implementation from bare machine C Stack pointer initialization and heap bounds Defining __initial_sp, __heap_base and __heap_limi Extending heap size at runtime Legacy support for __user_initial_stackheap() 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 Selecting real-time division in the ARM libraries 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 Persistence of C and C++ library names across rele Link time selection of C and C++ libraries Managing projects that have explicit C or C++ libr Compiler generated and library-resident helper fun C and C++ library naming conventions Using macro__ARM_WCHAR_NO_IO to disable FILE decla The ARM C micro-library Floating-point support

Libraries and Floating Point Support Guide

Use of the __user_libspace static data area by the C libraries

Use of the __user_libspace static data area by the C libraries

The __user_libspace static data area holds the static data for the C libraries. This is a block of 96 bytes of zero-initialized data, supplied by the C library. It is also used as a temporary stack during C library initialization.

The default ARM C libraries use the __user_libspace area to hold:

  • errno, used by any function that is capable of setting errno. By default, __rt_errno_addr() returns a pointer to errno.

  • The Floating-Point (FP) status word for software floating-point (exception flags, rounding mode). It is unused in hardware floating-point. By default, __rt_fp_status_addr() returns a pointer to the FP status word.

  • A pointer to the base of the heap (that is, the __Heap_Descriptor), used by all the malloc-related functions.

  • The current locale settings, used by functions such as setlocale(), but also used by all other library functions that depend on them. For example, the ctype.h functions have to access the LC_CTYPE setting.

The C++ libraries use the __user_libspace area to hold:

  • the new_handler field and ddtor_pointer:

    • the new_handler field is used to keep track of the value passed to std::set_new_handler()

    • the ddtor_pointer, that points to a list of destructions to be performed on program exit. For example, objects constructed outside function scope exist for the duration of the program, but require destruction on program exit. The ddtor_pointer is used by __cxa_atexit() and __aeabi_atexit().

  • C++ exception handling information for functions such as std::set_terminate() and std::set_unexpected().

Note

How the C and C++ libraries use the __user_libspace area might change in future releases.

Show/hideSee also

Other information
Copyright © 2007-2008, 2011-2012 ARM. All rights reserved.ARM DUI 0378D
Non-ConfidentialID062912

arm-logo-small

Keil logo
Important information

This site uses cookies to store information on your computer. By continuing to use our site, you consent to our cookies.