 RealView Libraries and Floating Point Support Guide | |
| Home Products Events Support | |
Technical Support
On-Line Manuals
RealView Libraries and Floating Point Support Guide
Preface Introduction The C and C++ Libraries About the C and C++ libraries
Features of the C and C++ libraries Namespaces Writing reentrant and thread‑safe code Introduction to reentrancy and thread‑safety Use of static data in the C libraries The __user_libspace static data area Managing locks in multithreaded applications Using the ARM C libraries with a multithreaded app Thread‑safety in the ARM C libraries Thread‑safety in the ARM C++ libraries Building an application with the C library Using the libraries with an application Building an application for a semihosted environme Building an application for a non semihosting envi Building an application without the C library Integer and FP helper functions Bare machine integer C Bare machine C with floating‑point Exploiting the C library The standalone C library functions Tailoring the C library to a new execution environ How C and C++ programs use the library functions __rt_entry Exiting from the program __rt_exit() __rt_lib_init() __rt_lib_shutdown() Tailoring static data access Tailoring locale and CTYPE using assembler macros Selecting locale at link time Selecting locale at runtime Defining a locale block LC_CTYPE data block LC_COLLATE data block LC_MONETARY data block LC_NUMERIC data block LC_TIME data block _get_lconv() localeconv() setlocale() _findlocale() The lconv structure Tailoring locale and CTYPE using C macros Selecting locale at link time Selecting locale at runtime Macros and utility functions _get_lc_ctype() _get_lc_collate() _get_lc_monetary() _get_lc_numeric() _get_lc_time() _get_lconv() localeconv() setlocale() _findlocale() __LC_CTYPE_DEF __LC_COLLATE_DEF __LC_TIME_DEF __LC_NUMERIC_DEF __LC_MONETARY_DEF __LC_INDEX_END The lconv structure Tailoring error signaling, error handling, and pro _sys_exit() errno __rt_errno_addr() __raise() __rt_raise() __default_signal_handler() _ttywrch() __rt_fp_status_addr() Tailoring storage management Avoiding the ARM‑supplied heap and heap‑using Support for malloc Tailoring the runtime memory model The memory models Controlling the runtime memory model Writing your own memory model __user_initial_stackheap() __user_setup_stackheap() __user_heap_extend() __user_heap_extent() __user_stack_cleanup_space() __rt_heap_extend() __rt_stack_postlongjmp() Tailoring the input/output functions Dependencies on low‑level functions Target‑dependent input/output support functions _sys_open() _sys_close() _sys_read() _sys_write() _sys_ensure() _sys_flen() _sys_seek() _sys_istty() _sys_tmpnam() _sys_command_string() #pragma import(_main_redirection) Tailoring other C library functions clock() _clock_init() time() remove() rename() system() getenv() _getenv_init() Selecting real‑time division ISO implementation definition ISO C library implementation definition Standard C++ library implementation definition C library extensions atoll() strtoll() strtoull() printf() snprintf() vsnprintf() lldiv() llabs() wcstombs() alloca() strlcpy() strlcat() _fisatty() __heapstats() __heapvalid() Library naming conventions Placing ARM libraries Helper libraries Identifying library variants The C Micro-library Floating‑point SupportThe __user_libspace static data area
  | |||
  |  | ||
| |||
| Home > The C and C++ Libraries > Writing reentrant and thread‑safe code > The __user_libspace static data area | |||
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 settingerrno. By default,__rt_errno_addr()returns a pointer toerrno.The 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 themalloc‑related functions.The
allocastate, used byalloca()and its helper functions.The current locale settings, used by functions such as
setlocale(), but also used by all other library functions which depend on them. For example, thectype.hfunctions have to access theLC_CTYPEsetting.
The C++ libraries use the __user_libspace area to hold:
The
new_handlerfield andddtor_pointer:the
new_handlerfield is used to keep track of the value passed tostd::set_new_handler()the
ddtor_pointeris used by__cxa_atexit()and__aeabi_atexit().
C++ exception handling information for functions such as
std::set_terminate()andstd::set_unexpected().
For more information on __aeabi_atexit(), std::set_terminate() and std::set_unexpected(), see the ARM website for the following specifications: CPPABI and the Exception Handling ABI for the ARM Architecture.
Note
How the C and C++ libraries use the __user_libspace area might change in future releases.
Two wrapper functions are provided to return a subsection of the __user_libspace static data area:
__user_perproc_libspace()Returns a pointer to 96 bytes used to store data that is global to an entire process, that is data shared between all threads.
__user_perthread_libspace()Returns a pointer to 96 bytes used to store data that is local to a particular thread. This means that
__user_perthread_libspace()returns a different address depending on the thread it is called from.
The __user_libspace() function does not normally have to be redefined. However, if you are writing an operating system or a process switcher, you must re‑implement this function. See Tailoring static data access for more information.
Where you are porting single‑threaded processes to RVCT that re‑implement this function, you can continue to do this without having to change your code. The change in behavior is, however, important if you are using RVCT to write multithreaded applications.
| Copyright © 2007 ARM Limited. All rights reserved. | ARM DUI 0378A |
 PDF version | |
| Home > The C and C++ Libraries > Writing reentrant and thread‑safe code > The __user_libspace static data area | |
| |
| Contact Site Map Press Privacy | Copyright © 2008 Keil™, An ARM® Company. All rights reserved. |
