Re: [PATCH v3 1/2] Provide in-kernel headers for making it easy to extend the kernel

From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexei Starovoitov <ast@kernel.org>,
	atish patra <atishp04@gmail.com>,
	Daniel Colascione <dancol@google.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Guenter Roeck <groeck@chromium.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Karim Yaghmour <karim.yaghmour@opersys.com>,
	Kees Cook <keescook@chromium.org>,
	kernel-team@android.com,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>,
	linux-trace-devel@vger.kernel.org,
	Manoj Rao <linux@manojrajarao.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	qais.yousef@arm.com, Randy Dunlap <rdunlap@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Shuah Khan <shuah@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>, Yonghong Song <yhs@fb.com>
Subject: Re: [PATCH v3 1/2] Provide in-kernel headers for making it easy to extend the kernel
Date: Mon, 4 Mar 2019 14:40:44 +0900	[thread overview]
Message-ID: <CAK7LNATjNE2g_HJnuqvTU7NuUeeUCa0Ogxf0Qru0yzkOT+n2-w@mail.gmail.com> (raw)
In-Reply-To: <20190302023940.GA55262@google.com>

> > > > Let me ask one more question.
> > > >
> > > > I guess this patch is motivated by
> > > > how difficult to convey kernel headers
> > > > from vendors to users.
> > > >
> > > > In that situation, how will the user find
> > > > the right compiler to use for building external modules?
> > > >
> > > >
> > > >
> > > >
> > > > Greg KH said:
> > > >
> > > > We don't ever support the system of loading a module built with anything
> > > > other than the _exact_ same compiler than the kernel was.
> > > >
> > > >
> > > > For the full context, see this:
> > > > https://lore.kernel.org/patchwork/patch/836247/#1031547
> > >
> > > IMO this issue is not related to this patch but is just an issue with
> > > building external modules in general.
> >
> >
> > I do not think it is an issue of the build system, at least.
> >
> > As far as I understood Greg's comment, it is troublesome
> > without the assumption that vmlinux and modules are built
> > by the same compiler.
> > It is related to this patch since this patch assumes use-cases
> > where external modules are built in a completely different environment,
> > where a different compiler is probably installed.
>
> Yes, but what I'm trying to say is the same issue exists with all other
> solutions today that do this. Such as debian you have linux-headers package.

Distributions provide the compiler in the standard path (/usr/bin/gcc),
and users are supposed to use it for building external modules.
That's the difference.

> A user could totally use the build artifacts obtained from somewhere to build
> a kernel module with a completely different compiler. That issue has just to
> do with the reality, and isn't an issue caused by any one solution such as
> this one.  I agree care must be taken whenever user is building external
> kernel modules independent of kernel sources.  Did I miss something else?
>
> thanks a lot,
>
>  - Joel
>

--
Best Regards
Masahiro Yamada