Interception of a 64-bit Linux kernel function: 32/64-bit function pointer length?

I am trying to reprogram the old-as-behemoth kernel interception (described in this Phrack question ).

The code to replace the call to a 32-bit function is as follows:

#define SYSMAPADDR 0x12345678
#define CODESIZE 7
static char acct_code[7] = "\xb8\x00\x00\x00\x00"/*movl $0, %eax*/
"\xff\xe0";/*jmp *%eax*/
*(long*)&acct_code[1] = (long)my_hijacking_function;
// here, use either set_pages_rw or trick CR0 to do this:
memcpy(SYSMAPADDR, acct_code, CODESIZE);

But the 64-bit address of the original function is 0xffffffff12345678 (the kernel is located in small memory).

So will the (long) new function pointer match only 4 \ x00 bytes of the movl command?

Btw, please link to Can I replace the Linux kernel function with a module? and Overriding functionality with modules in the Linux kernel , the hacker method described above is more flexible (it can intercept non-extern functions => there is no need to recompile the kernel).