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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 SupportUse of static data in the C libraries
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| Home > The C and C++ Libraries > Writing reentrant and thread‑safe code > Use of static data in the C libraries | |||
Static data refers to persistent read/write data that is not stored on the stack or the heap. This persistent data can be external or internal in scope, and is:
at a fixed address, when compiled with
‑‑apcs /norwpiat a fixed address relative to the static base
, registerr9, when compiled with‑‑apcs /rwpi.
Libraries that use static data might be reentrant, but this depends on their use of the __user_libspace static data area, and on the build options you choose:
When compiled with
‑‑apcs /norwpi, read/write static data is addressed in a position‑dependent fashion. This is the default. Code from these variants is single‑threaded because it uses read/write static data.When compiled with
‑‑apcs /rwpi, read/write static data is addressed in a position‑independent fashion using offsets from the static base registersb. Code from these variants is reentrant and can be multiply threaded if each thread uses a different static base value.
The following describes how the C libraries use static data:
The default floating‑point arithmetic libraries
fz_*andfj_*do not use static data and are always reentrant. However, thef_*andg_*libraries do use static data.All statically‑initialized data in the C libraries is read‑only.
All writable static data is zero initialized.
Most C library functions use no writable static data and are reentrant whether built with default build options,
‑‑apcs /norwpior reentrant build options,‑‑apcs /rwpi.Some functions have static data implicit in their definitions. You must not use these in a reentrant application unless you build it with
‑‑apcs /rwpiand the caller uses different values insb.
See Position independence qualifiers in the Compiler User Guide for information on the ‑‑apcs build options described here.
Note
Exactly which functions use static data in their definitions might change in future releases.
| Copyright © 2007 ARM Limited. All rights reserved. | ARM DUI 0378A |
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