4 ms·

> If your software runs always on the same platform then you can know what the behavior would be. This is not necessarily true, and I consider it to be a harmf

> If your software runs always on the same platform then you can know what the behavior would be. This is not necessarily true, and I consider it to be a harmful misconception. I think people under-react to "undefined behavior". What you think the platform would do if you overflowed an integer using machine instructions and what your C or C++ code ends up executing can be wildly different things because C and C++ compilers do everything in their power to optimize your code assuming your signed integers will never overflow. If they do, who knows what state your program is in or which machine instructions the compiler would have scheduled.

scoutt 6y ago
You are right. I might correct the sentence with "you can often know". Undefined behavior should be avoided but really is not that terrible.
- jjnoakes 6y ago
  We will have to agree to disagree. Fully understanding what a program might do if there is undefined behavior is not trivial. It requires basically reviewing and fully understanding the output assembler for every single build. Any change in system headers, compiler version, compiler flags, or source code might invalidate previous reviews. And programs with lurking undefined behavior may not seem dangerous but sufficiently clever exploits can do quite amazing things with the smallest of attack surfaces.
  - scoutt 6y ago
    Sure but in 17 years writing C for a living, with lines of code by the millions, and (embedded) devices running my code all over the world I still have to know about an integer overflow bug. Sure, I don't always write bug-free code (as anyone), but when I say it's not so terrible I mean that UD should be considered a rare case, and it's not worth even a single night of quiet sleep, let alone switching languages or overreacting. Hey, I am more afraid of a flipping bit due to power supply noises. And I don't want to say either that my code is perfect, or since it never happened to me it will never happen to you and that you can go around triggering UD everywhere since it's not a big deal. But I also like to warn young players that "boooo UD!" is just part of a FUD tactic for them to adopt some shiny new language.
    - pjmlp 6y ago
      Would you feel the same way when we finally manage to get liability laws for security exploits, like we are now discussing in Germany?
      - scoutt 6y ago
        If some of my systems fail, people might die. Should I still be worried for a liability?
        pjmlp 6y ago
        As an professional Engineer I would be.
    - jjnoakes 6y ago
      There is a ton of software out there that is riddled with bugs. Much of it is run behind closed doors, isn't exposed to attack vectors like the internet, and happily churns along because no one is trying to attack it. Lots of other software might be exposed to the internet or to malicious users but no one has stumbled across it and tried to exploit it yet. Code like that may be ok for now simply because of the circumstances, but I don't think that's a pass to ignore UB or to discourage folks from trying to improve the status quo. Because some day either the developer of that code, who is used to ignoring this kind of thing, might write some code that has to be more correct or it will get exploited. Or the code itself might get changed, or exposed to attackers, or copied into some other program. These things happen and they are preventable. And you don't even have to switch languages - turning on sanitizers when you compile and fixing issues as they are found, and encouraging others to do the same, is better (in my opinion) than categorizing folks worrying about and working on this issue - in C and in other languages - as FUD spreaders.
      - scoutt 6y ago
        There are worse things than can happen with bad wrote code other than security bugs. It doesn’t have to necessarily be exposed to the internet or users/attackers for bad things to happen. I truly believe that people just forgot this little fact. Again, I don’t discourage people from preventing UD, but, again, it’s not a big deal. Especially is not something to be afraid of. My code is as much as correct, verified, analyzed and tested as possible, and most of the times compliant with the most absurd certifications. Again, I still have to find a bug or fail a test because some strange UD.
asddubs 6y ago
yup, classic example: https://lwn.net/Articles/278137/ https://lwn.net/Articles/278137/

scoutt 6y ago

You are right. I might correct the sentence with "you can often know". Undefined behavior should be avoided but really is not that terrible.

jjnoakes 6y ago
We will have to agree to disagree. Fully understanding what a program might do if there is undefined behavior is not trivial. It requires basically reviewing and fully understanding the output assembler for every single build. Any change in system headers, compiler version, compiler flags, or source code might invalidate previous reviews. And programs with lurking undefined behavior may not seem dangerous but sufficiently clever exploits can do quite amazing things with the smallest of attack surfaces.
- scoutt 6y ago
  Sure but in 17 years writing C for a living, with lines of code by the millions, and (embedded) devices running my code all over the world I still have to know about an integer overflow bug. Sure, I don't always write bug-free code (as anyone), but when I say it's not so terrible I mean that UD should be considered a rare case, and it's not worth even a single night of quiet sleep, let alone switching languages or overreacting. Hey, I am more afraid of a flipping bit due to power supply noises. And I don't want to say either that my code is perfect, or since it never happened to me it will never happen to you and that you can go around triggering UD everywhere since it's not a big deal. But I also like to warn young players that "boooo UD!" is just part of a FUD tactic for them to adopt some shiny new language.
  - pjmlp 6y ago
    Would you feel the same way when we finally manage to get liability laws for security exploits, like we are now discussing in Germany?
    - scoutt 6y ago
      If some of my systems fail, people might die. Should I still be worried for a liability?
      - pjmlp 6y ago
        As an professional Engineer I would be.
  - jjnoakes 6y ago
    There is a ton of software out there that is riddled with bugs. Much of it is run behind closed doors, isn't exposed to attack vectors like the internet, and happily churns along because no one is trying to attack it. Lots of other software might be exposed to the internet or to malicious users but no one has stumbled across it and tried to exploit it yet. Code like that may be ok for now simply because of the circumstances, but I don't think that's a pass to ignore UB or to discourage folks from trying to improve the status quo. Because some day either the developer of that code, who is used to ignoring this kind of thing, might write some code that has to be more correct or it will get exploited. Or the code itself might get changed, or exposed to attackers, or copied into some other program. These things happen and they are preventable. And you don't even have to switch languages - turning on sanitizers when you compile and fixing issues as they are found, and encouraging others to do the same, is better (in my opinion) than categorizing folks worrying about and working on this issue - in C and in other languages - as FUD spreaders.
    - scoutt 6y ago
      There are worse things than can happen with bad wrote code other than security bugs. It doesn’t have to necessarily be exposed to the internet or users/attackers for bad things to happen. I truly believe that people just forgot this little fact. Again, I don’t discourage people from preventing UD, but, again, it’s not a big deal. Especially is not something to be afraid of. My code is as much as correct, verified, analyzed and tested as possible, and most of the times compliant with the most absurd certifications. Again, I still have to find a bug or fail a test because some strange UD.

asddubs 6y ago

yup, classic example: https://lwn.net/Articles/278137/ https://lwn.net/Articles/278137/