linux-kernel - Re: [PATCH 1/2] Correct function definition for C++

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Message-ID: <1487772051.5760.20.camel@infinera.com>
Date:   Wed, 22 Feb 2017 14:00:53 +0000
From:   Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
To:     "greg@...ah.com" <greg@...ah.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 1/2] Correct function definition for C++

On Wed, 2017-02-22 at 14:03 +0100, greg@...ah.com wrote:
> On Wed, Feb 22, 2017 at 07:50:46AM +0000, Joakim Tjernlund wrote:
> > On Wed, 2017-02-22 at 08:10 +0100, Greg KH wrote:
> > > On Tue, Feb 21, 2017 at 04:24:04PM +0100, Joakim Tjernlund wrote:
> > > > C++ does does not like the extra extern before asmlinkage, remove it.
> > > > 
> > > > Signed-off-by: Joakim Tjernlund <joakim.tjernlund@...inera.com>
> > > > ---
> > > >  include/linux/printk.h | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/include/linux/printk.h b/include/linux/printk.h
> > > > index 3472cc6..be823f5 100644
> > > > --- a/include/linux/printk.h
> > > > +++ b/include/linux/printk.h
> > > 
> > > 
> > > Why are you building this file with a C++ compiler?
> > 
> > virtualbox uses C++ and includes various kernel headers and the build
> > fails, virtualbox guest additions has not build for quite some time now and
> > this is one of the problems.
> 
> Virtualbox is a horrid pile of crap.  You can quote me on that.  We
> don't care about out-of-tree drivers, the authors should work to get
> them merged properly if they do care.

Sure, I believe you :)
 
But in this case it is not the kernel modules that fails, it is their
guest additions/xf86 video driver. Seem like that these need to include some
kernel herders there too.

> 
> Kernel code should be C, not C++, and if you do want to use C++, then
> you are on your own, sorry.

But there are already a lot of C++ adjustments!? Just grepping for __cplusplus shows
plenty of hits and what is the point of asmlinkage then:
#ifdef __cplusplus
#define CPP_ASMLINKAGE extern "C"
#else
#define CPP_ASMLINKAGE
#endif

#ifndef asmlinkage
#define asmlinkage CPP_ASMLINKAGE
#endif

I read all of this that C++ code should be able to at least include kernel headers
without fatal errors. 
You don't agree? In that case all __cplusplus/asmlinkage should be removed?

> 
> > > Also, this is not the correct way to submit patches for inclusion in the
> > > stable kernel tree.  Please read Documentation/stable_kernel_rules.txt
> > > for how to do this properly.
> > 
> > Sorry, I was in a hurry(lazy:) so I just included stable directly as
> > I know it needs to be fixed in 4.9 as well.
> 
> But that's not how to get a patch into the stable tree :(
> 
> sorry,

Right, my mistake. No need to be sorry, I got what I deserved :)

 Jocke

> 
> greg k-h