Re: srand(0)

From	Michael S <already5chosen@yahoo.com>
Newsgroups	comp.lang.c
Subject	Re: srand(0)
Date	2025-12-31 15:15 +0200
Organization	A noiseless patient Spider
Message-ID	<20251231151502.00002c3e@yahoo.com> (permalink)
References	(10 earlier) <10ilfqp$2fs21$1@dont-email.me> <10ivq6b$1j8r3$1@dont-email.me> <q2V4R.913844$ACS3.500160@fx17.iad> <10j206j$27s3j$1@dont-email.me> <87jyy3wcgf.fsf@example.invalid>

Show all headers | View raw

On Tue, 30 Dec 2025 19:35:12 -0800
Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:

> Michael Sanders <porkchop@invalid.foo> writes:
> > On Tue, 30 Dec 2025 18:42:30 GMT, Scott Lurndal wrote:  
> >> What if 'argv[0]' is NULL (and argc == 0)?  
> >
> > Well, seems we have to make a choice, ISO vs. POSIX:
> >
> > *ISO C (C17 / C23)*:
> >
> > C17, 5.1.2.2.1 "Program startup"
> >
> > The value of argc shall be nonnegative.
> >
> > argv[argc] shall be a null pointer.  
> 
> [...]
> 
> > *POSIX.1-2017 (and later)*
> >
> > POSIX execve() specification:
> >
> > The argument argv is an array of character pointers
> > to null-terminated strings.
> >
> > The application shall ensure that argv[0] points to a filename
> > string that is associated with the process being started.  
> 
> [...]
> 
> > What say you?  
> 
> It happens that I recently spent some time looking into this.
> 
> As you say, POSIX requires argc >= 1, but ISO C only guarantees
> argc >= 0.
> 
> If argc == 0, a program that assumes argv[0] is non-null
> can run into serious problems if that assumption is invalid.
> In particular, a program called "pkexec" would try to traverse
> arguments starting with argv[1], which logically doesn't
> exist if argc==0.  Due to the way program arguments are laid
> out in memory, argv[1] is also envp[0].  Frivolity ensued.
> See <https://nvd.nist.gov/vuln/detail/cve-2021-4034>.
> 
> The Linux kernel updated execve to ensure that the invoked program
> has argc>=1.  It was patched in early 2022.  NetBSD still has this
> vulnerability.
> 
> Summary: Some systems guarantee that argc>=1 and argv[0] points to
> a valid string, but software that's intended to be portable should
> tolerate argc==0 and argv[0]==NULL.
> 
> For more information, see
> <https://github.com/Keith-S-Thompson/argv0>.
> 

If you are interested in behavior on non-POSIX systems, primarily
Windows, but possibly others as well (e.g. VMS) then using exec() in 
caller sounds like a bad idea. It just not how these systems work and
not how people write programs on them.
Even when exec() *appears* to works in some environments (like
msys2) it likely emulated by spawn() followed by exit().

I'd implement caller with spawn(). I suppose that even on POSIX it is
more idiomatic.

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-22 08:48 +0000
  Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-12-22 06:44 -0500
    Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 13:18 +0100
      Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-12-22 12:13 -0500
        Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 18:41 +0100
          Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-22 20:45 +0200
            Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-22 21:16 +0000
            Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 22:19 +0100
            Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 22:57 +0100
              Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-23 11:18 +0200
                Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-23 10:54 +0100
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-23 13:50 +0200
                Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-12-23 18:29 -0500
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-23 16:30 -0800
            Re: srand(0) antispam@fricas.org (Waldek Hebisch) - 2025-12-23 17:54 +0000
              Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 00:08 +0200
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-24 02:02 +0000
                Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-12-23 23:43 -0500
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-24 05:34 +0000
                Re: srand(0) antispam@fricas.org (Waldek Hebisch) - 2025-12-24 09:00 +0000
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 12:12 +0200
                Article of Melissa O'Nail (Was: srand(0)) Michael S <already5chosen@yahoo.com> - 2025-12-28 02:44 +0200
                Re: Article of Melissa O'Nail antispam@fricas.org (Waldek Hebisch) - 2025-12-28 05:38 +0000
                Re: Article of Melissa O'Nail Michael S <already5chosen@yahoo.com> - 2025-12-28 12:35 +0200
                Re: Article of Melissa O'Nail Michael S <already5chosen@yahoo.com> - 2026-01-05 14:21 +0200
                Re: Article of Melissa O'Nail antispam@fricas.org (Waldek Hebisch) - 2026-01-07 10:51 +0000
                Re: Article of Melissa O'Nail Michael S <already5chosen@yahoo.com> - 2026-01-08 14:03 +0200
                Re: Article of Melissa O'Nail Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-08 09:40 -0800
                Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-08 09:26 -0800
                Re: srand(0) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-12-24 13:48 -0800
                Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-07 08:41 -0800
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-08 01:06 +0200
              Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-24 05:22 -0600
                Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-24 23:09 -0600
                Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-25 09:51 +0100
                Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-25 04:24 -0600
              Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-07 07:50 -0800
            Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-07 07:46 -0800
              Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-07 18:14 +0200
          Re: srand(0) Kaz Kylheku <046-301-5902@kylheku.com> - 2025-12-22 19:16 +0000
            Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-22 22:35 +0100
      Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 07:24 +0000
        Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-23 09:59 +0100
          Re: srand(0) Michael Bäuerle <michael.baeuerle@stz-e.de> - 2025-12-23 11:09 +0100
            Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 14:49 +0000
          Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-23 16:13 +0000
            Re: srand(0) richard@cogsci.ed.ac.uk (Richard Tobin) - 2025-12-23 19:05 +0000
        Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-23 02:16 -0800
          Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 14:47 +0000
        Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-23 16:08 +0000
          Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 15:44 +0000
    Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 07:17 +0000
      Re: srand(0) David Brown <david.brown@hesbynett.no> - 2025-12-23 08:25 +0100
        Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 14:45 +0000
          Re: srand(0) David Brown <david.brown@hesbynett.no> - 2025-12-23 19:15 +0100
  Re: srand(0) John McCue <jmclnx@gmail.com.invalid> - 2025-12-23 00:39 +0000
    Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-23 02:17 +0000
      Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 14:55 +0000
        Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-24 23:35 -0600
          Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-26 08:23 +0000
            Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-26 14:48 -0600
              Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-26 15:12 -0600
    Re: srand(0) Ike Naar <ike@sdf.org> - 2025-12-23 06:49 +0000
      Re: srand(0) John McCue <jmclnx@gmail.com.invalid> - 2025-12-23 20:37 +0000
        Re: srand(0) Ike Naar <ike@sdf.org> - 2025-12-24 15:22 +0000
    Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-23 07:25 +0000
      Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-24 06:16 +0000
        Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 15:21 +0000
          Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-24 19:00 +0000
            Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-25 03:07 -0600
              Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-25 19:31 +0000
                Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-25 21:14 +0100
                Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-25 15:29 -0600
                Re: srand(0) Paul <nospam@needed.invalid> - 2025-12-25 23:25 -0500
                Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-25 23:41 -0600
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-26 05:42 +0000
                Re: srand(0) Paul <nospam@needed.invalid> - 2025-12-26 01:52 -0500
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-26 07:56 +0000
                Re: srand(0) BGB <cr88192@gmail.com> - 2025-12-26 04:48 -0600
      Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 10:51 +0200
        Re: srand(0) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-12-24 00:59 -0800
        Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 15:28 +0000
          Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 17:44 +0200
            Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 16:17 +0000
              Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-24 17:53 +0100
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 17:27 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 17:33 +0000
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-24 20:16 +0200
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-25 02:01 +0000
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-25 03:17 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-26 08:13 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-25 04:30 +0000
                Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-25 09:10 +0100
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-26 08:08 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-30 06:07 +0000
                Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-30 18:42 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-31 02:01 +0000
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 03:10 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-31 03:28 +0000
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 09:37 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-01 07:32 +0000
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 19:02 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-01 19:20 +0000
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-01 21:53 +0200
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 23:50 +0000
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-02 14:32 +0200
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-02 16:18 +0200
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-02 20:52 +0000
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-02 20:46 +0000
                Re: srand(0) Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2026-01-03 04:08 +0000
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-03 04:39 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-03 14:24 +0000
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-03 20:38 +0200
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-30 19:37 -0800
                Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-31 17:24 +0000
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:17 -0800
                Re: srand(0) Paul <nospam@needed.invalid> - 2025-12-31 12:30 -0500
                Re: srand(0) bart <bc@freeuk.com> - 2025-12-31 18:42 +0000
                Re: srand(0) Paul <nospam@needed.invalid> - 2025-12-31 15:07 -0500
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-31 22:18 +0200
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 20:55 +0000
                Re: srand(0) bart <bc@freeuk.com> - 2025-12-31 22:57 +0000
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 16:00 -0800
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 01:03 +0000
                Re: srand(0) bart <bc@freeuk.com> - 2026-01-01 14:05 +0000
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 19:03 +0000
                Re: srand(0) bart <bc@freeuk.com> - 2026-01-01 20:28 +0000
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:29 -0800
                Re: srand(0) highcrew <high.crew3868@fastmail.com> - 2026-01-01 00:31 +0100
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 16:05 -0800
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-31 15:29 +0200
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 20:52 +0000
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:14 -0800
                Re: srand(0) Geoff <geoff@invalid.invalid> - 2026-01-05 20:00 -0800
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:03 -0800
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-30 19:35 -0800
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-31 04:51 +0000
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2025-12-31 15:15 +0200
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-31 20:51 +0000
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 15:00 -0800
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-01-01 01:45 +0200
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-12-31 16:34 -0800
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-01 07:23 +0000
                Re: srand(0) Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2026-01-01 02:01 +0000
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-01 02:29 +0000
                Re: srand(0) Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-12-30 06:34 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-30 14:05 +0000
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-28 05:51 +0000
            Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2025-12-24 17:08 +0000
    Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-07 07:39 -0800
      Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-07 13:54 -0800
        Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-08 15:34 +0000
          Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-08 14:44 -0800
            Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-09 06:06 +0000
              Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-08 22:46 -0800
                Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-09 22:38 +0000
                Re: srand(0) scott@slp53.sl.home (Scott Lurndal) - 2026-01-09 23:27 +0000
                Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-09 17:09 -0800
                Re: srand(0) Kaz Kylheku <046-301-5902@kylheku.com> - 2026-01-10 19:44 +0000
        Re: srand(0) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-09 00:36 -0800
  Re: srand(0) Bonita Montero <Bonita.Montero@gmail.com> - 2025-12-23 11:04 +0100
  Re: srand(0) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-12-23 21:44 -0800
    Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-24 15:41 +0000
      Re: srand(0) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-12-24 18:04 +0100
        Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2025-12-25 05:41 +0000
  Re: srand(0) Michael Sanders <porkchop@invalid.foo> - 2026-01-08 02:57 +0000

csiph-web