Ada 2012 Reference Manual

J.15.3 Pragma Pack

The form of a pragma Pack, which is a representation pragma (see 13.1), is as follows:

pragma Pack (first_subtype_local_name);

The first_subtype_local_name of a pragma Pack shall denote a composite subtype.

Pragma Pack specifies that the Pack aspect (see 13.2) for the type denoted by first_subtype_local_name has the value True.