| .. _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. |
| * **"errno" options** |
| - ``LIBC_CONF_ERRNO_MODE``: The implementation used for errno, acceptable values are LIBC_ERRNO_MODE_DEFAULT, LIBC_ERRNO_MODE_UNDEFINED, LIBC_ERRNO_MODE_THREAD_LOCAL, LIBC_ERRNO_MODE_SHARED, LIBC_ERRNO_MODE_EXTERNAL, and LIBC_ERRNO_MODE_SYSTEM. |
| * **"general" options** |
| - ``LIBC_ADD_NULL_CHECKS``: Add nullptr checks in the library's implementations to some functions for which passing nullptr is undefined behavior. |
| * **"math" options** |
| - ``LIBC_CONF_FREXP_INF_NAN_EXPONENT``: The value written back to the second parameter when calling frexp/frexpf/frexpl` with `+/-Inf`/`NaN` is unspecified. Configue an explicit exp value for Inf/NaN inputs. |
| - ``LIBC_CONF_MATH_OPTIMIZATIONS``: Configures optimizations for math functions. Values accepted are LIBC_MATH_SKIP_ACCURATE_PASS, LIBC_MATH_SMALL_TABLES, LIBC_MATH_NO_ERRNO, LIBC_MATH_NO_EXCEPT, and LIBC_MATH_FAST. |
| * **"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_STRERROR``: Disable handling of %m to print strerror in printf and friends. |
| - ``LIBC_CONF_PRINTF_DISABLE_WRITE_INT``: Disable handling of %n in printf format string. |
| - ``LIBC_CONF_PRINTF_FLOAT_TO_STR_NO_SPECIALIZE_LD``: Use the same mode for double and long double in printf. |
| - ``LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_DYADIC_FLOAT``: Use dyadic float for faster and smaller but less accurate printf doubles. |
| - ``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. |
| * **"qsort" options** |
| - ``LIBC_CONF_QSORT_IMPL``: Configures sorting algorithm for qsort and qsort_r. Values accepted are LIBC_QSORT_QUICK_SORT, LIBC_QSORT_HEAP_SORT. |
| * **"scanf" options** |
| - ``LIBC_CONF_SCANF_DISABLE_FLOAT``: Disable parsing floating point values in scanf and friends. |
| - ``LIBC_CONF_SCANF_DISABLE_INDEX_MODE``: Disable index mode in the scanf format string. |
| * **"setjmp" options** |
| - ``LIBC_CONF_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER``: Make setjmp save the value of x18, and longjmp restore it. The AArch64 ABI delegates this register to platform ABIs, which can choose whether to make it caller-saved. |
| * **"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. |
| * **"time" options** |
| - ``LIBC_CONF_TIME_64BIT``: Force the size of time_t to 64 bits, even on platforms where compatibility considerations would otherwise make it 32-bit. |