HLASM Language Reference

| You may declare other classes in addition to the defaults, but the resulting program
| object will not be convertible to a load module.
| Parts (MVS and CMS)
| Parts are the smallest externally named and independently relocatable subdivisions
| of elements in a merge class. A class containing parts may contain only parts, and
| a class containing anything other than parts may not contain any parts.
| ENTRY statements may not define an entry point in a part.
| You define a part with the CATTR instruction, which must follow the initiation of an
| executable section. The name of the class to which the part belongs is provided in
| the name entry of the CATTR instruction, and the name of the part is specified as
| an operand. The first definition of a class name may also specify the attributes of
| the class. (See “CATTR Instruction (MVS and CMS)” on page 112 for further
| information.)
| For example, suppose you define two parts in a class:
| SECT_B CSECT , Define section SECT_B
| PClass CATTR Part(Part_R),RMODE(ANY) Define class PClass, part Part_R
| - - - Statements included in Part_R
| PClass CATTR Part(Part_S) Define part Part_S in class PClass
| - - - Statements included in Part_S
| PClass CATTR Part(Part_R) Resume class PClass and part Part_R
| - - - More statements included in Part_R
| These statements define a “merge” class PClass containing two parts, Part_R and
| Part_S. If other classes or other object files declare parts with the same names in
| the same class, the binder will merge their contents to determine the final part
| definition in the program object.
| You may provide additional statements for a part by specifying a CATTR statement
| with the class name in the name entry and the part name specified as the operand.
| No other class attributes may be specified following the first CATTR statement
| declaring the class.
| Parts are automatically assigned a “merge” attribute, meaning that more than one
| identically named part may appear in a class defined in other assemblies or
| compilations. The binder will assign the longest length and strictest alignment of all
| such identically-named parts, and will merge the machine language text
| contributions of each to form the final text belonging to that part. The order of text
| merging depends on the sequence of parts processing by the binder.
| Note: During linking, parts may be arranged in any order, depending on their
| priority attribute. Do not assume any ordering relationship among parts.
Location Counter Setting
| The assembler maintains a separate location counter for each section, element,
| and part. The location counter setting for the first section starts at 0, except when
| an initial section is started with a START instruction that specifies a nonzero
| location counter value. The location values assigned to the instructions and other
| data in a section, element, or part are, therefore, relative to the location counter
| setting at the beginning of that section, element, or part.
Chapter 3. Program Structures and Addressing 61