[Dwarf-discuss] PROPOSAL: Constant expressions in locations lists

[Cary Coutant]

> This was moved to the private mailing list and it doesn't look like  
> there
> has been any traffic about it for a while.  So I don't know what  
> its status is.
> I think the formulation should be adjusted a little from what was  
> proposed.
>
> The block is often overkill, but I think adding a plethora of
> constant_value[248] and so forth would be a waste of opcodes and  
> needless
> new repetition in decoding.  Instead, I suggest using a special suffix
> operation DW_OP_implicit_value.  It can follow DW_OP_const*,  
> DW_OP_lit*, etc.

My original proposal was (almost) exactly that, but several objected  
to that proposal on the basis that the DWARF expression stack is a  
simple stack of address-sized objects. Without a considerable  
overhaul of the DWARF expression language, it wouldn't be possible to  
describe constant values for anything other than integers no larger  
than a pointer. The new formulation sacrifices this ability to  
rematerialize a value for the ability to represent constant values of  
arbitrary type.

-cary