Ada Bare Bones: Difference between revisions
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(Removed incorrect information regarding user-defined exceptions.) |
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====No_Exception_Propagation==== |
====No_Exception_Propagation==== |
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This forces the compiler to disallow any attempt to raise an exception over a subprogram boundary. |
This directive forces the compiler to disallow any attempt to raise an exception over a subprogram boundary. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fException_005fPropagation.html#No_005fException_005fPropagation GNAT RM:No_Exception_Propagation] for more information. |
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The [http://docs.adacore.com/gnat-hie-docs/html/gnathie_ug_3.html#SEC8 GNAT High Integrity Edition] documentation states the |
Note: The [http://docs.adacore.com/gnat-hie-docs/html/gnathie_ug_3.html#SEC8 GNAT High Integrity Edition] documentation states the following: |
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<blockquote> |
<blockquote> |
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Exception declarations and raise statements are still permitted under this restriction. A raise statement is compiled into a call of __gnat_last_chance_handler. |
Exception declarations and raise statements are still permitted under this restriction. A raise statement is compiled into a call of <tt>__gnat_last_chance_handler</tt>. |
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</blockquote> |
</blockquote> |
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All exceptions that are not handled with an explicit exception handler within its subprogram will be caught with the <tt>Last_Chance_Handler</tt> subprogram. This will cause a warning to be issued at compile time. |
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I have been unable, thus far, to raise my own exceptions, although I can declare one at library level. On placing a declaration inside console.ads: |
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<source lang="ada"> |
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TE : exception; -- A badly named exception. |
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</source> |
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and raising inside bare_bones.adb: |
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<source lang="ada"> |
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raise Console.TE; |
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exception |
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when Console.TE => |
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Put ("TE caught", 1, 2); |
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</source> |
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and upon compiling, I get the following: |
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<pre> |
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bare_bones.adb:17:04: construct not allowed in configurable run-time mode |
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bare_bones.adb:17:04: file a-except.ads not found |
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bare_bones.adb:17:04: entity "Ada.Exceptions.Raise_Exception" not available |
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gnatmake: "/home/laguest/src/mine/bare_bones/src/bare_bones.adb" compilation error |
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make: *** [disk/boot/bare_bones] Error 4 |
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</pre> |
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so the compiler is looking for the Ada.Exceptions package which defines the normal language standard exception handling, not the cut down version we are using here. Do the same with one of the language defined exceptions works fine. ''I will file a bug at FSF for this as I believe it to be incorrect''. |
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I have had it confirmed via a [http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53684 bug I filed] that the programmer is not allowed to declare their own exceptions and catch them. I have experimented by creating a version of the Ada.Exceptions (a-except.ad[sb]) package: |
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<source lang="ada"> |
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with System; |
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package Ada.Exceptions is |
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pragma Preelaborate (Exceptions); |
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type Exception_Id is private; |
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pragma Preelaborable_Initialization (Exception_Id); |
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Null_Id : constant Exception_Id; |
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procedure Raise_Exception |
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(E : Exception_Id; |
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Message : String := ""); |
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pragma No_Return (Raise_Exception); |
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private |
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type Exception_Id is new Natural; |
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Null_Id : constant Exception_Id := Exception_Id'First; |
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end Ada.Exceptions; |
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with GNAT.Source_Info; |
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with Last_Chance_Handler; |
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package body Ada.Exceptions is |
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procedure Raise_Exception |
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(E : Exception_Id; |
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Message : String := "") is |
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pragma Unreferenced (E); |
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pragma Unreferenced (Message); |
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File : String := GNAT.Source_Info.File; |
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Line : Positive := GNAT.Source_Info.Line; |
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Source_Location : String := GNAT.Source_Info.Source_Location; |
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Enclosing_Entity : String := GNAT.Source_Info.Enclosing_Entity; |
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pragma Unreferenced (File, Line, Source_Location, Enclosing_Entity); |
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begin |
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Last_Chance_Handler (System.Null_Address, 0); |
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loop |
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null; |
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end loop; |
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end Raise_Exception; |
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end Ada.Exceptions; |
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</source> |
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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: |
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<pre> |
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bare_bones.adb:23:17: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:23:17: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:30:07: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:30:07: warning: Last_Chance_Handler will be called on exception |
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bare_bones.adb:33:17: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:33:17: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:38:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:38:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:44:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:44:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:50:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:50:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:56:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:56:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:61:42: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:61:42: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:86:21: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:86:21: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:86:30: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:86:30: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:86:39: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:86:39: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:89:26: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:89:26: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:97:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:97:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:104:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:104:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:110:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:110:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:124:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:124:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:130:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:130:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:136:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:136:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:142:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:142:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:148:20: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:148:20: warning: "Constraint_Error" may call Last_Chance_Handler |
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bare_bones.adb:151:04: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:151:04: warning: Last_Chance_Handler will be called on exception |
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bare_bones.adb:160:04: warning: pragma Restrictions (No_Exception_Propagation) in effect |
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bare_bones.adb:160:04: warning: this handler can never be entered, and has been removed |
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bare_bones.adb:160:09: violation of restriction "No_Exception_Propagation" at ../gnat.adc:10 |
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gnatmake: "/home/laguest/src/mine/bare_bones/src/bare_bones.adb" compilation error |
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make: *** [disk/boot/bare_bones] Error 4 |
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</pre> |
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So the net effect of this is to not bother with this package and only use the language defined exceptions for bare metal programming. |
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====No_Exception_Registration==== |
====No_Exception_Registration==== |
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