Re: [rfc] Unwind the ARM CPSR

[Joel Brobecker <brobecker@adacore.com>]

> So why shouldn't the argument be the CURRENT (i.e. THIS) frame
> instead?  Then we can call frame_register (CURRENT) instead of
> frame_unwind_register (NEXT) to get the same result, plus we'll
> have the option of calling frame_unwind_register (CURRENT) when
> we need it.

I can see why you'd like some feedback. This (amazing piece of) code
has always been a bit difficult for me to grasp in its entirety...
I hope others will take some time to think about it too, because
I don't feel sufficiently proficient to provide a confident answer.

FWIW, I don't see how we could end up breaking something with your
approach. As it turns out, there is a comment that says about
the prev_register method:

   Why not pass in THIS_FRAME?  By passing in NEXT frame and THIS
   cache, the supplied parameters are consistent with the sibling
   function THIS_ID.

So it sounds like the author wasn't seeing any issue with that
either.

I personally think that passing the current frame will make
this function a little easier to understand too, no? (I find
the twist of computing the caller's registers of this frame
using the next frame a constant mental exercise)

> Of course this would be a pain to change all at once since there are
> so many unwinders.  I'd introduce a new method instead
> (unwind->prev_register_this?).  What do you think?

Sounds like a possible plan to me.

-- 
Joel