can not find real function address on ARM64 v8

my function name is overwriteFunc, and trying to print function address &overwriteFunc.

I am trying to get function address on ARM64 v8,which returns me a address like this:

Dump of assembler code for function _ZN4test13overwriteFuncEiml@plt:

0x0000000000423a90 <+0>:    adrp    x16, 0x513000
0x0000000000423a94 <+4>:    ldr     x17, [x16,#1640]
0x0000000000423a98 <+8>:    add     x16, x16, #0x668
0x0000000000423a9c <+12>:    br     x17


0x423A90 is not the real function address. it jumps to real function overwriteFunc at the last instruction(x17 contains the real function address). 
Does anyone know why this happens? why ARM has to branch twice instead of once?