[Dwarf-Discuss] Using DWARF for C++ runtime reflection

[Jason Nyberg]

Roman, For your given example:

  T   var1;
    DW_AT_name(T)   var2;

  typeid(var1)  ==  typeid (var2) ?

I think the type "T" found in the Dwarf info would have to have come from
the same compile unit that the "normally declared" type "T" came from, i.e.
your "DW_AT_name(...)" function would have to guarantee that. There's
nothing stopping the same type name from being used in different ways in
different source files, as long as they don't collide in the same compile
unit.

Your project sounds very interesting to me because I've *also* been using
Dwarf for reflection; in my case I combine (all in C) a minimalistic
language, Dwarf comprehension, and libffi such that shared libraries become
"native" extensions to my simple language just by importing them.
Eventually I'll hoist the whole thing up into C++ too...

On Tue, Mar 6, 2018 at 2:55 PM Michael Eager <eager at eagercon.com> wrote:

> >         Yes, assuming that the compiler generates a valid source type.
> >         In some
> >         cases, particularly with template classes, this may not be the
> case.
> >
> >
> >       So DWARF does not give any guarantees and it's up to compiler
> >     vendor to decide about DW_AT_name?
> >
> >
> > DWARF doesn't give guarantees, just suggestions. Practically speaking
> > there's certainly benefit to compilers ensuring they produce a
> > consistent name across different translation units - and potentially
> > even a consistent name across compilers (so that code built with
> > different compilers and then debugged can behave consistently/well). (or
> > consistent enough for a debugger to cope with it - but I think as Daniel
> > pointed out, having the debugger have to decompose the name and do
> > various type equivalences is painful - which might lean one towards
> > trying to produce more consistent names across GCC and Clang - the few
> > cases I know of (enums, for example) could probably be improved just for
> > the compiler self-consistency aspect and incidentally improve the cross
> > compiler consistency anyway)
>
> Exactly.  In many areas, the DWARF Standard is permissive.  There are
> specific constraints which are mentioned, but the producer is given a
> lot of latitude whether to generate complete or incomplete, good or poor
> DWARF.  DWARF guarantees the organization and structure of the data.
>
> There is a comment about names on the DWARF Wiki under Best Practices:
> http://wiki.dwarfstd.org/index.php?title=Best_Practices
>
>
> --
> Michael Eager    eager at eagercon.com
> 1960 Park Blvd., Palo Alto, CA 94306
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