Restrictions

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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.

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No_Abort_Statements

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No_Dispatch

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No_Local_Protected_Objects

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No_Requeue

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No_Task_Attributes

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No_Task_Hierarchy

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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.

Updated May 11, 2005
Copyright XGC Software