HLASM Language Reference

USING Instruction
base
specifies a base address, which must be a relocatable expression. The value
of the expression must lie between 0 and 2 31 −1.
address
is a simply relocatable expression that represents an implicit address within the
| range of an active USING instruction. The range of an active USING is
| considered to be that which is valid for generating 12-bit or 20-bit
| displacements.
end
specifies the end address, which can be a relocatable or an absolute
expression. The value of the expression must lie between 0 and 2 31 −1. The
end address may exceed the (base address + default range) without error. The
end address must be greater than the base and must have the same
relocatability attributes.
The implicit address denoted by address specifies the address where base is to be
based, and is known as the supporting base address. As address is a relocatable
expression, it distinguishes a dependent USING from an ordinary USING. The
assembler converts the implicit address denoted by address into its explicit
base-displacement form. It then assigns the base register from this explicit address
as the base register for base. The assembler assumes that the base register
contains the base address base minus the displacement determined in the explicit
address. The assembler also assumes that address is appropriately aligned for the
code based on base. Warnings are not issued for potential alignment problems in
the dependent USING address.
A dependent USING depends on the presence of one or more corresponding
labeled or ordinary USINGs being in effect to resolve the symbolic expressions in
the range of the dependent USING.
The following example shows the use of an unlabeled dependent USING:
EXAMPLE CSECT
USING EXAMPLE,R1,R11 Ordinary USING
.
.
USING IHADCB,DCBUT2 Unlabeled dependent USING
LH R,DCBBLKSI Uses R1 or R11 for BASE
.
.
DCBUT2 DCB DDNAME=SYSUT2,...
The following example shows the use of two labeled dependent USINGs:
EXAMPLE CSECT
USING EXAMPLE,R1,R11 Ordinary USING
.
.
DCB1 USING IHADCB,DCBUT1 Labeled dependent USING
DCB2 USING IHADCB,DCBUT2 Labeled dependent USING
MVC DCB2.DCBBLKSI,DCB1.DCBBLKSI Uses R1 or R11 for BASE
.
.
DCBUT1 DCB DDNAME=SYSUT1,...
DCBUT2 DCB DDNAME=SYSUT2,...
Chapter 5. Assembler Instruction Statements 227