Re: How to get nice traceback with GNAT?

[Natasha Kerensikova <lithiumcat@instinctive.eu>]

On 2014-11-21, Randy Brukardt <randy@rrsoftware.com> wrote:
> "Natasha Kerensikova" <lithiumcat@instinctive.eu> wrote in message 
> news:slrnm6u97f.nrc.lithiumcat@nat.rebma.instinctive.eu...
>> Hello,
>>
>> I happen to have found a situation in which symbolic traceback is a
>> great help, but I have been a bit surprise by the (lack of) support in
>> the platform to which I have access.
>
> There is no standard for traceback, you are totally at the mercy of your 
> compiler vendor.

Indeed I am, but I don't think portability in debugging is that
important: I only need a set of tools that work on the platform where
debugging is performed. So when dealing with portable/fundamental bugs,
I'm free to choose the platform where the best tools for that task are
available.

>>In Debian/kFreeBSD, with GNAT 4.6, it looks like the following, which is
>>what I consider as perfect:
>>> 0x7fa993 in asis.ada_environments.open at asis-ada_environments.adb:241
>>> 0x481a57 in adactl at adactl.adb:90
>>> 0x417029 in main at b~adactl.adb:817
>>> 0x8015a4347 in ?? at ??:0
>>> 0x41706e in <_start> at ??:0
>
> No, perfect is:
> ** Unhandled CONSTRAINT_ERROR
>    Index or Subtype out of bounds - Pos of Error Value = -1
> On Line Number 484 In J2TYPE_PROFILE_CHECKING.END_SPEC_AND_DO_DELAYED_THUNKS
> Called from line number 1914 In J2SEMANTIC_ROUTINES.SEMANTICS
> Called from line number 466 In JANUS2.SEMDRIVER
> Called from line number 527 In JANUS2

It might be nitpicking, but as far as the traceback (word I
unfortunately missed in the subject) you actually provide less
information: GNAT has function name, file name, line number, while yours
lacks the file name (might be easy to find out, but that's still a
mental overhead nonetheless).

As far as the exception message goes, I agree that yours is quite
impressive. I didn't mention it in the OP because I'm actually chasing
user exceptions (explicit raise statements), so I have the power to
improve the exception message. Compare to the traceback, which is to
tied to the compiler internals that a mere user has no power to improve
anything. I can't even guess what is going in GNAT to get so wildly
different outputs on different platforms.



Natasha