On Tue, Apr 09, 2019 at 04:00:34PM +0100, Qais Yousef wrote:
On 04/08/19 17:28, Joel Fernandes (Google) wrote:
Introduce in-kernel headers which are made available as an archive through proc (/proc/kheaders.tar.xz file). This archive makes it possible to run eBPF and other tracing programs tracing programs that need to extend the kernel for tracing purposes without any dependency on the file system having headers.
On Android and embedded systems, it is common to switch kernels but not have kernel headers available on the file system. 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 best way to use this feature is by building it in. Several users have a need for this, when they switch debug kernels, they donot want to update the filesystem or worry about it where to store the headers on it. However, the feature is also buildable as a module in case the user desires it not being part of the kernel image. This makes it possible to load and unload the headers from memory 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.
By having the archive available at a fixed location independent of filesystem dependencies and conventions, all debugging tools can directly refer to the fixed location for the archive, without concerning with where the headers on a typical filesystem which significantly simplifies tooling that needs kernel headers.
The code to read the headers is based on /proc/config.gz code and uses the same technique to embed the headers.
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
I applied both patches on 5.1-rc2 and managed to compile and run several eBPF programs using the untarred headers from /proc/kheaders.tar.xz on my juno.
Tested-by: Qais Yousef qais.yousef@arm.com
Thank you Qais! Masahiro, if Ok with you now could you give your tag?
thanks,
- Joel
v5 -> v6: (Masahiro Yamada suggestions mostly) - Dropped support for module building. - Rebuild archive if script changes. - Move archive file list to script. - Move build script to kernel directory. v4 -> v5: (v4 was Tested-by the following folks) Tested-by: qais.yousef@arm.com Tested-by: dietmar.eggemann@arm.com Tested-by: linux@manojrajarao.comThanks!
-- Qais Yousef