Function drmgr_insert_read_cls_field 

pub unsafe extern "C" fn drmgr_insert_read_cls_field(
    drcontext: *mut c_void,
    idx: c_int,
    ilist: *mut instrlist_t,
    where_: *mut instr_t,
    reg: reg_id_t,
) -> bool_

Inserts into \p ilist prior to \p where meta-instruction(s) to read into the general-purpose full-size register \p reg from the user-controlled drcontext field for the current (at execution time) callback and index. Reads from the same field as drmgr_get_cls_field(). \return whether successful.