help on common symbols

[Vineet Sharma, Noida]

Hi All,
         Suppose we have an example as given below, So what logic decides
the address of common symbol "_x"  and what would be the address filled at
line5?What special handling is needed for coomon symbols? 



.global _y				//line 1
        .data			//line2
        .align  1			//line3
_y:					//line4
        .short  _x+28		//line5
        .global _z		//line6
        .align  1			//line7
_z:					//line8
        .short  1			//line 9
        .comm _x,120		//line 10
        .end			//line 11



Regards
Vineet