Re: [RFC PATCH] Typed DWARF stack

[Tom Tromey <tromey@redhat.com>]

>>>>> "Jakub" == Jakub Jelinek <jakub@redhat.com> writes:

Jakub> This patch on top of
Jakub> http://gcc.gnu.org/ml/gcc-patches/2011-03/msg01224.html
Jakub> and
Jakub> http://gcc.gnu.org/ml/gcc-patches/2011-03/msg01723.html
Jakub> implements parts of Cary's typed DWARF stack proposal:
Jakub> http://www.dwarfstd.org/doc/040408.1.html

I've been implementing this in GDB and I have a couple of questions.

Should DW_OP_bra be restricted to integral types?  Several other opcodes
are restricted in this way, and it seems like an oversight to me that
DW_OP_bra is lacking this restriction.  (I've added this restriction in
GDB.)

Currently, the comparison operators are all defined as performing signed
operations.  So, what should happen in this case:

   DW_OP_lit0
   DW_OP_GNU_convert <unsigned int>
   DW_OP_GNU_const_type <unsigned int> -1
   DW_OP_gt

That is, should this ignore the type (perhaps just using the type
width), or is this a bug in the spec?

Either answer here has problems.

You can't really ignore the type, because that rules out floating point
comparisons.  I suppose you could special-case integral types.

However, since "ordinary" (that is, pre-typed-DWARF) DWARF values do not
have a consistent type, I think answering "bug" means having a special
case for such values -- because they are treated as unsigned in most
places, but signed in a few, and signed/unsigned type conversion should
presumably only be done for such "typeless" values, not all values.

I think I will implement the latter ("bug") approach.

Tom