Patch a call instruction in a binary to call another function

patch_call_destination_x64.py

#!/usr/bin/python

import struct
 
filename = "" #change me

#offset in the binary to the call instruction
CALL_OFFSET = 0x00 #change me

#offset in the binary to the destination function
DESTINATION = 0x00 #change me

def relativeAddr(dest, src):
    offset = dest - src
    if offset > 0:
        except Exception("Illegal call!")
    return offset + 0xffffffff - 4
    
data = open(filename, "rb").read()

patched = data[:CALL_OFFSET] + "\xE8" + struct.pack("<I", relativeAddr(DESTINATION, CALL_OFFSET)) + data[CALL_OFFSET+4+1:]

open("{}_patched".format(filename),"wb").write(patched)