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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Symbolic tracebacks on Debian
Date: Sun, 23 May 2010 16:52:32 +0100
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Date: 2010-05-23T16:52:32+01:00
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Stephen Leake <stephen_leake@stephe-leake.org> writes:

> Simon Wright <simon@pushface.org> writes:
>
>> "(see below)" <yaldnif.w@blueyonder.co.uk> writes:
>>
>>> On 21/05/2010 09:52, in article 82bpc8s17m.fsf@stephe-leake.org, "Stephen
>>> Leake" <stephen_leake@stephe-leake.org> wrote:
>>
>>>> Because symbolic traceback are not supported on _all_ gnat platforms, I
>>>> don't use them on _any_ - that way my code is portable. So I did not
>>>> notice this problem.
>>>> 
>>>> I dump the stack trace as hex addresses, then later run addr2line
>>>> manually if I want the symbolic trace.
>>>
>>> Can you say exactly what the steps are to do that?
>>> I've never understood it + therefore never used it.
>>
>> You need to call
>>
>>    GNAT.Exception_Traces.Trace_On
>>      (Kind => GNAT.Exception_Traces.Unhandled_Raise);
>
> I never do this.
>
>> from somewhere in your program and run gnatmake with -bargs -E.
>
> I only do this if I want symbolic traces from the running program, which
> I don't anymore.

If you want _symbolic_ traces you add

   GNAT.Exception_Traces.Set_Trace_Decorator
     (Decorator => GNAT.Traceback.Symbolic.Symbolic_Traceback'Access);

Actually, there is a difference: this code

   with GNAT.Exception_Traces;
   procedure T is
      Foo, Bar : exception;
      task T is
         entry Start;
      end T;
      task body T is
      begin
         accept Start;
         raise Bar;
      end T;
   begin
      GNAT.Exception_Traces.Trace_On
        (Kind => GNAT.Exception_Traces.Unhandled_Raise);
      T.Start;
      raise Foo;
   end T;

results in

   $ ./t

   Unhandled Exception raised
   Exception name: T.FOO
   Message: t.adb:16
   Call stack traceback locations:
   0x100001577 0x10000141b
   task t_0000000100800E00 terminated by unhandled exception
   Exception name: T.BAR
   Message: t.adb:10
   Call stack traceback locations:
   0x100001742 0x10000aa82 0x7fff825fb8b4

whereas with the Trace_On call commented out, it generates

   $ ./t

   Execution terminated by unhandled exception
   Exception name: T.FOO
   Message: t.adb:16
   Call stack traceback locations:
   0x10000157d 0x10000142b

so you get to see the unhandled exceptions in tasks too.