Re: frame->unwind->this_base()

[Daniel Jacobowitz <drow@mvista.com>]

On Tue, Mar 18, 2003 at 03:22:17PM -0500, Andrew Cagney wrote:
> >On Tue, Mar 18, 2003 at 12:28:47PM -0500, Andrew Cagney wrote:
> >
> >>>That would be a very bad assumption.  They are pratically guarenteed to 
> >
> >>>>be different.
> >
> >>>
> >>>
> >>>Then what do you mean by a "dwarf2 frame"?  I'd assume you meant the
> >>>CFA, but it sounds like you mean a frame for which we have dwarf2
> >>>.debug_info.
> >
> >>
> >>A frame with debug info provided by dwarf2.  CFI gives the register 
> >>info, location expressions give the variable info, ...
> >>
> >>What started out as a simple cfi-frame looks like it might need to 
> >>evolve into dwarf2-frame ...
> >
> >
> >DWARF-2 debug info does not corelate with CFI info.  For instance, GCC
> >will generate DWARF-2 CFI with stabs debug info.  It will also generate
> >CFI with no debug info at all, or DWARF-2 info without any CFI (if
> >requested).
> 
> True dwarf2 debug info or that .eh_frame stuff (i'm curious)?

Hmm, I thought it would write out .debug_frame without DWARF-2 but
peering at the GCC source I seem to be wrong again.  So just .eh_frame.

In any case, we'll parse both, so I stand by my statement.  We'll have
.eh_frame even without normal debug info.

> For stabs to work, it needs FRAME_LOCALS_ADDRESS(); and 
> FRAME_LOCALS_ADDRESS() relies on the prologue analyzer (since frame ID 
> won't correspond to `frame-base') for the computation of the correct 
> value; and that means unwinding the same frame two ways.  Outch.

Yeah...
 - if we have CFI use it to find the frame address.  Does this
become the frame ID?
 - if we have dwarf2 debug and CFI, then we don't need to do prologue
analysis; CFI should give us everything we need
 - if we have stabs debug and CFI, then we do need to do prologue
analysis to get FRAME_LOCALS_ADDRESS
 - if we have either kind of debug info and no CFI then we need to do
prologue analysis; for dwarf2 we'll also need to calculate the frame
base from DW_AT_frame_base in order to use it to find locals

Is that about right?

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer