linux-kernel - Re: [PATCH] Compiler Attributes: move kernel-only attributes into __KERNEL_

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Date:   Wed, 28 Nov 2018 18:35:18 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     liuxiaozhou@...edance.com
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Paul Burton <paul.burton@...s.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] Compiler Attributes: move kernel-only attributes into __KERNEL__

Hi Xiaozhou,

On Wed, Nov 28, 2018 at 3:09 PM Xiaozhou Liu <liuxiaozhou@...edance.com> wrote:
>
> Attributes such as `__gnu_inline' are meant to be used within the
> kernel. When userspace somehow includes <linux/compiler.h>
> (eg. tools/bpf), compilation errors would be shown:
>
>         "error: unknown type name ‘__gnu_inline’"
>
> So just move these things into __KERNEL__ and the behavior is kept
> as before.

That is not exactly correct -- a3f8a30f3f00 moved some attributes to
another file, moving them into __KERNEL__ (in particular,__gnu_inline
is).

The problem is, instead, that __gnu_inline is not anymore defined
outside __KERNEL__, but something else that uses it is (the inline
macro definition, if I had to guess).

If your problem is fixed by putting __gnu_inline into __KERNEL__
again, it means we can simply move the inline definition inside
__KERNEL__ too. That way, we don't pollute userspace users with macro
definitions.

Having said that, does someone know whether userspace should have
access to those attributes (or rather, other code that uses in turn
those attributes)?

Cheers,
Miguel