Re: [PATCH v2 1/2] Provide in-kernel headers for making it easy to extend the kernel

From: Karim Yaghmour
Date: Wed Feb 13 2019 - 17:50:17 EST

On 2/11/19 9:35 AM, Joel Fernandes (Google) wrote:
Introduce in-kernel headers and other artifacts which are made available
as an archive through proc (/proc/kheaders.txz 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

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.txz -C $HOME/headers >/dev/null
cd my-kernel-module
make -C $HOME/headers M=$(pwd) modules
rmmod kheaders

Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>

Acked-by: Karim Yaghmour <karim.yaghmour@xxxxxxxxxxx>


Changes since v1:
- removed IKH_EXTRA variable, not needed (Masahiro Yamada)
- small fix ups to selftest
- added target to main Makefile etc
- added MODULE_LICENSE to test module
- made selftest more quiet

Changes since RFC:
Both changes bring size down to 3.8MB:
- use xz for compression
- strip comments except SPDX lines
- Call out the module name in Kconfig
- Also added selftests in second patch to ensure headers are always

Documentation/dontdiff | 1 +
init/Kconfig | 11 ++++++
kernel/.gitignore | 2 ++
kernel/Makefile | 27 ++++++++++++++
kernel/kheaders.c | 74 +++++++++++++++++++++++++++++++++++++++
scripts/ | 19 ++++++++++
scripts/ | 8 +++++
7 files changed, 142 insertions(+)
create mode 100644 kernel/kheaders.c
create mode 100755 scripts/
create mode 100755 scripts/


Karim Yaghmour
CEO - Opersys inc. /