[Dwarf-discuss] Interpretation of FBREG: implied deref of frame_base?

[Ron 603-884-2088]

Jeff Nelson wrote:
>I'm a debugger developer on OpenVMS. One of the compilers I support is
>emitting a DW_AT_base_frame attribute that contains a single operator,
>DW_OP_regx. I believe this is incorrect, and that the compiler should
>emit a DW_OP_bregx instead. The difference is that the regx operator
>"names" the register whereas bregx resolves to the register value.

In discussing this issue with Jeff, I concluded that the
description of the DW_OP_fbreg operator and DW_AT_frame_base
are indeed a bit unclear.

However, consider the 5th example in Section 2.5.3/page 23 in V3),
which is identical to 5th example in Section 2.4.5/page 17 of V2).
I think that example only makes sense if the DW_AT_frame_base
attribute is interpreted to evalute to the frame pointer value
(rather than to the location that contains the frame pointer
value).

Which is to say, I think Jeff is correct in his interpretation.

Ron Brender