On Fri, Apr 26, 2019 at 03:04:29PM -0400, 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 that need to extend the > kernel for tracing purposes without any dependency on the file system > having headers. > > A github PR is sent for the corresponding BCC patch at: > https://github.com/iovisor/bcc/pull/2312 > > 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. This is an issue even well known to distros. > 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 do not 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 can > load the module, do its operations, and then unload the module to save > kernel memory. The total memory needed is 3.3MB. > > 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. > > Other approaches were discussed such as having an in-memory mountable > filesystem, but that has drawbacks such as requiring an in-kernel xz > decompressor which we don't have today, and requiring usage of 42 MB of > kernel memory to host the decompressed headers at anytime. Also this > approach is simpler than such approaches. > > Reviewed-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
