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H.4 Safety and Security Restrictions

  1. This clause defines restrictions that can be used with pragma Restrictions, See section 13.12 Pragma Restrictions, these facilitate the demonstration of program correctness by allowing tailored versions of the run-time system.

    Static Semantics

  2. The following restrictions, the same as in See section D.7 Tasking Restrictions, apply in this Annex: No_Task_Hierarchy, No_Abort_Statement, No_Implicit_Heap_Allocation, Max_Task_Entries is 0, Max_Asynchronous_Select_Nesting is 0, and Max_Tasks is 0. The last three restrictions are checked prior to program execution.
  3. The following additional restrictions apply in this Annex.
  4. Tasking-related restriction:
  5. No_Protected_Types
    There are no declarations of protected types or protected
  6. Memory-management related restrictions:
  7. No_Allocators
    There are no occurrences of an allocator.
  8. No_Local_Allocators
    Allocators are prohibited in subprograms, generic sub-programs,
    tasks, and entry bodies; instantiations of generic
    packages are also prohibited in these contexts.
  9. No_Unchecked_Deallocation
    Semantic dependence on Unchecked_Deallocation is not allowed.
  10. Immediate_Reclamation
    Except for storage occupied by objects created by allocators
    and not deallocated via unchecked deallocation, any storage
    reserved at run time for an object is immediately reclaimed
    when the object no longer exists.
  11. Exception-related restriction:
  12. No_Exceptions
    Raise_statements and exception_handlers are not allowed. No
    language-defined run-time checks are generated; however, a
    run-time check performed automatically by the hardware is
  13. Other restrictions:
  14. No_Floating_Point
    Uses of predefined floating point types and operations, and
    declarations of new floating point types, are not allowed.
  15. No_Fixed_Point
    Uses of predefined fixed point types and operations, and
    declarations of new fixed point types, are not allowed.
  16. No_Unchecked_Conversion
    Semantic dependence on the predefined generic
    Unchecked_Conversion is not allowed.
  17. No_Access_Subprograms
    The declaration of access-to-subprogram types is not allowed.
  18. No_Unchecked_Access
    The Unchecked_Access attribute is not allowed.
  19. No_Dispatch
    Occurrences of T'Class are not allowed, for any (tagged)
    subtype T.
  20. No_IO
    Semantic dependence on any of the library units
    Sequential_IO, Direct_IO, Text_IO, Wide_Text_IO, or Stream_IO
    is not allowed.
  21. No_Delay
    Delay_Statements and semantic dependence on package Calendar
    are not allowed.
  22. No_Recursion
    As part of the execution of a subprogram, the same subprogram
    is not invoked.
  23. No_Reentrancy
    During the execution of a subprogram by a task, no other task
    invokes the same subprogram.

    Implementation Requirements

  24. If an implementation supports pragma Restrictions for a particular argument, then except for the restrictions No_Unchecked_Deallocation, No_Unchecked_Conversion, No_Access_Subprograms, and No_Unchecked_Access, the associated restriction applies to the run-time system.

    Documentation Requirements

  25. If a pragma Restrictions(No_Exceptions) is specified, the implementation shall document the effects of all constructs where language-defined checks are still performed automatically (for example, an overflow check performed by the processor).

    Erroneous Execution

  26. Program execution is erroneous if pragma Restrictions(No_Exceptions) has been specified and the conditions arise under which a generated language-defined run-time check would fail.
  27. Program execution is erroneous if pragma Restrictions(No_Recursion) has been specified and a subprogram is invoked as part of its own execution, or if pragma Restrictions(No_Reentrancy) has been specified and during the execution of a subprogram by a task, another task invokes the same subprogram.

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