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  3. I guess people are just going to keep discovering that you can't really make a C compiler do constant time

I guess people are just going to keep discovering that you can't really make a C compiler do constant time

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  • John RegehrR John Regehr

    "Can it be fair to require the average programmer to understand inline assembly, or any of these other inherently obtuse obfuscation techniques?"

    can it be fair for the average programmer (if they don't understand this stuff) to just not write code where timing channels matter? who even writes these articles

    SiguzaS This user is from outside of this forum
    SiguzaS This user is from outside of this forum
    Siguza
    wrote last edited by
    #14

    @regehr even the best programmers in the world struggle with this kind of stuff, ffs...

    1 Reply Last reply
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    • Per VognsenP This user is from outside of this forum
      Per VognsenP This user is from outside of this forum
      Per Vognsen
      wrote last edited by
      #15

      @rygorous @regehr Petition to rename to -fun-math.

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      • Per VognsenP This user is from outside of this forum
        Per VognsenP This user is from outside of this forum
        Per Vognsen
        wrote last edited by
        #16

        @rygorous @regehr -fhonor-yahweh -fhonor-buddha -fhonor-brahma just to be safe. You need all the help you can get with -ffast-math.

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        • John RegehrR This user is from outside of this forum
          John RegehrR This user is from outside of this forum
          John Regehr
          wrote last edited by
          #17

          @rygorous

          well, if the problems are important enough, something like this:

          https://discourse.llvm.org/t/rfc-constant-time-coding-support/87781

          1 Reply Last reply
          0
          • John RegehrR John Regehr

            I guess people are just going to keep discovering that you can't really make a C compiler do constant time

            https://www.theregister.com/2026/02/09/compilers_undermine_encryption/

            kaoudisK This user is from outside of this forum
            kaoudisK This user is from outside of this forum
            kaoudis
            wrote last edited by
            #18

            @regehr all I will say to that is eyup

            John RegehrR 1 Reply Last reply
            0
            • John RegehrR This user is from outside of this forum
              John RegehrR This user is from outside of this forum
              John Regehr
              wrote last edited by
              #19

              @rygorous @pervognsen aw, look at all the little nans and infs flying and being free!!!

              Per VognsenP 1 Reply Last reply
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              • kaoudisK kaoudis

                @regehr all I will say to that is eyup

                John RegehrR This user is from outside of this forum
                John RegehrR This user is from outside of this forum
                John Regehr
                wrote last edited by
                #20

                @kaoudis I've not been paying too much attention to the LLVM effort-- anything interesting going on there? or should I just dig into the discourse?

                kaoudisK 1 Reply Last reply
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                • John RegehrR John Regehr

                  @rygorous @pervognsen aw, look at all the little nans and infs flying and being free!!!

                  Per VognsenP This user is from outside of this forum
                  Per VognsenP This user is from outside of this forum
                  Per Vognsen
                  wrote last edited by
                  #21

                  @regehr @rygorous My first thought was, if this is meant for the far future, assuming they retain our current warning symbol for radiation seems a bit hopeful.

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                  • John RegehrR John Regehr

                    @kaoudis I've not been paying too much attention to the LLVM effort-- anything interesting going on there? or should I just dig into the discourse?

                    kaoudisK This user is from outside of this forum
                    kaoudisK This user is from outside of this forum
                    kaoudis
                    wrote last edited by
                    #22

                    @regehr I think* @wizardengineer landed the first bits of that work!

                    *I left trail of bits voluntarily (and for reasons unrelated) a bit before this happened though

                    John RegehrR 1 Reply Last reply
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                    • Janne MorenJ This user is from outside of this forum
                      Janne MorenJ This user is from outside of this forum
                      Janne Moren
                      wrote last edited by
                      #23

                      @rygorous @regehr
                      Rename to -ffast-bad-math perhaps?

                      1 Reply Last reply
                      0
                      • kaoudisK kaoudis

                        @regehr I think* @wizardengineer landed the first bits of that work!

                        *I left trail of bits voluntarily (and for reasons unrelated) a bit before this happened though

                        John RegehrR This user is from outside of this forum
                        John RegehrR This user is from outside of this forum
                        John Regehr
                        wrote last edited by
                        #24

                        @kaoudis @wizardengineer ah! I don't think I knew that. where are you at right now?

                        kaoudisK 1 Reply Last reply
                        0
                        • Janne MorenJ This user is from outside of this forum
                          Janne MorenJ This user is from outside of this forum
                          Janne Moren
                          wrote last edited by
                          #25

                          @rygorous @regehr
                          -flooks-like-math-if-you-squint

                          1 Reply Last reply
                          0
                          • John RegehrR John Regehr

                            I guess people are just going to keep discovering that you can't really make a C compiler do constant time

                            https://www.theregister.com/2026/02/09/compilers_undermine_encryption/

                            William D. JonesC This user is from outside of this forum
                            William D. JonesC This user is from outside of this forum
                            William D. Jones
                            wrote last edited by
                            #26

                            @regehr Maybe it's time to write new assemblers that complement NASM*.

                            * Or MASM; I wish NASM had an invoke keyword, like MASM, to abstract away calling conventions. Rather than writing a macro for it.

                            1 Reply Last reply
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                            • Andy GockeA This user is from outside of this forum
                              Andy GockeA This user is from outside of this forum
                              Andy Gocke
                              wrote last edited by
                              #27

                              @rygorous @regehr We've had a hell of a time with our macos ARM64 ASM. Last ~3 ld64 updates have all had reloc problems

                              1 Reply Last reply
                              0
                              • John RegehrR John Regehr

                                @kaoudis @wizardengineer ah! I don't think I knew that. where are you at right now?

                                kaoudisK This user is from outside of this forum
                                kaoudisK This user is from outside of this forum
                                kaoudis
                                wrote last edited by
                                #28

                                @regehr @wizardengineer Strava! I’m doing appsec over there

                                John RegehrR 1 Reply Last reply
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                                • kaoudisK kaoudis

                                  @regehr @wizardengineer Strava! I’m doing appsec over there

                                  John RegehrR This user is from outside of this forum
                                  John RegehrR This user is from outside of this forum
                                  John Regehr
                                  wrote last edited by
                                  #29

                                  @kaoudis @wizardengineer awesome!

                                  1 Reply Last reply
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                                  • John RegehrR John Regehr

                                    I guess people are just going to keep discovering that you can't really make a C compiler do constant time

                                    https://www.theregister.com/2026/02/09/compilers_undermine_encryption/

                                    Pierre H.M This user is from outside of this forum
                                    Pierre H.M This user is from outside of this forum
                                    Pierre H.
                                    wrote last edited by
                                    #30

                                    @regehr yes you can, unless you care about correct results too.

                                    1 Reply Last reply
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                                    • John RegehrR John Regehr

                                      I guess people are just going to keep discovering that you can't really make a C compiler do constant time

                                      https://www.theregister.com/2026/02/09/compilers_undermine_encryption/

                                      Tor LillqvistT This user is from outside of this forum
                                      Tor LillqvistT This user is from outside of this forum
                                      Tor Lillqvist
                                      wrote last edited by
                                      #31

                                      @regehr "The user types in a password, which gets checked against a database, character by character"

                                      Seriously? That is how they think it works?

                                      1 Reply Last reply
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