Re: GCC hasn't even gotten around to sequencing argument evaluation

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c++
Subject	Re: GCC hasn't even gotten around to sequencing argument evaluation
Date	2022-04-04 12:15 +0200
Organization	A noiseless patient Spider
Message-ID	<t2eggf$pm7$1@dont-email.me> (permalink)
References	(3 earlier) <t29mij$1bk8$1@gioia.aioe.org> <t29q1c$hf1$1@dont-email.me> <t29qms$18lf$1@gioia.aioe.org> <t2a4jh$6dj$1@dont-email.me> <t2e9to$rf2$1@gioia.aioe.org>

Show all headers | View raw

On 04/04/2022 10:23, Muttley@dastardlyhq.com wrote:
> On Sat, 2 Apr 2022 11:27:59 -0700
> Andrey Tarasevich <andreytarasevich@hotmail.com> wrote:
>> On 4/2/2022 8:39 AM, Muttley@dastardlyhq.com wrote:
>>> Undefined simply means no one cared enough to define it. The compiler writers
>>
>>> would have to deliberately change their parameter parsing and stack pushing
>>> code in order to crash in this instance.
>>>
>>
>> Oh yes, they would!
>>
>> Try this in GCC
>>
>>     int &foo()
>>     {
>>       int a = 42;
>>       return a;   // Undefined behavior
>>     }
>>
>>     int main()
>>     {
>>       std::cout << foo() << std::endl;
>>     }
>>
>> This is a different example of undefined behavior. This code will
>> segfault in GCC because the compiler writers decided to _deliberately_
>> return "null reference" from the above function. They didn't have to.
>> Yet they did so on purpose: to deliberately punish those who have a
>> habit of gratuitously returning references/pointers to local variables.

I would suppose the code deliberately returns a null reference to avoid 
a glaring security hole that might be abused.  (I don't expect it could 
be abused in this limited example, but invalid stack references 
certainly have been used for attacks in some cases.)  It's better to 
have a program crash quickly on such bugs than have the risk of hidden 
security flaws.

Note that gcc warns you about the problem - even if you don't enable 
warnings.

Newer versions of gcc will generate the "ud2" instruction (on x86-64) 
when you attempt to read the value of "foo()".  This forces an 
"undefined behaviour" fault.

> 
> Seems a good idea to me given otherwise it would be a bug that would probably
> remain hidden causing random behaviour until someone spent time tracking it
> down.
> 

Yes, at least in this case.

>> opportunity. An equivalent definition of undefined behavior says: the
>> compilers are allowed to translate the code under assumption that
>> undefined behavior never happens.
> 
> Except if it can be written in code then at some point it will happen.
> 

That is not even /remotely/ true.

gcc even has a way "__builtin_unreachable()" to specifically say that 
code flow cannot reach a particular point, and this is handled 
internally in /precisely/ the same way as undefined behaviour.

Thread

GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-01 20:34 -0700
  Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-04-02 10:19 +0200
    Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Bo Persson <bo@bo-persson.se> - 2022-04-02 12:19 +0200
    Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-02 14:18 +0200
  Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Gollwitzer <auriocus@gmx.de> - 2022-04-02 12:30 +0200
    Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? David Brown <david.brown@hesbynett.no> - 2022-04-02 14:12 +0200
      Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-02 14:20 +0200
      Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-02 14:28 +0000
        Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-02 17:27 +0200
          Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-02 15:39 +0000
            Re: GCC hasn't even gotten around to sequencing argument evaluation Barry Schwarz <schwarzb@delq.com> - 2022-04-02 09:15 -0700
              Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 08:21 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 12:02 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 14:42 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-04 08:49 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:18 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 08:37 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:54 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-06 11:24 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation Juha Nieminen <nospam@thanks.invalid> - 2022-04-06 10:49 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-06 18:21 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2022-04-06 15:40 +0100
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-06 15:00 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2022-04-06 17:03 +0100
                Re: GCC hasn't even gotten around to sequencing argument evaluation Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2022-04-06 17:18 +0100
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-07 08:58 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-07 11:01 -0400
                Re: GCC hasn't even gotten around to sequencing argument evaluation "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-04-06 23:13 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-07 09:11 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-06 10:53 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-06 14:50 -0400
                Re: GCC hasn't even gotten around to sequencing argument evaluation Sams Lara <samlara622@gmail.com> - 2022-04-06 22:27 +0100
                Re: GCC hasn't even gotten around to sequencing argument evaluation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-06 14:51 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Sams Lara <samlara622@gmail.com> - 2022-04-06 22:59 +0100
                Re: GCC hasn't even gotten around to sequencing argument evaluation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-06 15:54 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Öö Tiib <ootiib@hot.ee> - 2022-04-06 15:11 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-04-09 09:38 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-06 23:48 -0400
                Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-06 18:39 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-06 23:49 -0400
                Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-05 08:55 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 10:23 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-05 14:36 -0400
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-04 12:27 -0400
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:21 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 08:41 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:50 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 10:19 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-05 14:33 -0400
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-05 14:28 -0400
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 18:29 +0200
            Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-02 11:27 -0700
              Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 08:23 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 12:15 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 14:43 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 18:34 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:23 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 08:38 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-05 15:49 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-05 11:31 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation scott@slp53.sl.home (Scott Lurndal) - 2022-04-05 22:45 +0000
            Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-02 23:34 -0400
              Re: GCC hasn't even gotten around to sequencing argument evaluation Manfred <noname@add.invalid> - 2022-04-03 17:43 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-03 15:40 -0400
              Re: GCC hasn't even gotten around to sequencing argument evaluation Muttley@dastardlyhq.com - 2022-04-04 08:24 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-04-04 12:01 -0400
            Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-03 13:02 +0200
              Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-03 04:46 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Öö Tiib <ootiib@hot.ee> - 2022-04-03 07:02 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-03 11:30 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-03 21:20 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-03 12:49 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-04 00:40 +0300
                Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-03 15:40 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 09:13 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 09:02 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-04 02:07 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 13:28 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-04 06:01 -0700
                Re: GCC hasn't even gotten around to sequencing argument evaluation David Brown <david.brown@hesbynett.no> - 2022-04-04 19:11 +0200
                Re: GCC hasn't even gotten around to sequencing argument evaluation scott@slp53.sl.home (Scott Lurndal) - 2022-04-04 17:59 +0000
                Re: GCC hasn't even gotten around to sequencing argument evaluation Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-05 06:55 -0700
              Re: GCC hasn't even gotten around to sequencing argument evaluation Manfred <noname@add.invalid> - 2022-04-03 18:39 +0200
        Re: GCC hasn't even gotten around to sequencing argument evaluation Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-03 09:09 +0300
      Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manfred <noname@add.invalid> - 2022-04-02 19:53 +0200
        Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? David Brown <david.brown@hesbynett.no> - 2022-04-03 13:45 +0200
          Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manfred <noname@add.invalid> - 2022-04-03 17:27 +0200
      Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-04-02 21:17 +0100
        Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manfred <noname@invalid.add> - 2022-04-02 23:04 +0200
          Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-04-03 00:22 +0100
        Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-02 17:33 -0700
          Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-04-03 14:23 +0100
          Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-04-06 08:31 -0700
            Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-06 11:05 -0700
              Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-04-25 03:32 -0700
    Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-02 11:18 -0700
  Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? David Brown <david.brown@hesbynett.no> - 2022-04-02 13:11 +0200
  Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manu Raju <MR@invalid.invalid> - 2022-04-02 18:26 +0100
  Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manu Raju <MR@invalid.invalid> - 2022-04-02 21:46 +0100
    Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-02 17:35 -0700
  Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Language Lawyer <language.lawyer@gmail.com> - 2022-04-04 02:28 -0700
    Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-04 05:52 -0700
      Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Language Lawyer <language.lawyer@gmail.com> - 2022-06-21 03:36 -0700
  Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Juha Nieminen <nospam@thanks.invalid> - 2022-04-04 10:48 +0000
    Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-04 05:49 -0700
      Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Juha Nieminen <nospam@thanks.invalid> - 2022-04-05 06:34 +0000
        Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-04-05 10:20 +0100
        Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-05 07:51 -0700
          Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Manfred <noname@add.invalid> - 2022-04-05 17:53 +0200
  Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Hanné <the.hanne@gmail.com> - 2022-04-10 06:06 +0200
    Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-09 21:20 -0700
    Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-04-09 21:39 -0700
      Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-09 22:34 -0700
        Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Hanné <the.hanne@gmail.com> - 2022-04-10 09:19 +0200
          Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? David Brown <david.brown@hesbynett.no> - 2022-04-10 12:21 +0200
            Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Hanné <the.hanne@gmail.com> - 2022-04-10 12:47 +0200
          Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-04-11 12:18 -0700
            Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-11 12:33 -0700
      Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Christian Hanné <the.hanne@gmail.com> - 2022-04-10 09:20 +0200
        Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-04-11 12:32 -0700
          Re: GCC hasn't even gotten around to sequencing argument evaluation yet??? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-11 15:11 -0700

csiph-web