Re: new gdb arch routine FRAME_UNCHANGED

[Andrew Cagney <ac131313 at cygnus dot com>]

> On Fri, 10 May 2002 21:04:47 -0400, Andrew Cagney <ac131313@cygnus.com> said:
> 
> 
>   Andrew> Is the patch available somewhere?
> 
> Not online, but if you want me to, I'm happy to send the complete
> patch to gdb-patches so you can see where I'm going (or thought I was
> going... ;-).

Tossing out the work-in-progress will probably be useful - KevinB (ia64 
maintainer) would at very likely be interested in what is comming his 
way :-)  (I should also double check what HP's Assignement status is.)

>   Andrew> When you say unwind library support do you mean dwarf2cfi or
>   Andrew> something else?  From memory CFI identifies a frame using
>   Andrew> CFA and PC, I'm wondering how things work here.
> 
> The ia64 conventions come with their own unwind info.  The conventions
> do not define a unique address/identifier for each frame.

>   Andrew> cf:
>   Andrew> http://sources.redhat.com/ml/gdb-patches/2002-04/msg00749.html
>   Andrew> There is code through out GDB that relies on being able to
>   Andrew> re-find a frame in the frame chain.  The code typically
>   Andrew> relies on just the frame address (oops).  The referenced
>   Andrew> patch changes it to use frame/pc.  If I understand what
>   Andrew> you're saying correctly, still more information will need to
>   Andrew> be saved?
> 
> Yes, this is an issue I was wondering about, too.  My goal was fairly
> limited though: I just wanted to change gdb/ia64 to an unwind-info
> based implementation that works at least as well as the old version of
> gdb/ia64.  I didn't look into this specific issue.

> It sounds like for ia64 we would need to add a another field to struct
> frame_id to track the register stack address of a frame.  Otherwise, a
> recursive function that only uses the register stack would lead to a
> series of indistinguishable frames (a simple recursive factorial would
> do that).

Yep.

Hmm, is it possible to re-enter a function without changing the register 
stack pointer?  If it isn't then the register stack pointer could be 
used for frame->frame.

> Is the idea to treat frame_id as an opaque structure?  If so, I could
> add a routine to the unwind library API to obtain a unique frame-id
> for a given frame.  That way, the ia64 issue could be hidden behind
> the API.

The value can't be really opaque.  GUI code and MI are easier if they 
don't have to worry about malloc/free (frame_id being a lightweight) and 
MI needs to be able to pass the contents back to clients.

However, gdbarch methods to fill in and compare frame_id's could 
certainly be added.

Andrew