linux-kernel - Re: [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel

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Message-Id: <20190313101843.800dd8d6a9babb635580ebdc@kernel.org>
Date:   Wed, 13 Mar 2019 10:18:43 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Daniel Colascione <dancol@...gle.com>,
        Karim Yaghmour <karim.yaghmour@...rsys.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexei Starovoitov <ast@...nel.org>,
        atish patra <atishp04@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Guenter Roeck <groeck@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        linux-trace-devel@...r.kernel.org,
        Manoj Rao <linux@...ojrajarao.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Qais Yousef <qais.yousef@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Shuah Khan <shuah@...nel.org>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH v4 1/2] Provide in-kernel headers for making it easy to
 extend the kernel

On Mon, 11 Mar 2019 18:38:49 -0700
Joel Fernandes <joelaf@...gle.com> wrote:

> On Mon, Mar 11, 2019 at 6:28 PM Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > On Mon, 11 Mar 2019 20:39:12 -0400
> > Joel Fernandes <joel@...lfernandes.org> wrote:
> >
> > > I think even though the kernel-headers can't have information about all data
> > > structures, they do already contain a lot of data structure definitions we
> > > need already. And anything needed can/should arguably be moved to include/ if
> > > they are really needed for kernel extension by something "external" to the
> > > kernel such as kernel modules or eBPF, right?
> >
> > That's not my worry. I would like to be able to easily walk data
> > structures from within the kernel, without having to do a lot of work
> > in userspace to get that information. The kprobe_events could then be
> > passed type casts or such to access data fields of arguments to
> > functions and such.
> 
> Ok.
> 
> > > In any case, such a solution such as what Steve suggested, still cannot do
> > > what we can with headers - such as build kernel modules on the fly using the
> > > C-compiler without any auto-generation of C code from any debug artifiacts.
> > > Think systemtap working with the module-backend without any need for
> > > linux-headers package on the file system. So such a solution would still be a
> > > bit orthogonal in scope to what this proposed solution can solve IMO.
> > >
> >
> > With the information I would like to have, it would be trivial to read
> > the data to create the header files needed for modules.
> 
> But there are macros and other #define things too. We lose all of them
> and can't recreate them from just DWARF (AFAIK). Including
> include/generated/autoconf.h which #defines the CONFIG options. For
> that we either need headers, or full kernel's sources with build
> artifacts.

What kind of macros would you concern?

> I do see a use case for the debug info you are talking about as you
> mentioned for the kprobe_events argument list types, and I already
> thought about it. But it does not seem to work for all the use cases I
> am referring to here.

But the eBPF is based on kprobe-events. What kind of usage would you
expected? (with macros??)

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>