Re: LPC BoF - Linux Kernel Debugging & Drgn

[Stephen Brennan <stephen.s.brennan@oracle.com>]

And for anybody who didn't join, we had this guide as a way to get
started with drgn, using a locally built kernel in virtme-ng:

https://gist.github.com/brenns10/2064f16ea9b18235b47038d78775410d

Stephen Brennan <stephen.s.brennan@oracle.com> writes:
> Hi everyone,
>
> Thank you for joining the BoF, by all indication it was quite
> successful, despite my apparent attempts at sabotage by changing the
> room last minute. I took notes as we went (though couldn't cover
> everything), which I've included below.
>
> Thanks,
> Stephen
>
> ---
>
> ​* Drgn within IPython notebooks!  Useful to help people follow & understand debugging sessions. -Shung-Hsi Yu
>
> * What is the criteria for "contrib/" vs "helpers/"? - Sweet Tea Dorminy.
>   -> Unit test cases!
>   -> Converting contrib/ to helpers/ is a valid and good on-ramp to drgn development.
>   -> Though, not all contrib scripts are expected to make it in.
>   -> There is also a "tools/" directory which is actually tested & supported.
>
> * Is there a "rosetta stone" comparison between operations in drgn and crash?
>   -> Not currently!
>   -> I (Stephen) have some which I could move out of an internal wiki into Drgn's wiki.
>
> * Drgn "commands" vs Crash commands. Drgn does not yet have a command structure, it's been discussed.
>
> * What is the status of drgn without debuginfo? https://github.com/osandov/drgn/issues/176
>   -> Symbol tables implemented, kallsyms in review.
>   -> Minimal BTF implementation, has some issues.
>   -> CTF is used in production at Oracle.
>
> * What is the "backend" of drgn? How could you glue kgdb into Drgn?
>   -> The memory reader interface is the main way.
>   -> In addition to implementing memory readers, you'd need a way to communicate the "vmcoreinfo" to drgn. This provides info such as kernel version and kaslr offset.
>   -> We have a way to provide vmcoreinfo manually.
>   -> we're discussing gdbstub options: https://github.com/osandov/drgn/wiki/gdbstub-protocol-proposal:-linux.vmcoreinfo-query-packet
>
> * What's the minimum I need to do with root in drgn?
>   -> just opening /proc/kcore
>
> * Writing to kernel memory! New feature as of yesterday!
>   -> See https://blog.osandov.com/2024/09/17/calling-linux-kernel-functions-from-userspace.html
>
> Please join our Kernel Debuggers Matrix:
>     https://matrix.to/#/#linux-debuggers:matrix.org
> Please join our Kernel Debuggers Mailing List:
>     linux-debuggers@vger.kernel.org