Btop Bug: Integer Underflow With The -u Flag

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Btop Bug: Integer Underflow with the -u Flag

Hey guys, let's dive into a weird little bug I found in btop, a cool resource monitor. I ran into an issue when playing around with the -u flag, and it seems like there's an integer underflow happening when you give it a number that's a bit too big. I'm going to walk you through what's up, how to make it happen, and what I think should be happening instead. I hope this helps the btop developers fix this. Also, it might help you to avoid this error when you are using btop in the future.

The Bug: Integer Underflow with the -u Flag in Btop

So, here's the deal: when you use the -u flag in btop and give it a really large number, things go sideways. Instead of, like, saying "Hey, that number's too big!" or clamping it down to a reasonable value, btop just uses it as is. This leads to an integer underflow, which is a fancy way of saying the number gets messed up because it's too big for the system to handle correctly. This can cause all sorts of unexpected behavior, which isn't good. Essentially, the program isn't properly checking the value and allowing an overflow or underflow to happen. I am sure that this kind of behavior is not what the developers intended and will be fixed soon.

I'm going to explain exactly how I found it, and what should be done. When you are using btop, you should be careful to avoid this bug. However, I am sure that the developers will fix it soon.

How to Make It Happen

Alright, so here's how you can see this bug for yourself. It's super easy to reproduce, which is good for the developers because it means they can quickly test and fix it. Basically, you just need to run btop with a specific command line option. Here's what you need to do to reproduce the integer underflow:

  1. Get Btop: Make sure you have btop installed on your system. You can either build it from source or download a pre-built version. If you build from source, follow the instructions in the README.md file. If you download a pre-built version, make sure it's the latest version available.
  2. Run with the -u Flag: Open your terminal and run btop with the -u flag. Give the flag a value that's a large number. Specifically, try 2147483648 or anything larger. The command should look something like this:
btop -u 2147483648

That's it! Now, the program should behave unexpectedly. The program should either reject the value or clamp it to the maximum allowable value.

What Should Happen Instead

So, what's the correct way for btop to handle this? Well, there are a couple of ways the developers could approach this issue, and either would be better than the current behavior. Here are a couple of approaches:

  1. Input Validation: The most straightforward solution is to add input validation. Before using the value provided with the -u flag, btop should check if it's within a valid range. If the value is too large or too small, it should either:
    • Clamp the Value: Set the value to the maximum or minimum acceptable value. This would ensure that btop still functions correctly without causing an integer underflow. For example, if the maximum allowed value is 2147483647, btop would just use that number instead. However, this is not a great solution because the users may not know that the value is changed. The users will be confused when the values are not matching what the users put in.
    • Error Out: Display an error message to the user and exit. This would inform the user that the input is invalid and prevent unexpected behavior. This is probably the best approach because it tells the user immediately that the value is wrong.
  2. Use a Different Data Type: If the -u flag represents a value that can potentially be very large, consider using a data type that can handle larger numbers. For example, you could use a long int or a similar data type that has a larger range. This would prevent integer overflow issues altogether. However, changing the data type could require changes throughout the code.

I think the best approach is to validate the input and show an error message. It's the most user-friendly way to handle invalid input and prevent unexpected behavior. The user will be notified immediately, and the issue will be fixed quickly.

Technical Details

  • Btop++ Version: I was using version 1.4.5. It's always a good idea to mention the version you are using when reporting a bug. This helps the developers reproduce the issue and understand the context.
  • Binary: I don't have this information. However, I can still report the bug. If you are having problems, then you should also include it in the report.
  • Architecture: I'm on an x86_64 system. This is a common architecture for most desktop computers.
  • Platform: I'm running Linux.
  • Kernel: I'm using kernel 6.17.7-arch1-1.
  • Terminal: I'm using kitty as my terminal emulator.
  • Font: I'm using JetBrainsMono NerdFontMono (14). This is just the font I use, but it's good to include it.

I hope that this information helps the developers and the users. It's important to provide as much detail as possible when reporting a bug, so the developers can fix it quickly.

Additional Context and Logs

When reporting a bug, it's really helpful to include any additional context that might be relevant. This can help the developers understand the issue and reproduce it. This includes the contents of ~/.local/state/btop.log. If that file is empty, try running btop with the --debug flag. This will provide more detailed logging information that can help diagnose the problem. The snap uses: ~/snap/btop/current/.local/state/btop.log.

GDB Backtrace

If btop is crashing when it starts, getting a GDB backtrace can be super helpful for debugging. Here's how to do it:

  1. Run with GDB: If you're on Linux, use gdb btop. On macOS, use lldb btop.
  2. Run the Program: Type r to run btop. Wait for it to crash, and press Enter if prompted.
  3. Get the Backtrace: In GDB, type thread apply all bt (or bt all on macOS) to get a backtrace for all threads. Copy and paste the backtrace in your bug report. This will give the developers a detailed view of what was happening when the crash occurred.

This kind of information is invaluable for pinpointing the source of the problem and getting it fixed quickly. I have not included it because btop does not crash when I run the command I showed. However, it's a good practice to include it if you are having issues.

Conclusion

So, there you have it, folks! A little integer underflow bug in btop that can be triggered by using a large number with the -u flag. It's not a major issue, but it's definitely something that should be addressed to prevent unexpected behavior. By following the steps I've outlined, you can easily reproduce this bug and help the developers fix it. Remember to always provide as much detail as possible when reporting a bug, and hopefully, this helps make btop even better! Thanks for reading and happy monitoring!