Restrictions and Profiles

This page defines how the Ada 95 restrictions, accessible through the pragma Restrictions, are supported. Unsafe features such as run-time dispatching and heap management are not supported in the run-time system, so all the restrictions that are relevant for these features are set to True by default.

The following restrictions are built in. That is, they cannot be turned off and are exploited by the compiler to offer better-quality generated code than would otherwise be possible.

No_Abort_Statements
No_Dispatch
No_Local_Protected_Objects
No_Requeue
No_Task_Attributes
No_Task_Hierarchy
No_Terminate_Alternatives

The implementation-defined pragma Profile may also be used to set and unset restrictions that correspond to a certain application area. The profiles supported are as follows:

Table B-1. Supported Profiles

Profile Name	Description
XGC	This is the default profile and offers the least restrictions.
Ravenscar	This allows a limited form of tasking that includes static tasks, protected objects, the delay until statement and interrupts.
Restricted_Run_Time	This severely restricts the use of non-deterministic language features (including tasking) and is suitable for general avionics applications.
No_Run_Time	This profile prohibits all calls to the predefined Ada library and is useful for safety-critical applications. Calls to the compiler support library are not restricted.

Table B-2 gives the individual restrictions for each profile. Note that the built-in restrictions apply to all profiles.

Table B-2. Profiles and Restrictions

Restriction	Ada 95 Reference Manual Section	Default	Ravenscar	Restricted_ Run_Time
Boolean_Entry_Barriers	XGC (Ravenscar)	False	True	True
Immediate_Reclamation	RM H.4(10)	False	False	False
No_Abort_Statements	RM D.7(5), H.4(3)	True	True	True
No_Access_Subprograms	RM H.4(17)	False	True	True
No_Allocators	RM H.4(7)	False	False	True
No_Asynchronous_Control	RM D.9(10)	False	True	True
No_Calendar	XGC	False	True	True
No_Delay	RM H.4(21)	False	False	True
No_Dispatch	RM H.4(19)	True	True	True
No_Dynamic_Interrupts	XGC	True	True	True
No_Dynamic_Priorities	RM D.9(9)	False	True	True
No_Elaboration_Code	XGC	False	False	True
No_Entry_Calls_In_Elaboration_Code	XGC	False	True	True
No_Entry_Queue	XGC	True	True	True
No_Enumeration_Maps	XGC	False	False	True
No_Exception_Handlers	XGC	False	False	True
No_Exceptions	RM H.4(12)	False	False	False
No_Fixed_Point	RM H.4(15)	False	False	False
No_Floating_Point	RM H.4(14)	False	False	False
No_Implementation_Attributes	XGC	False	False	True
No_Implementation_Pragmas	XGC	False	False	True
No_Implementation_Restrictions	XGC	False	False	True
No_Implicit_Conditionals	XGC	False	False	True
No_Implicit_Heap_Allocations	RM D.8(8), H.4(3)	False	True	True
No_Implicit_Loops	XGC	False	False	False
No_IO	RM H.4(20)	False	True	True
No_Local_Allocators	RM H.4(8)	False	True	True
No_Local_Protected_Objects	XGC	True	True	True
No_Nested_Finalization	RM D.7(4)	True	True	True
No_Protected_Type_Allocators	XGC	True	True	True
No_Protected_Types	RM H.4(5)	False	False	True
No_Recursion	RM H.4(22)	False	True	True
No_Reentrancy	RM H.4(23)	False	False	False
No_Relative_Delay	XGC	False	True	True
No_Requeue	XGC	True	True	True
No_Select_Statements	XGC (Ravenscar)	False	True	True
No_Standard_Storage_Pools	XGC	True	True	True
No_Streams	XGC	True	True	True
No_Task_Allocators	RM D.7(7)	False	True	True
No_Task_Attributes	XGC	True	True	True
No_Task_Hierarchy	RM D.7(3), H.4(3)	True	True	True
No_Task_Termination	XGC	True	True	True
No_Terminate_Alternatives	RM D.7(6)	True	True	True
No_Unchecked_Access	RM H.4(18)	False	True	True
No_Unchecked_Conversion	RM H.4(16)	False	False	True
No_Unchecked_Deallocation	RM H.4(9)	True	True	True
No_Wide_Characters	XGC	False	True	True
Static_Priorities	XGC	False	True	True
Static_Storage_Size	XGC	False	True	True

Table B-3 gives the restrictions concerning numerical limits.

Table B-3. Profiles and Numerical Restrictions

Restriction	Ada 95 Reference Manual Section	Default	Ravenscar	Restricted_ Run_Time
Max_Asynchronous_Select_Nesting	RM D.7(18), H.4(2)	0	0	0
Max_Protected_Entries	RM D.7(14)	1	1	1
Max_Select_Alternatives	RM D.7(12)	Undefined	0	0
Max_Storage_At_Blocking	RM D.7(17)	0	0	0
Max_Task_Entries	RM D.7(13), H.4(2)	Undefined	0	0
Max_Tasks	RM D.7(19), H.4(2)	Undefined	Undefined	Undefined
Max_Entry_Queue_Depth	Ravenscar specific	1	1	1

Violation of the restriction Max_Entry_Queue_Depth is detected at run time and raises the predefined exception Program_Error.

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