[Ada] Imported C++ exceptions

Arnaud Charlet charlet@adacore.com
Mon Oct 14 13:34:00 GMT 2013


It is now possible to import C++ exceptions and to handle it.
The following program will display: Got Cpp exception
It can be built using the following project file:

project except is
  for Languages use ("Ada", "C++");
  for Main use ("main.adb");
end except;

package Cppexcept is
   Cpp_Int_Exception : exception;
   pragma Import (Cpp, Cpp_Int_Exception, "_ZTIi");
end Cppexcept;

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Exceptions; use Ada.Exceptions;
with Cppexcept; use Cppexcept;

procedure Main is
   procedure Raise_Excep_Int;
   pragma Import (C, Raise_Excep_Int);
   --  Raise a Cpp exception
begin
   Raise_Excep_Int;
exception
   when Cpp_Int_Exception =>
      Put_Line ("Got Cpp exception");
   when X: others =>
      Put_Line ("Err, got unexpected exception: "
                & Exception_Information (X));
end Main;

extern "C" void raise_excep_int (void)
{
  throw 2;
}

Tested on x86_64-pc-linux-gnu, committed on trunk

2013-10-14  Tristan Gingold  <gingold@adacore.com>

	* sem_prag.adb (Process_Import_Or_Interface): Allow importing
	of exception using convention Cpp.
	* exp_prag.adb (Expand_Pragma_Import_Or_Interface): Expand cpp
	imported exceptions.
	* raise-gcc.c (is_handled_by): Filter C++ exception occurrences.
	* gnat_rm.texi: Document how to import C++ exceptions.

-------------- next part --------------
Index: exp_prag.adb
===================================================================
--- exp_prag.adb	(revision 203544)
+++ exp_prag.adb	(working copy)
@@ -575,6 +575,64 @@
          if No (Init_Call) and then Present (Expression (Parent (Def_Id))) then
             Set_Expression (Parent (Def_Id), Empty);
          end if;
+      elsif Ekind (Def_Id) = E_Exception
+        and then Convention (Def_Id) = Convention_CPP
+      then
+
+         --  Import a C++ convention
+
+         declare
+            Loc            : constant Source_Ptr := Sloc (N);
+            Exdata         : List_Id;
+            Lang_Char      : Node_Id;
+            Foreign_Data   : Node_Id;
+            Rtti_Name      : constant Node_Id := Arg3 (N);
+            Dum            : constant Entity_Id  := Make_Temporary (Loc, 'D');
+
+         begin
+            Exdata := Component_Associations (Expression (Parent (Def_Id)));
+
+            Lang_Char := Next (First (Exdata));
+
+            --  Change the one-character language designator to 'C'
+
+            Rewrite (Expression (Lang_Char),
+              Make_Character_Literal (Loc,
+                Chars => Name_uC,
+                Char_Literal_Value =>
+                  UI_From_Int (Character'Pos ('C'))));
+            Analyze (Expression (Lang_Char));
+
+            --  Change the value of Foreign_Data
+
+            Foreign_Data := Next (Next (Next (Next (Lang_Char))));
+
+            Insert_Actions (Def_Id, New_List (
+              Make_Object_Declaration (Loc,
+                Defining_Identifier => Dum,
+                Object_Definition   =>
+                  New_Occurrence_Of (Standard_Character, Loc)),
+
+              Make_Pragma (Loc,
+                Chars                        => Name_Import,
+                Pragma_Argument_Associations => New_List (
+                  Make_Pragma_Argument_Association (Loc,
+                    Expression => Make_Identifier (Loc, Name_Ada)),
+
+                  Make_Pragma_Argument_Association (Loc,
+                    Expression => Make_Identifier (Loc, Chars (Dum))),
+
+                  Make_Pragma_Argument_Association (Loc,
+                    Chars => Name_Link_Name,
+                    Expression => Relocate_Node (Rtti_Name))))));
+
+            Rewrite (Expression (Foreign_Data),
+              Unchecked_Convert_To (Standard_A_Char,
+                Make_Attribute_Reference (Loc,
+                  Prefix         => Make_Identifier (Loc, Chars (Dum)),
+                  Attribute_Name => Name_Address)));
+            Analyze (Expression (Foreign_Data));
+         end;
       end if;
    end Expand_Pragma_Import_Or_Interface;
 
Index: gnat_rm.texi
===================================================================
--- gnat_rm.texi	(revision 203543)
+++ gnat_rm.texi	(working copy)
@@ -11963,6 +11963,7 @@
 @emph{Exception_Name:} nnnnn
 @emph{Message:} mmmmm
 @emph{PID:} ppp
+@emph{Load address:} 0xhhhh
 @emph{Call stack traceback locations:}
 0xhhhh 0xhhhh 0xhhhh ... 0xhhh
 @end smallexample
@@ -11984,10 +11985,12 @@
 not making use of this field.
 
 @item
-The Call stack traceback locations line and the following values
-are present only if at least one traceback location was recorded.
-The values are given in C style format, with lower case letters
-for a-f, and only as many digits present as are necessary.
+The Load address line, the Call stack traceback locations line and the
+following values are present only if at least one traceback location was
+recorded. The Load address indicates the address at which the main executable
+was loaded; this line may not be present if operating system hasn't relocated
+the main executable. The values are given in C style format, with lower case
+letters for a-f, and only as many digits present as are necessary.
 @end itemize
 
 @noindent
@@ -18874,6 +18877,19 @@
 contains @samp{Foreign_Exception}. Finalization and awaiting dependent
 tasks works properly when such foreign exceptions are propagated.
 
+It is also possible to import a C++ exception using the following syntax:
+
+@smallexample @c ada
+LOCAL_NAME : exception;
+pragma Import (Cpp,
+  [Entity =>] LOCAL_NAME,
+  [External_Name =>] static_string_EXPRESSION);
+@end smallexample
+
+@noident
+The @code{External_Name} is the name of the C++ RTTI symbol. You can then
+cover a specific C++ exception in an exception handler.
+
 @node Interfacing to COBOL
 @section Interfacing to COBOL
 
Index: raise-gcc.c
===================================================================
--- raise-gcc.c	(revision 203538)
+++ raise-gcc.c	(working copy)
@@ -87,6 +87,36 @@
 #define CXX_EXCEPTION_CLASS 0x474e5543432b2b00ULL
 #define GNAT_EXCEPTION_CLASS 0x474e552d41646100ULL
 
+/* Structure of a C++ exception, represented as a C structure...  See
+   unwind-cxx.h for the full definition.  */
+
+struct __cxa_exception
+{
+  void *exceptionType;
+  void (*exceptionDestructor)(void *);
+
+  void (*unexpectedHandler)();
+  void (*terminateHandler)();
+
+  struct __cxa_exception *nextException;
+
+  int handlerCount;
+
+#ifdef __ARM_EABI_UNWINDER__
+  struct __cxa_exception* nextPropagatingException;
+
+  int propagationCount;
+#else
+  int handlerSwitchValue;
+  const unsigned char *actionRecord;
+  const unsigned char *languageSpecificData;
+  _Unwind_Ptr catchTemp;
+  void *adjustedPtr;
+#endif
+
+  _Unwind_Exception unwindHeader;
+};
+
 /* --------------------------------------------------------------
    -- The DB stuff below is there for debugging purposes only. --
    -------------------------------------------------------------- */
@@ -882,6 +912,22 @@
       || choice == (_Unwind_Ptr) &Foreign_Exception)
     return handler;
 
+  /* C++ exception occurrences.  */
+  if (propagated_exception->common.exception_class == CXX_EXCEPTION_CLASS
+      && Language_For (choice) == 'C')
+    {
+      void *choice_typeinfo = Foreign_Data_For (choice);
+      void *except_typeinfo =
+	(((struct __cxa_exception *)
+	  ((_Unwind_Exception *)propagated_exception + 1)) - 1)->exceptionType;
+
+      /* Typeinfo are directly compared, which might not be correct if they
+	 aren't merged.  ??? We should call the == operator if this module is
+	 compiled in C++.  */
+      if (choice_typeinfo == except_typeinfo)
+	return handler;
+    }
+
   return nothing;
 }
 
Index: sem_prag.adb
===================================================================
--- sem_prag.adb	(revision 203548)
+++ sem_prag.adb	(working copy)
@@ -7126,6 +7126,34 @@
                Check_CPP_Type_Has_No_Defaults (Def_Id);
             end if;
 
+         --  Import a CPP exception
+
+         elsif C = Convention_CPP
+           and then Ekind (Def_Id) = E_Exception
+         then
+            if No (Arg3) then
+               Error_Pragma_Arg
+                 ("'External_'Name arguments is required for 'Cpp exception",
+                  Arg3);
+            else
+               --  As only a string is allowed, Check_Arg_Is_External_Name
+               --  isn't called.
+               Check_Arg_Is_Static_Expression (Arg3, Standard_String);
+            end if;
+
+            if Present (Arg4) then
+               Error_Pragma_Arg
+                 ("Link_Name argument not allowed for imported Cpp exception",
+                  Arg4);
+            end if;
+
+            --  Do not call Set_Interface_Name as the name of the exception
+            --  shouldn't be modified (and in particular it shouldn't be
+            --  the External_Name). For exceptions, the External_Name is the
+            --  name of the RTTI structure.
+
+            --  ??? Emit an error if pragma Import/Export_Exception is present
+
          elsif Nkind (Parent (Def_Id)) = N_Incomplete_Type_Declaration then
             Check_No_Link_Name;
             Check_Arg_Count (3);


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