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

[Daniel Jacobowitz]

On Thu, Apr 21, 2005 at 02:50:24PM -0400, Ron 603-884-2088 wrote:
> I propose the following replacement:
> 
>     A subroutine or entry point may also have a DW_AT_frame_base
>     attribute, whose value is a location description. Evaluation
>     of that location description computes the "frame base"
>     address, which can serve as a base pointer for accessing
>     locations in the frame of that subroutine or entry. In the
>     special case that the location expression is one of the
>     register name operators (see Section 2.5.1), the given
>     register is implicitly dereferenced to obtain the contents
>     of the register.

You're propogating the use of "dereference" to express what happens
here, and I don't think it's a good term.  Here's an example of why:

>     <i>For example, for the DW_AT_frame_base attribute (and
>     only that attribute) the location expression DW_OP_reg7
>     is equivalent to either of the expressions
>     <b>DW_OP_reg7 DW_OP_deref</b> or <b>DW_OP_breg7 0</b></i>.

I would interpret DW_OP_reg7 DW_OP_deref as "take the _contents_ of
reg7 and dereference that".  Or else just as nonsensical.

Basically, in the top level of a location description, DW_OP_reg7
refers to the location that is a register.  But inside expression
evaluation, the only meaningful interpretation is the contents of the
register.

-- 
Daniel Jacobowitz
CodeSourcery, LLC