LOCTR instruction

The LOCTR instruction specifies multiple location counters within a control section. The assembler assigns consecutive addresses to the segments of code using one location counter before it assigns addresses to segments of coding using the next location counter.


>>-symbol--LOCTR-----------------------------------------------><

symbol

Is one of the following:

An ordinary symbol
A variable symbol that has been assigned a character string with a value that is valid for an ordinary symbol

By using the LOCTR instruction, you can code your control section in a logical order. For example, you can code work areas and data constants within the section of code, using them without having to branch around them:

A      CSECT ,          See note 1
       LR    12,15
       USING A,12
       .
B      LOCTR ,          See note 2
       .
C      LOCTR ,
       .
B      LOCTR ,          See note 3
       .
A      LOCTR ,          See note 4
       .
DUM    DSECT ,          See note 1
C      LOCTR ,          See note 5
       .
       END

LOCTRs are ordered by their definition order. So in the previous example, the ordering is A, B, and C. When there are statements in LOCTR groups, the code is generated using currently active USINGs and then moved to the final location.

Notes:

The first location counter of a section, class, or part is defined by the name of the START, CSECT, DSECT, RSECT, CATTR, or COM instruction defining the section.
The LOCTR instruction defines a location counter.
The LOCTR continues a previously defined location counter. A location counter remains in use until it is interrupted by a LOCTR, CSECT, DSECT, RSECT, or COM instruction.
A LOCTR instruction with the same name as a control section continues the first location counter of that section. However, an unnamed LOCTR cannot be used to continue an unnamed (private code) control section.
A LOCTR instruction with the same name as a LOCTR instruction in a previous control section causes that control section to be continued using the location counter specified, even though the LOCTR instruction might follow the definition (or resumption) of a different section.
To continue a location counter in an unnamed section, a named location counter must first be specified for the section by a LOCTR in the unnamed section.

A control section cannot have the same name as a previous LOCTR instruction. A LOCTR instruction placed before the first control section definition initiates an unnamed control section before the LOCTR instruction is processed.

The length attribute of a LOCTR name is 1.

LOCTR instructions do not force alignment; code assembled under a location counter other than the first location counter of a control section is assembled starting at the next available byte after the previous segment.

A LOCTR name can be referenced as an ordinary symbol. If the LOCTR name does not match a section name, its value is the location counter value assigned to its first appearance, and it might have arbitrary alignment and other attributes. If the LOCTR name is also a control section name, the value assigned is that of the origin of the control section. So a LOCTR with the same name as the CSECT resumes the first location counter within the CSECT. A CSECT instruction resumes the last location counter used.

Table 1. LOCTR behavior with NOGOFF option
LOCTR name	Effect
Section	Resumes assembling with the first location counter of that section
Other	If the LOCTR name was previously declared, resumes assembling with the location counter of that LOCTR group If the LOCTR name was not previously declared, begins processing a new LOCTR group of statements to be assembled following the most recently processed section or LOCTR group

Table 2. LOCTR behavior with GOFF option
LOCTR name	Effect
Section	Resumes assembling with the first location counter of the element in the `B_TEXT` class of that section
Class	Not allowed
Part	Resumes assembling with the first location counter of the part
Other	If the LOCTR name was previously declared, resumes assembling with the location counter of that LOCTR group If the LOCTR name was not previously declared, begins processing statements in a new LOCTR group to be assembled following the most recently processed class, part, or LOCTR group.