Function Perl_unpackstring 

pub unsafe fn Perl_unpackstring(
    my_perl: *mut PerlInterpreter,
    pat: *const c_char,
    patend: *const c_char,
    s: *const c_char,
    strend: *const c_char,
    flags: U32,
) -> isize

thx shim for crate::Perl_unpackstring.