From: Joel Fernandes <joel@joelfernandes.org>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
ast@kernel.org, atishp04@gmail.com, dancol@google.com,
Dan Williams <dan.j.williams@intel.com>,
gregkh@linuxfoundation.org, Guenter Roeck <groeck@chromium.org>,
Jonathan Corbet <corbet@lwn.net>,
karim.yaghmour@opersys.com, Kees Cook <keescook@chromium.org>,
kernel-team@android.com, linux-doc@vger.kernel.org,
linux-kselftest@vger.kernel.org,
linux-trace-devel@vger.kernel.org,
Manoj Rao <linux@manojrajarao.com>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
mhiramat@kernel.org, qais.yousef@arm.com, rdunlap@infradead.org,
rostedt@goodmis.org, Shuah Khan <shuah@kernel.org>,
yhs@fb.com
Subject: Re: [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel
Date: Tue, 5 Mar 2019 11:25:23 -0500 [thread overview]
Message-ID: <20190305162523.GA78911@google.com> (raw)
In-Reply-To: <934dc2dc-18b6-bc7c-9845-dac0577f7b47@arm.com>
On Mon, Mar 04, 2019 at 11:48:52PM +0100, Dietmar Eggemann wrote:
> On 3/1/19 5:08 PM, Joel Fernandes (Google) wrote:
> > Introduce in-kernel headers and other artifacts which are made available
> > as an archive through proc (/proc/kheaders.tar.xz file). This archive makes
> > it possible to build kernel modules, run eBPF programs, and other
> > tracing programs that need to extend the kernel for tracing purposes
> > without any dependency on the file system having headers and build
> > artifacts.
> >
> > On Android and embedded systems, it is common to switch kernels but not
> > have kernel headers available on the file system. Raw kernel headers
> > also cannot be copied into the filesystem like they can be on other
> > distros, due to licensing and other issues. There's no linux-headers
> > package on Android. Further once a different kernel is booted, any
> > headers stored on the file system will no longer be useful. By storing
> > the headers as a compressed archive within the kernel, we can avoid these
> > issues that have been a hindrance for a long time.
> >
> > The feature is also buildable as a module just in case the user desires
> > it not being part of the kernel image. This makes it possible to load
> > and unload the headers on demand. A tracing program, or a kernel module
> > builder can load the module, do its operations, and then unload the
> > module to save kernel memory. The total memory needed is 3.8MB.
> >
> > The code to read the headers is based on /proc/config.gz code and uses
> > the same technique to embed the headers.
> >
> > To build a module, the below steps have been tested on an x86 machine:
> > modprobe kheaders
> > rm -rf $HOME/headers
> > mkdir -p $HOME/headers
> > tar -xvf /proc/kheaders.tar.xz -C $HOME/headers >/dev/null
> > cd my-kernel-module
> > make -C $HOME/headers M=$(pwd) modules
> > rmmod kheaders
> >
> > Additional notes:
> > (1) external modules must be built on the same arch as the host that
> > built vmlinux. This can be done either in a qemu emulated chroot on the
> > target, or natively. This is due to host arch dependency of kernel
> > scripts.
> >
> > (2)
> > A limitation of module building with this is, since Module.symvers is
> > not available in the archive due to a cyclic dependency with building of
> > the archive into the kernel or module binaries, the modules built using
> > the archive will not contain symbol versioning (modversion). This is
> > usually not an issue since the idea of this patch is to build a kernel
> > module on the fly and load it into the same kernel. An appropriate
> > warning is already printed by the kernel to alert the user of modules
> > not having modversions when built using the archive. For building with
> > modversions, the user can use traditional header packages. For our
> > tracing usecases, we build modules on the fly with this so it is not a
> > concern.
> >
> > (3) I have left IKHD_ST and IKHD_ED markers as is to facilitate
> > future patches that would extract the headers from a kernel or module
> > image.
> >
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > ---
> >
> > Changes since v3:
> > - Blank tar was being generated because of a one line I
> > forgot to push. It is updated now.
> > - Added module.lds since arm64 needs it to build modules.
>
> Tested on x86 with eBPF scripts and exporting an alternative
> BCC_KERNEL_SOURCE.
>
> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Thank you! Will repost with the tags soon.
- Joel
next prev parent reply other threads:[~2019-03-05 16:25 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-01 16:08 [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel Joel Fernandes (Google)
2019-03-01 16:08 ` [PATCH v4 2/2] Add selftests for module build using in-kernel headers Joel Fernandes (Google)
2019-03-02 21:59 ` [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel kbuild test robot
2019-03-03 16:11 ` Joel Fernandes
2019-03-06 12:26 ` Masahiro Yamada
2019-03-06 17:49 ` Joel Fernandes
2019-03-07 4:59 ` Masahiro Yamada
2019-03-07 14:54 ` Joel Fernandes
2019-03-07 23:23 ` Justin Capella
2019-03-06 18:16 ` Joel Fernandes
2019-03-07 4:54 ` Masahiro Yamada
2019-03-03 2:04 ` kbuild test robot
2019-03-04 14:00 ` Qais Yousef
2019-03-05 16:27 ` Joel Fernandes
2019-03-04 22:48 ` Dietmar Eggemann
2019-03-05 16:25 ` Joel Fernandes [this message]
2019-03-07 8:58 ` Geert Uytterhoeven
2019-03-07 15:03 ` Joel Fernandes
2019-03-07 15:23 ` Greg KH
2019-03-07 16:54 ` Joel Fernandes
[not found] ` <20190318185742.109dee5c@alans-desktop>
2019-03-18 19:11 ` Daniel Colascione
2019-03-18 21:11 ` Karim Yaghmour
2019-03-08 8:53 ` Geert Uytterhoeven
2019-03-08 13:42 ` Joel Fernandes
2019-03-08 13:57 ` Enrico Weigelt, metux IT consult
2019-03-08 14:04 ` Greg KH
2019-03-08 14:02 ` Greg KH
2019-03-08 17:58 ` Joel Fernandes
2019-03-08 17:59 ` Geert Uytterhoeven
2019-03-09 7:16 ` Greg KH
2019-03-09 11:40 ` Geert Uytterhoeven
2019-03-09 12:11 ` Greg KH
2019-03-09 16:51 ` Karim Yaghmour
2019-03-09 19:26 ` Geert Uytterhoeven
2019-03-09 21:44 ` Karim Yaghmour
2019-03-11 8:03 ` Geert Uytterhoeven
2019-03-12 15:15 ` Karim Yaghmour
2019-03-11 23:36 ` Steven Rostedt
2019-03-11 23:58 ` Daniel Colascione
2019-03-12 0:39 ` Joel Fernandes
2019-03-12 1:28 ` Steven Rostedt
2019-03-12 1:38 ` Joel Fernandes
2019-03-13 1:18 ` Masami Hiramatsu
2019-03-14 12:27 ` Joel Fernandes
2019-03-15 13:14 ` Masami Hiramatsu
2019-03-12 1:45 ` Alexei Starovoitov
2019-03-12 15:26 ` Steven Rostedt
2019-03-12 1:22 ` Steven Rostedt
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