Function memmem 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn memmem(
    haystack: *const c_void,
    haystacklen: size_t,
    needle: *const c_void,
    needlelen: size_t,
) -> *mut c_void

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/memmem.html.

Safety

The caller must ensure that:

• haystack is convertible to a &[u8] with length haystacklen, and
• needle is convertible to a &[u8] with length needlelen.