Why not initialize all variables to zero?

By: Gabriele Svelto (gabriele.svelto.delete@this.gmail.com), March 28, 2020 1:46 pm
Room: Moderated Discussions
Linus Torvalds (torvalds.delete@this.linux-foundation.org) on March 28, 2020 9:40 am wrote:
> The "but initializing will hide bugs" is one of those noises that people make without any real thought.
> It's become a mindless talking point, rather than a real argument. It's BS, in other words.

The fact that C allows access to an uninitalized variable is a flaw in the language that leads to real bugs. Automatically initializing variables to zero is no fix for that. It may be considered as a hardening measure - at least it doesn't allow nasty issues like user-after-free accesses within the stack - but it's no solution. And if you just do it blindly (à la Java) you're making very important tools like Valgrind completely useless and that will hide bugs for sure. Especially if you run automated test suites that include it. Or static analyzers for the matter.

> But those complex cases are also the ones that humans have most problems with, and that aren't
> really generally worth optimizing for, so zero-filling those cases automatically is probably a
> good idea, unless you have some odd code that doesn't care about security at all, and cares deeply
> about performance. And these days, that really should be seen as fairly unusual code.

Or you use a language that allows you to express - and check at compile time - that scenario so that the programmer can't get it wrong. Ever. Which means you don't pay the cost of initializing the buffer when it's not needed and you don't pay the cost of fixing the bug afterwards.

> In a perfect world, I think you'd have clearing by default, and then the option to manually override it for
> specific cases if you find that it's a performance problem and you can say "Yes, I pinky promise that I will
> initialize this myself" by annotating the declaration (or the allocation in case of malloc and friends).

Go have a look how Rust does it. You don't need a perfect world, just a modern language.
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TopicPosted ByDate
Why not initialize all variables to zero?Doug S2020/03/26 12:13 PM
  Most (all?) modern programming languages do this, right?Mark Roulo2020/03/26 04:44 PM
    Most (all?) modern programming languages do this, right?Konrad Scharz2020/03/27 01:09 AM
      Most (all?) modern programming languages do this, right?Gionatan Danti2020/03/27 03:13 AM
        Most (all?) modern programming languages do this, right?Foo_2020/03/27 03:45 AM
          Most (all?) modern programming languages do this, right?Gionatan Danti2020/03/27 09:19 AM
            Most (all?) modern programming languages do this, right?Foo_2020/03/28 02:32 AM
              Most (all?) modern programming languages do this, right?Montaray Jack2020/03/28 10:26 AM
      Most (all?) modern programming languages do this, right?Jeff S.2020/03/27 07:22 AM
        Most (all?) modern programming languages do this, right?anonymou52020/03/27 01:08 PM
  Why not initialize all variables to zero?Etienne2020/03/27 01:56 AM
    Why not initialize all variables to zero?NoSpammer2020/03/27 02:31 AM
  Why not initialize all variables to zero?Carlie Coats2020/03/27 06:17 AM
    Why not initialize all variables to zero?Jukka Larja2020/03/27 10:14 PM
      Why not initialize all variables to zero?Anon2020/03/28 12:01 AM
        Why not initialize all variables to zero?Jukka Larja2020/03/28 08:25 AM
          Why not initialize all variables to zero?Anon2020/03/28 11:20 AM
            Why not initialize all variables to zero?Jukka Larja2020/03/28 11:45 AM
              Why not initialize all variables to zero?Anon2020/03/28 01:21 PM
                Why not initialize all variables to zero?Jukka Larja2020/03/28 09:49 PM
    Why not initialize all variables to zero?Doug S2020/03/28 11:27 AM
      Why not initialize all variables to zero?Anon2020/03/28 01:24 PM
        Why not initialize all variables to zero?Carlie Coats2020/03/29 06:56 AM
  Why not initialize all variables to zero?Gabriele Svelto2020/03/27 06:52 AM
    Why not initialize all variables to zero?Foo_2020/03/28 02:34 AM
      Why not initialize all variables to zero?Linus Torvalds2020/03/28 09:40 AM
        Why not initialize all variables to zero?Doug S2020/03/28 11:21 AM
          Why not initialize all variables to zero?Linus Torvalds2020/03/28 01:01 PM
            Why not initialize all variables to zero?Etienne2020/04/02 01:14 AM
              Why not initialize all variables to zero?gallier22020/04/02 05:41 AM
              Why not initialize all variables to zero?Doug S2020/04/02 09:51 AM
        Why not initialize all variables to zero?Gabriele Svelto2020/03/28 01:46 PM
          Why not initialize all variables to zero?Linus Torvalds2020/03/28 04:28 PM
            Why not initialize all variables to zero?Anon32020/03/29 04:23 AM
            Why not initialize all variables to zero?Gabriele Svelto2020/03/29 12:28 PM
              Why not initialize all variables to zero?Anon32020/03/29 01:05 PM
                Why not initialize all variables to zero?Gabriele Svelto2020/03/30 12:52 AM
        Why not initialize all variables to zero?Carlie Coats2020/03/29 07:03 AM
        Why not initialize all variables to zero?gallier22020/03/29 11:48 PM
          Why not initialize all variables to zero?Michael S2020/03/30 02:24 AM
            Why not initialize all variables to zero?gallier22020/03/30 03:11 AM
        Why not discard variables after last use?2020/03/31 08:02 AM
          Makes no sense at allHeikki Kultala2020/03/31 01:01 PM
            An example (maybe)Mark Roulo2020/03/31 04:07 PM
              An example (maybe)Doug S2020/04/01 11:01 AM
                An example (maybe)Simon Farnsworth2020/04/02 02:21 AM
            Why not discard variables after last use?2020/04/02 12:41 PM
    Why not initialize all variables to zero?j2020/03/28 09:16 AM
    Why not initialize all variables to zero?Montaray Jack2020/03/28 11:42 AM
  Why not initialize all variables to zero?blaine2020/03/27 01:23 PM
    Why not initialize all variables to zero?James2020/03/28 03:18 AM
      Why not initialize all variables to zero?Anon32020/03/28 05:14 AM
      Why not initialize all variables to zero?Doug S2020/03/28 11:32 AM
        Why not initialize all variables to zero?Anon32020/03/28 11:45 AM
    Why not initialize all variables to zero?gallier22020/03/30 12:03 AM
  Why not initialize all variables to zero?gallier22020/03/29 11:32 PM
    Why not initialize all variables to zero?Michael S2020/03/30 02:30 AM
      Why not initialize all variables to zero?gallier22020/03/30 03:45 AM
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