Re: [PATCH] Don't attach to 'target_changed' observer in regcache

[Mark Kettenis <mark dot kettenis at xs4all dot nl>]

> From: Yao Qi <yao@codesourcery.com>
> Date: Thu, 2 Aug 2012 15:17:27 +0800
> 
> Hi,
> When I am modifying 'target_changed' observer, I don't understand
> why we attach regcache_observer_target_changed to 'target_changed'
> observer, and invalidates all regcache.  'target_changed' observer
> is notified in valops.c:value_assign, before that, register is
> modified by calling either gdbarch_value_to_register or
> put_frame_register_bytes.  Looks like regcache is in a good state,
> why do we have to invalidate them?
> 
> The code that invalidates all regcache was added by this patch,
> 
>   Multiplexed registers and invalidating the register cache
>   http://sourceware.org/ml/gdb-patches/2004-04/msg00282.html
> 
> The author (Orjan) tried to support "changing the bank select register
> changes the contents (and meaning) for a whole set of other registers."
> The requirement is quite specific to Orjan's own port, so the better
> solution is to attach a function which invalidates all regcache in
> Orjan's backend, instead of doing it in target-independent part.

Banked registers aren't really that exotic.  Especially if you realise
that register windows (SPARC, IA-64) are essentially banked registers.

I fear you're trading speed for correctness here.
> 
> 2012-08-02  Yao Qi  <yao@codesourcery.com>
> 
> 	* regcache.c (regcache_observer_target_changed): Remove.
> 	(_initialize_regcache): Don't call observer_attach_target_changed.