Ada Bare Bones: Difference between revisions

===Exception handling===

I have based my knowledge of this kind of work on GNAT's High Integrity Edition manual, in which is hints that at this level of work, a programmer should be able to declare their own exceptions and be able to raise them. I have had it confirmed via a [http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53684 bug I filed] that this is not the case. Any attempt to do this requests that a package from the RTS called Ada.Exceptions be present, I have experimented by creating a version of this package:

<source lang="ada">

with System;

package Ada.Exceptions is

pragma Preelaborate (Exceptions);

type Exception_Id is private;

pragma Preelaborable_Initialization (Exception_Id);

Null_Id : constant Exception_Id;

procedure Raise_Exception

(E : Exception_Id;

Message : String := "");

pragma No_Return (Raise_Exception);

private

type Exception_Id is new Natural;

Null_Id : constant Exception_Id := Exception_Id'First;

end Ada.Exceptions;

with GNAT.Source_Info;

with Last_Chance_Handler;

package body Ada.Exceptions is

procedure Raise_Exception

(E : Exception_Id;

Message : String := "") is

pragma Unreferenced (E);

pragma Unreferenced (Message);

File : String := GNAT.Source_Info.File;

Line : Positive := GNAT.Source_Info.Line;

Source_Location : String := GNAT.Source_Info.Source_Location;

Enclosing_Entity : String := GNAT.Source_Info.Enclosing_Entity;

pragma Unreferenced (File, Line, Source_Location, Enclosing_Entity);

begin

Last_Chance_Handler (System.Null_Address, 0);

loop

null;

end loop;

end Raise_Exception;

end Ada.Exceptions;

</source>

This seemed to work until I tried to catch the exception inside bare_bones.adb at which point the compiler threw up a number of warnings, resulting in a compile failure:

<pre>

bare_bones.adb:23:17: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:23:17: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:30:07: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:30:07: warning: Last_Chance_Handler will be called on exception

bare_bones.adb:33:17: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:33:17: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:38:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:38:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:44:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:44:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:50:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:50:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:56:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:56:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:61:42: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:61:42: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:86:21: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:86:21: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:86:30: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:86:30: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:86:39: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:86:39: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:89:26: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:89:26: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:97:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:97:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:104:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:104:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:110:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:110:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:124:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:124:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:130:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:130:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:136:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:136:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:142:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:142:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:148:20: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:148:20: warning: "Constraint_Error" may call Last_Chance_Handler

bare_bones.adb:151:04: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:151:04: warning: Last_Chance_Handler will be called on exception

bare_bones.adb:160:04: warning: pragma Restrictions (No_Exception_Propagation) in effect

bare_bones.adb:160:04: warning: this handler can never be entered, and has been removed

bare_bones.adb:160:09: violation of restriction "No_Exception_Propagation" at ../gnat.adc:10

gnatmake: "/home/laguest/src/mine/bare_bones/src/bare_bones.adb" compilation error

make: *** [disk/boot/bare_bones] Error 4

</pre>

So the net effect of this is to not bother with this package and only use the language defined exceptions for bare metal programming.