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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

Library heap usage requirements of the ARM C and C++ libraries

1.11.1 Library heap usage requirements of the ARM C and C++ libraries

Functions such as malloc() and other dynamic memory allocation functions explicitly allocate memory when used. However, some library functions and mechanisms implicitly allocate memory from the heap.

If heap usage requirements are significant to your code development (for example, you might be developing code for an embedded system with a tiny memory footprint), you must be aware of both implicit and explicit heap requirements.
In C standardlib, implicit heap usage occurs as a result of:
  • Calling the library function fopen() and the first time that an I/O operation is applied to the resulting stream.
  • Passing command-line arguments into the main() function.
The size of heap memory allocated for fopen() is 80 bytes for the FILE structure. When the first I/O operation occurs, and not until the operation occurs, an additional default of 512 bytes of heap memory is allocated for a buffer associated with the operation. You can reconfigure the size of this buffer using setvbuf().
When fclose() is called, the default 80 bytes of memory is kept on a freelist for possible re-use. The 512-byte buffer is freed on fclose().
Declaring main() to take arguments requires 256 bytes of implicitly allocated memory from the heap. This memory is never freed because it is required for the duration of main(). In microlib, main() must not be declared to take arguments, so this heap usage requirement only applies to standardlib. In the standardlib context, it only applies if you have a heap.

Note

The memory sizes quoted might change in future releases.
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