Relocatable terms
A term is relocatable if its value changes upon program relocation.
A term is relocatable if its value changes upon program relocation. The value of a relocatable term depends on the location of the control section containing it. If the control section moves to a different storage location (for example, a csect is relocated by the binder at bind time), the value of the relocatable term changes accordingly.
A relocatable term is one of the following items:
- A label defined within a csect that does not have TD or TC as its Storage Mapping Class (SMC)
- A symbol set to a relocatable expression
- A label defined within a dsect
- A dsect name
- A location counter reference (which uses $, the dollar sign)
If it is not used as a displacement for a D-form instruction, the value of a csect label or a location counter reference is its relocatable address, which is the sum of the containing csect address and the offset relative to the containing csect. If it is used as a displacement for a D-form instruction, the assembler implicitly subtracts the containing csect address so that only the the offset is used for the displacement. A csect address is the offset relative to the beginning of the first csect of the file.
A dsect is a reference control section that allows you to describe the layout of data in a storage area without actually reserving any storage. A dsect provides a symbolic format that is empty of data. The assembler does assign location counter values to the labels that are defined in a dsect. The values are the offsets relative to the beginning of the dsect. The data in a dsect at run time can be referenced symbolically by using the labels defined in a dsect.
Relocatable terms based on a dsect location counter (either the dsect name or dsect labels) are meaningful only in the context of a .using statement. Since this is the only way to associate a base address with a dsect, the addressability of the dsect is established in combination with the storage area.
A relocatable term may be based on any control section, either csect or dsect, in all the contexts except if it is used as a relocatable address constant. If a csect label is used as an address constant, it represents a relocatable address, and its value is the offset relative to the csect plus the address of the csect. A dsect label cannot be used as a relocatable address constant since a dsect is only a data template and has no address.
If two dsect labels are defined in the same dsect, their difference can be used as an absolute address constant.