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:

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

For example:

$> 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.

  • “printf” options
    • 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.

  • “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.