[RFA/RFC] New command: ``start''
Joel Brobecker
brobecker@gnat.com
Tue May 18 22:27:00 GMT 2004
> > As briefly discussed on gdb@ and gdb-patches@, here is a first proposal
> > for the addition of a new command: ``start''.
> >
> > I handled the language-dependent issue by adding a new method to the
> > language vector. I returns a newly allocated string that tells GDB
> > where to insert the breakpoint. I named it "main_program_name" because
> > I would expect it to always return the name of a procedure. However,
> > it can actually return any location expression. So a language could
> > use a different approach and return something like "*0xdeadbeef" or
> > "source.c:10" for instance.
>
> We already have a function for this: main_name. Is it adequate for
> Ada?
I forgot about this function. But I don't think it's adequate for the
start command. If I understand everything correctly, this function
relies on some information provided in stabs via N_MAIN symbols.
Otherwise, it defaults to "main". This wouldn't necessarily work
with any debug format.
Also, the purpose of this function is slightly different from what
I am trying to achieve with the language method: Despite the fact that
most users see Ada programs starting at the begining of their main
procedure, a closer approximation is that it starts inside procedure
main() too.
To give you a better understanding how who it works in Ada (as defined
in the Reference Manual [RM for short]), the execution of an Ada program
has 3 important phases: 1. Elaboration
2. Program execution
3. Finalization
The RM says that the elaboration should be performed inside a procedure
called "adainit", and that the finalization should be performed by a
procedure called "adafinal". The elaboration and finalization order
is computed by a tool called the "binder" that checks all the
dependencies, and generate a small source file that looks like this:
void
adainit (void)
{
/* Do the program elaboration here. */
}
void
adafinal (void)
{
/* Finalize the program. */
}
void
int
main (...)
{
adainit ();
the_user_main_program ();
adafinal ();
}
The last step when building a program is then to call the gnat linker
that will do 2 things: compile the file generated by the binder,
and then do the link. (this is all automated by our gnatmake tool :).
So, even though most Ada users will usually only care about their
own main procedure, I occasionally need to go up the stack up
to procedure "main" to inspect it.
Adapting main_name() to fit the purpose of the start command would
cause the backtrace (amount other things) to be a bit shorter, and
also depend on the current language.
One thing that might be worthwhile, though, is call it from
xdefault_main_program_name, instead of hard-coding "main" a second time.
But that might introduce an unwanted dependency.
--
Joel
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