Re: [RFA] Artifical dwarf2 debug info

[Andrew Cagney <ac131313 at redhat dot com>]

> That's right.
>
>
> > If that is the case then I don't think this is either necessary or 
> > correct.  A `struct frame_info' allows frame specific unwind functions - 
> > at present only dummy-frame and saved-regs-frame versions are 
> > implemented, however the next ones to implement are cfi-frame (unwind 
> > using CFI info) and regs-frame (unwind using the register cache).
> >
> > For your problem, wouldn't it be better to, instead of creating fake CFI 
> > info, implement custom frame unwind functions that handle your case?
>
> Hrm.  What do you mean by regs-frame?  If it's for the current frame
> wouldn't that be a frame which just doesn't unwind?
A frame that gets the saved registers from the register cache.  As for uses:
- an inner-most frame that for some reason doesn't unwind (i.e., 
create_new_frame() barfs).
- the frame that is inner to `current frame'.

> As for this situation, and the similar one for i386... there are three
> unwind functions, to find the previous frame's registers, ID, and PC.
> For this case we just want to express a normal function call which
> saves no registers; pretty easy.  But for i386 I'll want to express
> something which initially pushes a register, and then does some work,
> pops it, and does more work before returning.
So you're proposing that the saved-regs code be used to generate a cfi 
description as well?

Interesting.

Andrew


> There's plenty of ways to express that but it seems to me that the most
> useful one would be to have essentially a glorified prologue reader
> which builds that description.  Then the machinery to handle that
> description is - you guessed it - a standard CFI reader.  It might be
> nice to someday split up the CFI parser and executer so that we could
> provide the description less obtusely, but I'd hate to see us duplicate
> the machinery.


> BTW,
>     /* See description above.  The previous frame's resume address.
>        Save the previous PC in a local cache.  */
>     frame_pc_unwind_ftype *pc_unwind;
>
>     /* See description above.  The previous frame's resume address.
>        Save the previous PC in a local cache.  */
>     frame_id_unwind_ftype *id_unwind;
>
> Second comment is a past-o?
Thanks.

Andrew