nuttx/Documentation/components/libs/index.rst

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===============
NuttX libraries
===============
This page discusses the NuttX libraries that can be found in ``libs/``
Libraries in NuttX are very special creatures. They have these properties:
#. They can be shared by both application logic and logic within the OS when
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using the FLAT build.
#. But in PROTECTED and KERNEL modes, they must be built differently: The
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copies used by applications and the OS cannot be the same. Rather,
separate versions of libraries must be built for the kernel and for
applications.
#. When used by the OS, some special care must be taken to assure that the
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OS logic does not disrupt the user's errno value and that the OS does
not create inappropriate cancellation points.
For example, ``sem_wait()`` is both a cancellation point and modifies the
errno value. So within the FLAT build and without kernel version for
the PROTECTED and KERNEL builds, the special internal OS interface
``nxsem_wait()`` must be used. Within libraries, the macro ``_SEM_WAIT()``
(as defined in ``include/nuttx/semaphore.h``) is used instead. The
definition of this macro accounts for the different usage environments.
NOTE: The libraries under ``libs/`` build differently from other NuttX
components: There are no build-related files in the ``libs/`` directory; it
is simply a container for other well-known, individual library directories.
The upper level Makefile logic is aware of the libraries within the ``libs/``
container.
The only real function of the ``libs/`` directory is to prevent the top-level
directory from becoming cluttered with individual libraries.
.. toctree::
:maxdepth: 1
:caption: Contents:
libc/index.rst
libdsp.rst
libm.rst
libxx.rst
libnx/index.rst