From: Joel Fernandes <joel@joelfernandes.org>
To: Masahiro Yamada <yamada.masahiro@socionext.com>
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: Thu, 28 Feb 2019 18:27:51 -0500 [thread overview]
Message-ID: <20190228232751.GA218988@google.com> (raw)
In-Reply-To: <20190228144306.GA138215@google.com>
On Thu, Feb 28, 2019 at 09:43:06AM -0500, Joel Fernandes wrote:
> On Thu, Feb 28, 2019 at 11:17:51AM +0900, Masahiro Yamada wrote:
> > Hi Joel,
> >
> >
> > On Thu, Feb 28, 2019 at 4:40 AM Joel Fernandes (Google)
> > <joel@joelfernandes.org> 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.
> >
> >
> >
> > Please let me ask a question about the actual use-case.
> >
> >
> > To build embedded systems including Android,
> > I use an x86 build machine.
> >
> > In other words, I cross-compile vmlinux and in-tree modules.
> > So,
> >
> > target-arch: arm64
> > host-arch: x86
> >
> >
> >
> The other way we can make this work is using x86 usermode emulation inside a
> chroot on the Android device which will make the earlier commands work.
I verified the steps to build a module on my Pixel 3 (arm64) with Linux
kernel for arm64 compiled on my x86 host:
After building the headers, the steps were something like:
1.Build an x86 debian image with cross-gcc:
sudo qemu-debootstrap --arch amd64
--include=make,gcc,gcc-aarch64-linux-gnu,perl,libelf1,python
--variant=minbase $DIST $RUN_DIR http://ftp.us.debian.org/debian
2. Push qemu-x86_64-static (which I downloaded from the web) onto the device.
3. Tell binfmt_misc about qemu:
echo
':qemu-x86_64:M::\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x03\x00\x3e\x00:
\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/qemu-x86_64-static:OC'
> /proc/sys/fs/binfmt_misc/register
4. adb shell and then chroot into the image
5. follow all the steps in the commit message but set ARCH and CROSS_COMPILE
appropriately.
After Make, kernel module is cooked and ready :)
thanks,
- Joel
next prev parent reply other threads:[~2019-02-28 23:27 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-27 19:37 [PATCH v3 1/2] Provide in-kernel headers for making it easy to extend the kernel Joel Fernandes (Google)
2019-02-27 19:37 ` [PATCH v3 2/2] Add selftests for module build using in-kernel headers Joel Fernandes (Google)
2019-02-28 2:17 ` [PATCH v3 1/2] Provide in-kernel headers for making it easy to extend the kernel Masahiro Yamada
2019-02-28 14:43 ` Joel Fernandes
2019-02-28 23:27 ` Joel Fernandes [this message]
2019-03-01 6:25 ` Masahiro Yamada
2019-03-01 17:19 ` Joel Fernandes
2019-03-02 2:13 ` Masahiro Yamada
2019-03-02 2:39 ` Joel Fernandes
2019-03-04 5:40 ` Masahiro Yamada
2019-02-28 8:34 ` Masami Hiramatsu
2019-02-28 15:00 ` Joel Fernandes
2019-02-28 15:30 ` Greg KH
2019-02-28 15:37 ` Joel Fernandes
2019-02-28 15:45 ` Greg KH
2019-02-28 15:59 ` Joel Fernandes
2019-02-28 16:09 ` Steven Rostedt
2019-03-01 2:28 ` Masami Hiramatsu
2019-03-01 3:26 ` Joel Fernandes
2019-03-01 7:03 ` Masami Hiramatsu
2019-03-01 17:21 ` Joel Fernandes
2019-03-01 11:05 ` Qais Yousef
2019-02-28 13:53 ` Qais Yousef
2019-02-28 14:47 ` Joel Fernandes
2019-02-28 16:04 ` Dietmar Eggemann
2019-02-28 16:22 ` Qais Yousef
2019-02-28 16:48 ` Qais Yousef
2019-02-28 18:36 ` Dietmar Eggemann
2019-02-28 19:10 ` Joel Fernandes
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