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Re: Has "stack overflow" specified behavior?

From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c++
Subject Re: Has "stack overflow" specified behavior?
Date 2021-12-16 07:42 -0800
Organization A noiseless patient Spider
Message-ID <865yro4kub.fsf@linuxsc.com> (permalink)
References <f5624610-cbe0-4e27-9f52-f4a900172c89n@googlegroups.com> <sp61ti$phb$1@dont-email.me> <86czm05exm.fsf@linuxsc.com> <sp9kq1$iua$1@dont-email.me>

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Paavo Helde <eesnimi@osa.pri.ee> writes:

> 14.12.2021 00:16 Tim Rentsch kirjutas:
>
>> Paavo Helde <eesnimi@osa.pri.ee> writes:
>>
>>> 12.12.2021 10:42 wij kirjutas:
>>>
>>>> void t() {
>>>>     int a;
>>>>     ++a;
>>>>     t();
>>>> };
>>>>
>>>> int main()
>>>> {
>>>>    t();
>>>> }
>>>
>>> BTW, your example code is not guaranteed to cause stack overflow, it
>>> might go into an infinite loop instead because of tail recursion, or
>>> become a zero op by optimizing the whole t() function away, either
>>> as UB or as a code with no effect.
>>
>> It's important to distinguish the two realms of abstract machine
>> and actual machine.  In the abstract machine, the program shown
>> above (after fixing the problem of reading an uninitialized
>> variable) does have a well-defined specification, and the program
>> as a whole has defined behavior.  Whether a program has defined
>> behavior or undefined behavior is determined solely by what goes
>> on in the abstract machine (which may depend on values read from
>> a file or other input device, etc, but still the question is to
>> be answered considering only what happens in the abstract
>> machine, with reference to any actual machine).  Everything the
>> program does has a well-defined specification, and so the program
>> has only defined behavior, and no undefined behavior.
>
> You might be right in that after fixing the uninitialized memory
> reading bug the program would not contain UB.  Nevertheless, the
> standard gives explicit permission to a C++ implementation to optimize
> away such code with no observable side effects, making this whole
> program a non-op instead of an infinite CPU or memory eater:
>
> "6.9.2.2 Forward progress [intro.progress]
> 1 The implementation may assume that any thread will eventually do one
> of the following:
> (1.1) - terminate,
> (1.2) - make a call to a library I/O function,
> (1.3) - perform an access through a volatile glvalue, or
> (1.4) - perform a synchronization operation or an atomic operation.
> [Note:  This is intended to allow compiler transformations such as
> removal of empty loops, even when termination cannot be proven.  -end
> note]"

Yes, I noticed that before.  I didn't comment on it because, one,
it strikes me as incidental to the main question, and two, if we
change the example just slightly

    void t() {
        volatile int a = 0;
        ++a;
        t();
    };
    
    int main()
    {
       t();
    }

then the program cannot be optimized into nothingness, so we
still have the question of how an implementation is obliged to
treat this program.  And I think the answer is the same, that
implementations are obliged to try to carry it out faithfully but
are allowed to fail when they run out of memory.  Failure here
isn't the same as undefined behavior, because up to the point of
actually running out of memory everything is fine as far as the
abstract semantics are concerned.  To say that another way, it is
a well-established point that undefined behavior is allowed to
affect things "in the past", but here that freedom is not
granted.  The presence of volatile reads and writes means that
there are other consequences that could be observed, such as
program running time, so there isn't the same kind of freedom
as would be allowed for undefined behavior.

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Thread

Has "stack overflow" specified behavior? wij <wyniijj@gmail.com> - 2021-12-12 00:42 -0800
  Re: Has "stack overflow" specified behavior? Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-12 09:52 +0100
    Re: Has "stack overflow" specified behavior? red floyd <no.spam.here@its.invalid> - 2021-12-12 12:59 -0800
  Re: Has "stack overflow" specified behavior? Paavo Helde <eesnimi@osa.pri.ee> - 2021-12-13 01:51 +0200
    Re: Has "stack overflow" specified behavior? Juha Nieminen <nospam@thanks.invalid> - 2021-12-13 05:48 +0000
      Re: Has "stack overflow" specified behavior? Bo Persson <bo@bo-persson.se> - 2021-12-13 10:44 +0100
        Re: Has "stack overflow" specified behavior? wij <wyniijj@gmail.com> - 2021-12-13 04:44 -0800
        Re: Has "stack overflow" specified behavior? Richard Damon <Richard@Damon-Family.org> - 2021-12-13 07:47 -0500
          Re: Has "stack overflow" specified behavior? Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-14 08:32 +0100
            Re: Has "stack overflow" specified behavior? Richard Damon <Richard@Damon-Family.org> - 2021-12-14 07:49 -0500
              Re: Has "stack overflow" specified behavior? scott@slp53.sl.home (Scott Lurndal) - 2021-12-14 14:23 +0000
              Re: Has "stack overflow" specified behavior? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-12-14 16:16 +0100
        Re: Has "stack overflow" specified behavior? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-13 12:13 -0500
          Re: Has "stack overflow" specified behavior? Öö Tiib <ootiib@hot.ee> - 2021-12-13 12:05 -0800
            Re: Has "stack overflow" specified behavior? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-12-13 17:11 -0800
            Re: Has "stack overflow" specified behavior? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-12-13 19:00 -0800
              Re: Has "stack overflow" specified behavior? Öö Tiib <ootiib@hot.ee> - 2021-12-13 23:03 -0800
          Re: Has "stack overflow" specified behavior? Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-14 08:33 +0100
            Re: Has "stack overflow" specified behavior? David Brown <david.brown@hesbynett.no> - 2021-12-14 09:13 +0100
              Re: Has "stack overflow" specified behavior? Juha Nieminen <nospam@thanks.invalid> - 2021-12-14 10:09 +0000
                Re: Has "stack overflow" specified behavior? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-14 16:14 +0000
                Re: Has "stack overflow" specified behavior? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-12-14 15:23 -0800
              Re: Has "stack overflow" specified behavior? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-14 16:10 +0000
              Re: Has "stack overflow" specified behavior? Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-14 17:38 +0100
                Re: Has "stack overflow" specified behavior? scott@slp53.sl.home (Scott Lurndal) - 2021-12-14 17:09 +0000
                Re: Has "stack overflow" specified behavior? Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-14 18:39 +0100
                Re: Has "stack overflow" specified behavior? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-14 11:01 -0800
              Re: Has "stack overflow" specified behavior? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-14 10:52 -0800
                Re: Has "stack overflow" specified behavior? David Brown <david.brown@hesbynett.no> - 2021-12-14 20:15 +0100
            Re: Has "stack overflow" specified behavior? Richard Damon <Richard@Damon-Family.org> - 2021-12-14 07:59 -0500
          Re: Has "stack overflow" specified behavior? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-12-14 16:19 +0100
            Re: Has "stack overflow" specified behavior? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-14 11:33 -0500
      Re: Has "stack overflow" specified behavior? Manfred <noname@add.invalid> - 2021-12-13 17:23 +0100
      Re: Has "stack overflow" specified behavior? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2021-12-15 23:27 +0000
        Re: Has "stack overflow" specified behavior? David Brown <david.brown@hesbynett.no> - 2021-12-16 08:37 +0100
    Re: Has "stack overflow" specified behavior? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-13 14:16 -0800
      Re: Has "stack overflow" specified behavior? wij <wyniijj@gmail.com> - 2021-12-13 15:07 -0800
        Re: Has "stack overflow" specified behavior? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-16 05:53 -0800
          Re: Has "stack overflow" specified behavior? wij <wyniijj@gmail.com> - 2021-12-16 08:34 -0800
            Re: Has "stack overflow" specified behavior? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-16 12:17 -0800
              Re: Has "stack overflow" specified behavior? wij <wyniijj@gmail.com> - 2021-12-16 13:38 -0800
                Re: Has "stack overflow" specified behavior? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-16 14:15 -0800
            Re: Has "stack overflow" specified behavior? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-16 20:10 -0800
          Re: Has "stack overflow" specified behavior? Öö Tiib <ootiib@hot.ee> - 2021-12-16 14:14 -0800
            Re: Has "stack overflow" specified behavior? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-16 20:20 -0800
              Re: Has "stack overflow" specified behavior? Öö Tiib <ootiib@hot.ee> - 2021-12-17 08:46 -0800
      Re: Has "stack overflow" specified behavior? Paavo Helde <eesnimi@osa.pri.ee> - 2021-12-14 10:32 +0200
        Re: Has "stack overflow" specified behavior? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-16 07:42 -0800
          Re: Has "stack overflow" specified behavior? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-12-17 01:07 +0000
            Re: Has "stack overflow" specified behavior? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-17 01:28 +0000
            Re: Has "stack overflow" specified behavior? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-16 19:54 -0800
              Re: Has "stack overflow" specified behavior? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-12-17 10:06 +0000
  Re: Has "stack overflow" specified behavior? Manfred <noname@add.invalid> - 2021-12-13 17:08 +0100
    Re: Has "stack overflow" specified behavior? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-13 13:50 -0800
      Re: Has "stack overflow" specified behavior? Manfred <noname@add.invalid> - 2021-12-14 16:32 +0100
  Re: Has "stack overflow" specified behavior? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-13 13:13 -0800
  Re: Has "stack overflow" specified behavior? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-13 15:55 -0800
    Re: Has "stack overflow" specified behavior? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-13 15:58 -0800
    Re: Has "stack overflow" specified behavior? wij <wyniijj@gmail.com> - 2021-12-14 01:41 -0800

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