Hijack a weak syscall

Hi, I'm trying to implement kexec as a module. When I do "cat /proc/kallsyms | grep kexec" it gives a out output like this c01b3478 W compat_sys_kexec_load c01b3478 W sys_kexec_load my sys_call_table page is not write protected. So I did *syscall_table[__NR_kexec_load] = (void *)my_kexec; but when I run kexec, It still says "kexec_load function not implimented" When if dig more, The W above means it's a weak symbol. Can I hijack those or, will I have to find another way? Thank you -madushan