Re: [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel

[Joel Fernandes]

On Mon, Mar 11, 2019 at 6:28 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Mon, 11 Mar 2019 20:39:12 -0400
> Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote:
>
> > I think even though the kernel-headers can't have information about all data
> > structures, they do already contain a lot of data structure definitions we
> > need already. And anything needed can/should arguably be moved to include/ if
> > they are really needed for kernel extension by something "external" to the
> > kernel such as kernel modules or eBPF, right?
>
> That's not my worry. I would like to be able to easily walk data
> structures from within the kernel, without having to do a lot of work
> in userspace to get that information. The kprobe_events could then be
> passed type casts or such to access data fields of arguments to
> functions and such.

Ok.

> > In any case, such a solution such as what Steve suggested, still cannot do
> > what we can with headers - such as build kernel modules on the fly using the
> > C-compiler without any auto-generation of C code from any debug artifiacts.
> > Think systemtap working with the module-backend without any need for
> > linux-headers package on the file system. So such a solution would still be a
> > bit orthogonal in scope to what this proposed solution can solve IMO.
> >
>
> With the information I would like to have, it would be trivial to read
> the data to create the header files needed for modules.

But there are macros and other #define things too. We lose all of them
and can't recreate them from just DWARF (AFAIK). Including
include/generated/autoconf.h which #defines the CONFIG options. For
that we either need headers, or full kernel's sources with build
artifacts.

I do see a use case for the debug info you are talking about as you
mentioned for the kprobe_events argument list types, and I already
thought about it. But it does not seem to work for all the use cases I
am referring to here.

thanks,

 - Joel