Episode Details

Oxide and Friends Twitter Space: June 21, 2021

What’s a bug? What’s a debugger?

We’ve been holding a Twitter Space weekly on Mondays at 5p for about an hour. Even though it’s not (yet?) a feature of Twitter Spaces, we have been recording them all; here is the recording for our Twitter Space for June 21, 2021.

In addition to Bryan Cantrill and Adam Leventhal, speakers on June 21st included Dan Cross, Sean Klein, Aram Hăvărneanu, and the mononymous Nate. (Did we miss your name and/or get it wrong? Drop a PR!)

Some of the topics we hit on, in the order that we hit them:

• Adam’s toddler (being chased by a rooster) > Don’t get me wrong, some of my best friends are three-year-olds.
• [@3:12](https://youtu.be/UOucW3F7nCg?t=192) Sy Brand’s tutorial Writing a Debugger
  • Lobsters – when HN isn’t enough!
• [@4:34](https://youtu.be/UOucW3F7nCg?t=274) Bryan’s debuggers
  • MDB Modular Debugger > Adam: I think people are using cargo-cult debugging, rather than getting to the root cause > of these things, or being satisfied until they get to the root cause.
    > Bryan: I think with software systems, it’s really hard to know what they’re actually doing.
  • Procedure Linkage Table aka “the plits”
  • “Runtime Performance Analysis of the M-to-N Scheduling Model” (pdf) 1996 undergrad thesis (Brown CS dept website)

  • [@6:29](https://youtu.be/UOucW3F7nCg?t=389) Threadmon website and 1997 paper (a retooling of the ’96 paper) > When I built that tooling, it revealed this thing > is not doing at all what anyone thought it was doing.
  • TNF Trace Normal Form > Part of the problem with debuggers… debuggers are historically written by compiler folks, > and not system folks. As a result, debuggers are designed to debug the problem that > compiler folks have the most familiarity with, and that’s a compiler.
    > Debuggers are designed for reproducible problems, way too frequently.
• I view in situ breakpoint debugging as one sliver of debugging that’s useful for one particular and somewhat unusual class of bugs. That’s actually not the kind of debugger I want to use most of the time.
• Software breakpoints
• [@11:59](https://youtu.be/UOucW3F7nCg?t=719) > libdis was my intern project in 2000. The idea was to take the program text, > and interpret it in some structural form, and try to infer different things about the program.
  • Ghidra: software reverse engineering tool
  • Laura Abbott’s Exploiting Undocumented Hardware Blocks in the LPC55S69
  • Volatility: the memory forensics framework Adam couldn’t quite re