Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
Date:   Sun, 24 Sep 2023 19:58:31 +0300
From:   Alexey Dobriyan <adobriyan@gmail.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org,
        linux-hardening@vger.kernel.org
Subject: Re: [GIT PULL] hardening fixes for v6.6-rc3
Message-ID: <88707e12-dba9-4a9f-95d7-8d6f3c8f0f58@p183>
References: <202309220957.927ADC0586@keescook>
 <CAHk-=wg0C+eEm0Tegpvc1zZjcqkdG9L0ed10tg_rQ1-WZciMGA@mail.gmail.com>
 <202309222034.F2B777F55@keescook>
 <CAHk-=whf6Zu3Cfm1eOTxXniZf5EPaf1iLj_q_6BVHrzTUBfUGw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAHk-=whf6Zu3Cfm1eOTxXniZf5EPaf1iLj_q_6BVHrzTUBfUGw@mail.gmail.com>
Precedence: bulk

On Sat, Sep 23, 2023 at 11:04:57AM -0700, Linus Torvalds wrote:
> On Fri, 22 Sept 2023 at 20:49, Kees Cook <keescook@chromium.org> wrote:
> >
> > 2) __cplusplus is relatively common in UAPI headers already:
> >    $ git grep __cplusplus -- include/uapi | wc -l
> >    58
> 
> Look a bit closer.
> 
> Most of those - by far - is for the usual
> 
>   #if defined(__cplusplus)
>   extern "C" {
>   #endif
> 
> pattern. IOW, it's explicitly not different code, but telling the C++
> compiler that "this is C code".
> 
> So this new #ifdef is an ugly new pattern of "do totally different
> things for C++".
> 
> Apparently required, but very ugly nonetheless.

Most of those in uapi/ are likely unnecessary: extern "C" means
"don't mangle", but kernel doesn't export functions to userspace
except vDSO so there is nothing to mangle in the first place.