Re: [RFC] Replace regcache readonly flag with detached flag

[Yao Qi <qiyaoltc at gmail dot com>]

Alan Hayward <Alan.Hayward@arm.com> writes:

Hi Alan,

> In your regcache_1 constructor, you only NEW the cooked registers if the
> regcache is readonly.
> http://people.linaro.org/~yao.qi/gdb/doxy/regcache-split/gdb-xref/classregcache__1.html#acef3ef3bc85269cf04728901b4f28ee8
> In my version I only NEW the cooked registers in a detached register cache.

We can change regcache_1 constructor if it is wrong.  I am not saying my
patches are correct, let's commit them.  When I reviewed your patch, I
thought it is better to split regcache, then, I spent one day writing
the code to make sure the idea of splitting regcache makes sense.  I
post the doxygen link rather than patches, because my code is still
poor, but I think the doxygen is sufficient to show the design.

>
> As I understand it, the cooked registers exist because on some architectures
> extra state needs saving in the cooked registers (code comment: "some
> architectures
> need to save/restore `cooked registers that live in memory.”).
>
> Therefore the cooked register state needs to be a property of detached
> and not of
> readonly.
>

m_registers and m_register_status are fields of detached regcache, we
can definitely save cooked register state in detached regcache.

>
> A different issue is that we treat save/restore differently.
> In your code one of the recaches has to be both read-only (checking
> via gdb_assert) and detached.
> In my code the check is that the regcache is detached or
> not. Read-only is not relevant.

It is read-only in my code, but it doesn't have to be.  I don't see any
show-stoppers in the design of splitting regcache.  The attributes
"detached" and "read-only" are orthogonal in design.  Do you have some
comments on the overall design rather than the code details?  I'll
rewrite my patches, and post them.  It is unfortunate that it is hard to
review the overall design without the code.

-- 
Yao (齐尧)