Re: Gnat on OpenVMS

["Thierry Lelegard" <lelegard@club-internet.fr>]

Robert Dewar <robert_dewar@my-dejanews.com> a �crit dans le message :
> Very often, people like or dislike debuggers not based on the
> important part (the basic debugging engine), but rather on the
> look and feel of the user interface.

Well, at the present time, we only use the GDB command line
interface and we have no objection in using its syntax.

However, just allow me to think that crashing with "ACCVIO,
access violation" is an "unaesthetic" and "unfriendly" reply to
valid commands ;-)

> Actually most of the problems of GDB on VMS have been related
> to the debugging engine itself. VMS lacks the nice clean
> separation provided in Unix and NT systems between a debugger
> and its client, so basically GDB on VMS has to use a remote
> client server model.

VMS has its own definition of a debugger. The image activator
($IMGSTA phase) includes support for debugger activation. There
is a specific exception vector which is reserved for the debugger.
Most RTL's (such as ada and pthread RTL's) implement a standart
mechnisme called DBGEXT to interact with the debuggers.

These mechanisms are not exclusively used by VMSDEBUG. They
are also used by PCA, the performance analyzer.

I also used all these mechanisms to implement a "sort of"
debugger (actually, a spying tool for tracking random and
rare problems which appear only after a very long run in
an operational environment).

So, each OS defines its own concepts of a debugger. If a
debugger fits in this model, it can be very powerful. If
it refuses this model, it will always be inferior to native
debuggers.

GDB may be a good tool but it was design based on the UNIX
model of debugging. On VMS, GDB looks like me in an English
speaking environment: I understand most of what people say
but I remain a native French speaker and I do not always
understand fast speakers, specific or cultural jokes.
British and American people may like or hate me but,
for them, discussing with me will never be as easy as with
their fellow native English speakers.

Honestly, I hardly understand why it was so difficult to
integrate with the VMS debugger. The format of the debug tables
is public (appendix of the linker manual). All GNAT-specific
features could have been implemented by GNAT using a DBGEXT
entry in the GNAT RTL. The syntax of data is similar in Ada
83 and 95 and is already supported by the VMS debugger.
I agree that some OO features of Ada95 could be not very
well formatted (but GDB does not perform well either in
this area).

-Thierry
________________________________________________________
Thierry Lelegard, Paris, France
E-mail: lelegard@club-internet.fr