libc/docs/configure.rst

.. _configure:
..
   Do not edit this file directly. CMake will auto generate it.
   If the changes are intended, add this file to your commit.

==========================
Configure Options
==========================

Below is the full set of options one can use to configure the libc build.
An option can be given an explicit value on the CMake command line using
the following syntax:

.. code-block:: sh

  $> cmake <other build options> -D<libc config option name>=<option value> <more options>

For example:

.. code-block:: sh

  $> cmake <other build options> -DLIBC_CONF_PRINTF_DISABLE_FLOAT=ON <more options>

See the main ``config/config.json``, and the platform and architecture specific
overrides in ``config/<platform>/config.json`` and ``config/<platform>/<arch>/config.json,``
to learn about the defaults for your platform and target.

* **"codegen" options**
    - ``LIBC_CONF_ENABLE_STRONG_STACK_PROTECTOR``: Enable -fstack-protector-strong to defend against stack smashing attack.
    - ``LIBC_CONF_KEEP_FRAME_POINTER``: Keep frame pointer in functions for better debugging experience.
* **"malloc" options**
    - ``LIBC_CONF_FREELIST_MALLOC_BUFFER_SIZE``: Default size for the constinit freelist buffer used for the freelist malloc implementation (default 1o 1GB).
* **"printf" options**
    - ``LIBC_CONF_PRINTF_DISABLE_FIXED_POINT``: Disable printing fixed point values in printf and friends.
    - ``LIBC_CONF_PRINTF_DISABLE_FLOAT``: Disable printing floating point values in printf and friends.
    - ``LIBC_CONF_PRINTF_DISABLE_INDEX_MODE``: Disable index mode in the printf format string.
    - ``LIBC_CONF_PRINTF_DISABLE_WRITE_INT``: Disable handling of %n in printf format string.
    - ``LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE``: Use large table for better printf long double performance.
* **"pthread" options**
    - ``LIBC_CONF_RAW_MUTEX_DEFAULT_SPIN_COUNT``: Default number of spins before blocking if a mutex is in contention (default to 100).
    - ``LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT``: Default number of spins before blocking if a rwlock is in contention (default to 100).
    - ``LIBC_CONF_TIMEOUT_ENSURE_MONOTONICITY``: Automatically adjust timeout to CLOCK_MONOTONIC (default to true). POSIX API may require CLOCK_REALTIME, which can be unstable and leading to unexpected behavior. This option will convert the real-time timestamp to monotonic timestamp relative to the time of call.
* **"string" options**
    - ``LIBC_CONF_MEMSET_X86_USE_SOFTWARE_PREFETCHING``: Inserts prefetch for write instructions (PREFETCHW) for memset on x86 to recover performance when hardware prefetcher is disabled.
    - ``LIBC_CONF_STRING_UNSAFE_WIDE_READ``: Read more than a byte at a time to perform byte-string operations like strlen.