On Sat, Apr 13, 2019 at 4:54 AM Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> 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. > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > --- I just noticed minor typos in comment lines (see below). Anyway, I have no more comment from the build system of view. So, Reviewed-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> > diff --git a/kernel/kheaders.c b/kernel/kheaders.c > new file mode 100644 > index 000000000000..19526294a4e8 > --- /dev/null > +++ b/kernel/kheaders.c > @@ -0,0 +1,74 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Provide kernel headers useful to build tracing programs > + * such as for running eBPF tracing tools. > + * > + * (Borrowed code from kernel/configs.c) > + */ > + > +#include <linux/kernel.h> > +#include <linux/module.h> > +#include <linux/proc_fs.h> > +#include <linux/init.h> > +#include <linux/uaccess.h> > + > +/* > + * Define kernel_headers_data and kernel_headers_data_end, within which the the > + * compressed kernel headers are stpred. The file is first compressed with xz. > + */ "the the" -> "the" ? "stpred" -> "stored" ? It is up to you if you want to send v8. -- Best Regards Masahiro Yamada
