think-o: dwarf2 CFA != frame->frame (x86-64)

[Andrew Cagney]

> On Tue, 9 Apr 2002, Andrew Cagney wrote:
> 
> 
>> > 
>> > It might just be misnamed.
> 
>> 
>> No.  DW_OP_fbreg refers explicitly to DW_AT_frame_base.  CFA is a 
>> concept local to the CFI.  They would typically evaluate to the same 
>> value though.
> 
> DW_AT_frame_base is part of the .debug_info section.
> This is symbolic debug info, none of which is required to be present in an 
> executable
> On the other hand, the CFA info is required to be present on x86-64, 
> specifically for the purposes of unwinding the stack.

And?

> So you can't say that it should use DW_AT_frame_base. It can't.
> DW_AT_frame_base is a completely different concept. It is not intended to 
> have anything to do with unwinding the stack.  It also has nothing 
> necessarily to do with a real frame base. See 3.3.5.  This is why it's in 
> quotes.  Most compiler use it in way 1 described in that section, to 
> simplify location descriptions. 

(Didn't I point you at 3.3.5? :-).

Location expressions use DW_OP_fbreg when they need to refer to the 
stack.  DW_OP_fpreg is defined in terms of DW_AT_frame_base.  Can you 
please point me to the section where a location expression OP directly 
(not indirectly as in a register) refers to the CFA?

> For all intents and purposes, the CFA is the frame base when using dwarf2 
> cfi info.

If you read my original e-mail, you'll notice that I observed that the 
two most likely end up having the same value.

Andrew