5. Data Race

$ objdump -d t1 > t1.disasm.txt   #   (note on %rip addressing)

...
 a4a:	8b 05 dc 15 20 00    	mov    0x2015dc(%rip),%eax        # 20202c <counter>
 a50:	83 c0 01             	add    $0x1,%eax
 a53:	89 05 d3 15 20 00    	mov    %eax,0x2015d3(%rip)        # 20202c <counter>
...

Textbook example:

 mov 0x8049a1c, %eax
 add $0x1, %eax
 mov %eax, 0x8049a1c

Need mutual exclusion or atomic operations