I recently started looking at the 'end' specification for the USING statement,
something I've neglected for a long time. I *thought* it indicated the last
location that could be assembled with that USING, but I'm not so sure any more.
I have the following source file:
dummy csect ,
using (dummy,dummy+6000),1
ceject 0
lg 1,far1
lg 1,far2
lg 1,far3
lg 1,far4
org dummy+4000
far1 dc ad(1)
org dummy+5000
far2 dc ad(2)
org dummy+6000
far3 dc ad(3)
org dummy+7000
far4 dc ad(4)
end ,
The relevant portion of the listing looks like this:
Loc Object Code Addr1 Addr2 Stmt Source Statement
00000000 00000000 00001B60 1 dummy csect ,
R:1 00000000 2 using
(dummy,dummy+6000),1
Active Usings: dummy(X'1770'),R1
Loc Object Code Addr1 Addr2 Stmt Source Statement
00000000 E310 1FA0 0004 00000FA0 4 lg 1,far1
00000006 E310 1388 0104 00001388 5 lg 1,far2
0000000C E310 1770 0104 00001770 6 lg 1,far3
00000012 E310 1B58 0104 00001B58 7 lg 1,far4
00000018 00000018 00000FA0 9 org dummy+4000
00000FA0 0000000000000001 10 far1 dc ad(1)
00000FA8 00000FA8 00001388 11 org dummy+5000
00001388 0000000000000002 12 far2 dc ad(2)
00001390 00001390 00001770 13 org dummy+6000
00001770 0000000000000003 14 far3 dc ad(3)
00001778 00001778 00001B58 15 org dummy+7000
00001B58 0000000000000004 16 far4 dc ad(4)
17 end ,
The last sentence of the description of the 'end' specification for an ordinary
USING says, "Thus USING base,reg is equivalent to USING (base,base+4096),reg."
So, my thinking was as follows:
- Since a "default" USING can only be used up to base+4095 (because the maximum
4K displacement is x'FFF'), I assume this means that the 'base+4096' points to
the byte *past* the last valid USING location.
- If the previous item is true then the "Active Usings" line that shows a range
of x'1770' bytes for 'dummy' would mean that the last valid address that can
use R1 as a base is dummy+5999.
- If the previous item is true then the LG of FAR3 at location x'C' should not
successfully assemble because FAR3 is at DUMMY+6000.
- Even if there is a confusion between "1 byte prior to the specified end" vs.
"the specified end", the LG for FAR4 at location x'12' should certainly fail.
Since the LG of FAR4 didn't fail, my understanding of the function of the 'end'
specification must be a misunderstanding. Can anyone offer any clarity?
Thanks.
- mb
