linux-kernel - Re: [PATCH] sparse: use identifiers to define address spaces

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Message-ID: <20200618050249.lqwznznltm3lcykr@ltop.local>
Date:   Thu, 18 Jun 2020 07:02:49 +0200
From:   Luc Van Oostenryck <luc.vanoostenryck@...il.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sparse: use identifiers to define address spaces

On Thu, Jun 18, 2020 at 03:22:15AM +0200, Miguel Ojeda wrote:
> Hi Luc,

Hi Miguel,

> On Thu, Jun 18, 2020 at 12:02 AM Luc Van Oostenryck
> <luc.vanoostenryck@...il.com> wrote:
> >
> > diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> > index 21aed0981edf..e368384445b6 100644
> > --- a/include/linux/compiler_types.h
> > +++ b/include/linux/compiler_types.h
> > @@ -5,20 +5,20 @@
> >  #ifndef __ASSEMBLY__
> >
> >  #ifdef __CHECKER__
> > -# define __user                __attribute__((noderef, address_space(1)))
> >  # define __kernel      __attribute__((address_space(0)))
> > +# define __user                __attribute__((noderef, address_space(__user)))
> 
> I guess `__kernel` moves to the first place since it uses the first
> address space?

No, there is no really an order between address spaces. Even before
this patch, the number were only used as an ID to distinguish them
from each other.

I just moved __kernel above because it is quite different from
the others because it's the default one, and so:
* it's never displayed
* it's normally not needed, nor in type annotations, nor in cast
  between address spaces. The only time it's needed is when it's
  combined with a typeof to express "the same type as this one but
  without the address space"
* it can't be defined with a name, '0' must be used.

So, it seemed strange to me to have it in the middle of the other ones.

-- Luc