debuginfo: Find vmlinux at other locations

[Asphaltt]

On some distributions (e.g., Ubuntu), vmlinux may not reside in the modules directory. Search common locations for vmlinux, as referenced in: https://github.com/anakryiko/retsnoop/blob/389e2c9ddfc686ee048b063ce0c17b94b55398d2/src/retsnoop.c#L59-L67

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[brenns10]

Hi @Asphaltt, I'm actually gearing up to completely revamp this section of drgn-tools. Since drgn 0.0.31, drgn's Module API does a really great job of finding debug info -- and especially, allowing the user to customize the process. So in my development branch, we're dropping most of the code that searches the "standard directories" for debuginfo, and just relying on drgn to do that. We'll provide some extra logic for some things that may be a bit more specific to Oracle Linux, but lookups in the standard paths will use drgn's standard logic, and thus should work well on any distro without modification.

I'm also really curious, are there any specific helpers or tools you're using out of drgn-tools? I didn't know anybody outside Oracle was using it, and if there are rough edges I can help smooth out (including the debuginfo, which I'll do my best to get the changes out quickly), I would be glad to help.

[brenns10]

That said, the changes here look very reasonable, so I wouldn't have any problem including them before those changes I mentioned land.

[Asphaltt]

Thanks for these great drgn tools — honestly, they're the best alternatives to crash I've seen. Otherwise, I have to build some of these myself.

I'm actually gearing up to completely revamp this section of drgn-tools.

That’s great to hear. I'm looking forward to seeing the improvements!

Are there any specific helpers or tools you're using out of drgn-tools?

Not yet. When I first explored these tools on Ubuntu, I ran into an issue:

$ sudo corelens /proc/kcore -M sys
warning: Running corelens against a live system.
         Data may be inconsistent, or corelens may crash.
error: could not find debuginfo (tried DWARF)

I had to fix that first before I could start using them properly.

And with that, here’s the PR.

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[brenns10]

With pre-commit fixes, this looks good to me.

[brenns10]

Thank you! If you'd like, I can mention you on the PR for the broader changes to debuginfo loading, so you can have a look yourself.

[Asphaltt]

If you'd like, I can mention you on the PR for the broader changes to debuginfo loading, so you can have a look yourself.

Seems cool. Thank you!