HLASM Language Reference

USING Instruction
If register 0 is used as a base register, the referenced control section (or dummy
section) is not relocatable, despite the fact that operand base may be relocatable.
The control section can be made relocatable by:
Replacing register 0 in the USING statement
Loading the new register with a relocatable value
Reassembling the program
Range of an Ordinary USING Instruction
The range of an ordinary USING instruction (called the ordinary USING range, or
simply the USING range) is the 4096 bytes beginning at the base address specified
in the USING instruction, or the range as specified by the range end, whichever is
| the lesser. For long-displacement instructions, the range is the addresses between
| (base_address-524288) and (base_address+524287). Addresses that lie within the
USING range can be converted from their implicit to their explicit
base-displacement form using the designated base registers; those outside the
USING range cannot be converted.
The USING range does not depend upon the position of the USING instruction in
the source module; rather, it depends upon the location of the base address
specified in the USING instruction.
The USING range is the range of addresses in a control section that is associated
with the base register specified in the USING instruction. If the USING instruction
assigns more than one base register, the composite USING range is the union of
the USING ranges that would apply if the base registers were specified in separate
USING instructions.
| Note that USING ranges need not be contiguous. For example, you could specify
| USING X,4
| USING X+6,5
| and implicit addresses with values between X+4096 and X+5999 would not be
| addressable by instructions with unsigned 12-bit displacements.
Two USING ranges coincide when the same base address is specified in two
different USING instructions, even though the base registers used are different.
When two USING ranges coincide, the assembler uses the higher-numbered
register for assembling the addresses within the common USING range. In effect,
the domain of the USING instruction that specifies the lower-numbered register is
ended by the other USING instruction. If the domain of the USING instruction that
specifies the higher-number register is subsequently terminated, the domain of the
other USING instruction is resumed.
Two USING ranges overlap when the base address of one USING instruction lies
within the range of another USING instruction. You can use the WARN suboption
of the USING assembler option to find out if you have any overlapping USING
ranges. When an overlap occurs the assembler issues a diagnostic message.
However, the assembler does allow an overlap of one byte in USING ranges so
that you don't receive a diagnostic message if you code the following statements:
PSTART CSECT
LR R12,R15
LA R11,495(,R12)
USING PSTART,R12
USING PSTART+495,R11
222 HLASM V1R5 Language Reference