5.7.3.6 No-builtin Option

The -fbuiltin option has the compiler produce specialized code that avoids a function call for many built-in functions. The resulting code is often smaller and faster, but since calls to these functions no longer appear in the output, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library. This is the default behavior if no option is specified.

The -fno-builtin option will prevent the compiler from producing special code for built-in functions that are not prefixed with __builtin_.

The -fno-builtin-function form of this option allows you to prevent a built-in version of the named function from being used. In this case, function must not begin with __builtin_. There is no -fbuiltin-function form of this option.