llvm/libc/config/config.json

{
  "errno": {
    "LIBC_CONF_ERRNO_MODE": {
      "value": "LIBC_ERRNO_MODE_DEFAULT",
      "doc": "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, LIBC_ERRNO_MODE_SYSTEM, and LIBC_ERRNO_MODE_SYSTEM_INLINE."
    }
  },
  "threads": {
    "LIBC_CONF_THREAD_MODE": {
      "value": "LIBC_THREAD_MODE_PLATFORM",
      "doc": "The implementation used for Mutex, acceptable values are LIBC_THREAD_MODE_PLATFORM, LIBC_THREAD_MODE_SINGLE, and LIBC_THREAD_MODE_EXTERNAL."
    }
  },
  "printf": {
    "LIBC_CONF_PRINTF_DISABLE_FLOAT": {
      "value": false,
      "doc": "Disable printing floating point values in printf and friends."
    },
    "LIBC_CONF_PRINTF_DISABLE_INDEX_MODE": {
      "value": false,
      "doc": "Disable index mode in the printf format string."
    },
    "LIBC_CONF_PRINTF_DISABLE_WRITE_INT": {
      "value": false,
      "doc": "Disable handling of %n in printf format string."
    },
    "LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE": {
      "value": false,
      "doc": "Use large table for better printf long double performance."
    },
    "LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_DYADIC_FLOAT": {
      "value": false,
      "doc": "Use dyadic float for faster and smaller but less accurate printf doubles."
    },
    "LIBC_CONF_PRINTF_FLOAT_TO_STR_NO_SPECIALIZE_LD": {
      "value": false,
      "doc": "Use the same mode for double and long double in printf."
    },
    "LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_FLOAT320": {
      "value": false,
      "doc": "Use an alternative printf float implementation based on 320-bit floats"
    },
    "LIBC_CONF_PRINTF_DISABLE_FIXED_POINT": {
      "value": false,
      "doc": "Disable printing fixed point values in printf and friends."
    },
    "LIBC_CONF_PRINTF_DISABLE_STRERROR": {
      "value": false,
      "doc": "Disable handling of %m to print strerror in printf and friends."
    },
    "LIBC_CONF_PRINTF_RUNTIME_DISPATCH": {
      "value": true,
      "doc": "Use dynamic dispatch for the output mechanism to reduce code size."
    }
  },
  "scanf": {
    "LIBC_CONF_SCANF_DISABLE_FLOAT": {
      "value": false,
      "doc": "Disable parsing floating point values in scanf and friends."
    },
    "LIBC_CONF_SCANF_DISABLE_INDEX_MODE": {
      "value": false,
      "doc": "Disable index mode in the scanf format string."
    }
  },
  "string": {
    "LIBC_CONF_STRING_UNSAFE_WIDE_READ": {
      "value": false,
      "doc": "Read more than a byte at a time to perform byte-string operations like strlen."
    },
    "LIBC_CONF_MEMSET_X86_USE_SOFTWARE_PREFETCHING": {
      "value": false,
      "doc": "Inserts prefetch for write instructions (PREFETCHW) for memset on x86 to recover performance when hardware prefetcher is disabled."
    }
  },
  "codegen": {
    "LIBC_CONF_KEEP_FRAME_POINTER": {
      "value": true,
      "doc": "Keep frame pointer in functions for better debugging experience."
    },
    "LIBC_CONF_ENABLE_STRONG_STACK_PROTECTOR": {
      "value": true,
      "doc": "Enable -fstack-protector-strong to defend against stack smashing attack."
    }
  },
  "pthread": {
    "LIBC_CONF_TIMEOUT_ENSURE_MONOTONICITY": {
      "value": true,
      "doc": "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."
    },
    "LIBC_CONF_RAW_MUTEX_DEFAULT_SPIN_COUNT": {
      "value": 100,
      "doc": "Default number of spins before blocking if a mutex is in contention (default to 100)."
    },
    "LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT": {
      "value": 100,
      "doc": "Default number of spins before blocking if a rwlock is in contention (default to 100)."
    }
  },
  "math": {
    "LIBC_CONF_MATH_OPTIMIZATIONS": {
      "value": 0,
      "doc": "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."
    },
    "LIBC_CONF_FREXP_INF_NAN_EXPONENT": {
      "value": "",
      "doc": "The value written back to the second parameter when calling frexp/frexpf/frexpl` with `+/-Inf`/`NaN` is unspecified.  Configure an explicit exp value for Inf/NaN inputs."
    }
  },
  "qsort": {
    "LIBC_CONF_QSORT_IMPL": {
      "value": "LIBC_QSORT_QUICK_SORT",
      "doc": "Configures sorting algorithm for qsort and qsort_r. Values accepted are LIBC_QSORT_QUICK_SORT, LIBC_QSORT_HEAP_SORT."
    }
  },
  "setjmp": {
    "LIBC_CONF_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER": {
      "value": true,
      "doc": "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."
    }
  },
  "time": {
    "LIBC_CONF_TIME_64BIT": {
      "value": false,
      "doc": "Force the size of time_t to 64 bits, even on platforms where compatibility considerations would otherwise make it 32-bit."
    }
  },
  "general": {
    "LIBC_ADD_NULL_CHECKS": {
      "value": true,
      "doc": "Add nullptr checks in the library's implementations to some functions for which passing nullptr is undefined behavior."
    }
  }
}