Re: LPC BoF - Linux Kernel Debugging & Drgn

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

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

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