HLASM Language Reference

DSECT Instruction
– An ordinary or labeled USING statement that specifies both a general
register that the assembler can use as a base register for the dummy
section, and a value from the dummy section that the assembler may
assume the register contains, or
– A dependent or labeled dependent USING statement that specifies a
supporting base address (for which there is a corresponding ordinary
USING statement) that lets the assembler determine a base register and
displacement for the dummy section, and a value from the dummy section
that the assembler may assume is the same as the supporting base
address
Ensure that the base register is loaded with either:
– The actual address of the storage area if an ordinary USING statement or a
labeled USING statement was specified, or
– The base address specified in the corresponding ordinary USING statement
if a dependent or labeled dependent USING statement was specified.
The values assigned to symbols defined in a dummy section are relative to the
initial statement of the section. Thus, all machine instructions that refer to names
defined in the dummy section refer, at execution time, to storage locations relative
to the address loaded into the register.
Figure 54 shows an example of how to code the DSECT instruction. The sample
code is referred to as “Assembly-2.”
Assume that two independent assemblies (Assembly-1 and Assembly-2) have been
loaded and are to be run as a single overall program. Assembly-1 is a routine that
1. Places a record in an area of storage
2. Places the address of the storage area in general register 3
3. Branches to Assembly-2 to process the record
The storage area from Assembly-1 is identified in Assembly-2 by the dummy
control section (DSECT) named INAREA. Parts of the storage area that you want
to work with are named INCODE, OUTPUTA, and OUTPUTB. The statement
USING INAREA,3 assigns general register 3 as the base register for the INAREA
DSECT. General register 3 contains the address of the storage area. Because the
symbols in the DSECT are defined relative to the beginning of the DSECT, the
address values they represent are, at the time of program execution, the actual
storage locations of the storage area that general register 3 addresses.
Chapter 5. Assembler Instruction Statements 179