Re: Variable values before initialisaton

["Rob Quill" <rob.quill@gmail.com>]

On 27/11/06, Jim Blandy <jimb@codesourcery.com> wrote:
>
> Daniel Jacobowitz <drow@false.org> writes:
> > On Fri, Nov 24, 2006 at 09:52:52AM +0300, Vladimir Prus wrote:
> >> Can you clarify? Certainly, each constructor invocation produces a finite
> >> number of processor instruction. You can identify the "last" instruction of
> >> those, and hack gcc to produce file last_instructions_of_ctors.txt and make
> >> gdb read such file and do the right thing.
> >
> > You can have:
> >
> >   - Initialize part A of structure
> >   - Read part A of structure
> >   - Initialize rest of structure
> >
> > You don't want GDB to be unable to display the structure at that read,
> > do you?  So you need to know which bits of it are initialized and which
> > aren't.  And, in some cases, you want to be able to debug a structure
> > pointer after "new" returns some storage but before the constructor is
> > invoked.
> >
> > I suppose this is doable though: a very interesting project for someone
> > interested in learning about debug info formats and generation would be
> > to annotate initializedness somehow.  The compiler does know.  But it
> > wouldn't be easy.
>
> I think this is a bit afield from Rob's original question.  In the
> code he posted:
>
>     int i = 0;
>     int j = 2;
>     int k = 3;
>
> the issue isn't initialization.  Rather it's that the scope of k
> doesn't include the declarations of i and j, but GCC collapses all
> these declarations into one block, so GDB thinks k's scope does
> include the first two lines.  If GCC produced DW_AT_start_scope
> attributes (p. 61, #11 in DWARF 3), and GDB understood them, then this
> would work.
>

Interesting. Is it that GCC doesn't implement it, or that GDB doesn't
understand it, or both? How difficult to you think it would be to
implement, because I think it would be quite good to have it right.

Thanks,
Rob