[Bug debug/53927] wrong value for DW_AT_static_link

["ebotcazou at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53927

--- Comment #18 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> Jason suggested to change DW_AT_frame_base in order to make it equal to the
> address of the FRAME object. I was not sure:
> 
>  1) how to do it: location descriptions for all local variables would need
> to be updated;
>  2) whether it's safe to do this: what if optimizers move/duplicate this
> FRAME object in the stack frame or do similar "disturbing" things? I'm not
> familiar enough with optimization passes to estimate if it's likely:
> feedback welcome. :-)
> 
> I thought: why not make DW_AT_static_link compute the parent frame base
> address from the current static link argument? Well, when generating
> DW_AT_static_link for a nested subprogram, we do not know yet the offset
> between the FRAME object and the frame base address. This is because nested
> subprograms reach the back-end before their parent. Besides, see point 2:
> are we only sure that such a constant offset exists?

I think this is worth investigating though because it's conceptually much
simpler than adding yet another indirection.  And we should concentrate on -O0
(and -Og), we don't really care about what happens with aggressive
optimization.

I guess the question is: can we arrange to have a constant offset between the
frame base and the FRAME object, "constant" meaning valid for every function
but possibly target-dependent?