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pcwalton's profile
Patrick Walton
Patrick Walton
Patrick Walton
@pcwalton

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Patrick Walton

@pcwalton

Research engineer at Mozilla

San Francisco, CA
pcwalton.github.io
Joined November 2009

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    1. John Regehr‏ @johnregehr 23 Sep 2019
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      John Regehr Retweeted Shafik Yaghmour

      ideally there's a two step process here: 1. make a sanitizer for the UB available 2. later on, exploit the UB for optimization we're doing these things backwards way too oftenhttps://twitter.com/shafikyaghmour/status/1176243229047451648 …

      John Regehr added,

      Shafik Yaghmour @shafikyaghmour
      LLVM removing stores to constant memory (which is undefined behavior): http://releases.llvm.org/9.0.0/docs/ReleaseNotes.html#noteworthy-optimizations … catches real bug: https://bugs.llvm.org/show_bug.cgi?id=42763 … #programming pic.twitter.com/9tI6lUoSaP
      Show this thread
      13 replies 36 retweets 150 likes
      Show this thread
    2. Filip Jerzy Pizło‏ @filpizlo 23 Sep 2019
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      Replying to @johnregehr

      Or zero steps: don’t do optimizations that break existing code.

      2 replies 0 retweets 1 like
    3. John Regehr‏ @johnregehr 23 Sep 2019
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      Replying to @filpizlo

      you know as well as I do that existing C/C++ code does everything, so clearly one has to make some hard choices here

      4 replies 0 retweets 7 likes
    4. Filip Jerzy Pizło‏ @filpizlo 24 Sep 2019
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      Replying to @johnregehr

      Existing JS code does everything too and yet that committee is able to keep 99% (probably more nines than that) working despite the language growing significantly.

      1 reply 0 retweets 0 likes
    5. Filip Jerzy Pizło‏ @filpizlo 24 Sep 2019
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      Replying to @filpizlo @johnregehr

      And not sure that PDP11 has anything to do with it. That’s the opposite argument, that says we should make the spec flexible for implementors. Implementors have already settled ABI disputes that prevented the spec from being more specific in the past so that’s not a valid excuse.

      1 reply 0 retweets 0 likes
    6. John Regehr‏ @johnregehr 24 Sep 2019
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      Replying to @filpizlo

      the point is that "don't break any programs" is a nonsensical position when we're talking about C and C++. a lot of old (and even new) codes work only because use after free behaves a certain way, and you're going to keep supporting those? I doubt it

      4 replies 0 retweets 1 like
    7. Gok‏ @Gok 24 Sep 2019
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      Replying to @johnregehr @filpizlo

      Agreed; that ship sailed the moment people decided that strict aliasing was a workable idea

      2 replies 0 retweets 0 likes
    8. Patrick Walton‏ @pcwalton 24 Sep 2019
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      Replying to @Gok @johnregehr @filpizlo

      Heck, I’m pretty sure there are some programs out there using inline asm that depend on the specific register allocation that some compiler came up with.

      1 reply 0 retweets 2 likes
      Patrick Walton‏ @pcwalton 24 Sep 2019
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      Replying to @pcwalton @Gok and

      Older versions of the GCC inline asm docs allude to programs doing this.pic.twitter.com/RRGPSGOR5f

      10:44 AM - 24 Sep 2019
      • 4 Likes
      • Brian who survived a powerline Jed Davis 🏳️‍🌈 whitequark John Regehr
      2 replies 0 retweets 4 likes
        1. John Regehr‏ @johnregehr 24 Sep 2019
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          Replying to @pcwalton @Gok @filpizlo

          nice, ouch

          0 replies 0 retweets 1 like
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        1. Filip Jerzy Pizło‏ @filpizlo 25 Sep 2019
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          Replying to @pcwalton @Gok @johnregehr

          This is another silly argument. It’s not hard to see that there is a difference between a program relying on something like register allocation inside an inline asm and a program relying on the fact that const never meant anything. You’re smart enough to see that difference.

          0 replies 0 retweets 0 likes
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