DXD instruction
The DXD instruction identifies and defines an external dummy section. See also External dummy sections.
- symbol
- Is an external symbol which 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
- duplication_factor
- Is the duplication factor subfield equivalent to the duplication factor subfield of the DS instruction.
- type
- Is the type subfield equivalent to the type subfield of the DS instruction.
- type_extension
- Is the type extension subfield equivalent to the type extension subfield of the DS instruction.
- modifiers
- Is the modifiers subfield equivalent to the modifiers subfield of the DS instruction.
- nominal_value
- Is the nominal-value subfield equivalent to the nominal-value subfield of the DS instruction. The nominal value is optional. If specified, it is not generated.
The DXD instruction can be used anywhere in a source module, after the ICTL instruction.
In order to reference the storage defined by the external dummy section, the ordinary symbol denoted by symbol must appear in the operand of a Q-type constant. This symbol represents the address of the first byte of the external dummy section defined, and has a length attribute value of 1.
The subfields in the operand field (duplication factor, type, type extension, modifier, and nominal value) are specified in the same way as in a DS instruction. The assembler computes the amount of storage and the alignment required for an external dummy section from the area specified in the operand field. For more information about how to specify the subfields, see DS instruction.
A DXD CL20 20 bytes, byte alignment
B DXD 3F,XL4 20 bytes, fullword alignment
C DXD LQ 16 bytes, quadword alignment
- The DSECT instruction also defines an external dummy section, but only if the symbol in the name field appears in a Q-type offset constant in the same source module. Otherwise, a DSECT instruction defines a dummy section.
- If two or more external dummy sections for different source modules have the same name, the linker uses the most restrictive alignment, and the largest section to compute the total length.