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Re: signal() anomaly

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On 08/01/2012 04:47 PM, hip cat wrote:
> On Wed, 01 Aug 2012 15:33:20 -0400, James Kuyper wrote:
...
>> Well, as "Nobody" has already pointed out, that's not an option. Using
>> SIG_IGN for this has undefined behavior. So does registering your own
>> SIGSEGV "handler" that doesn't bother to actually do anything, and
>> simply returns. Therefore, you're going to have to either insert the
>> null checks, or let the program abort() - your choice.
> 
> Word Jim,
> 
> I think Eric was right on the money asking about the return value. If the 
> signal() call returns success, but the "ignore" is ignored, I say that's 
> a bug in the C library. I think I'll file a bug report against glibc.

The C standard specifies that dereferencing a null pointer  has
undefined behavior. One of the possibilities allowed by that fact is
that a SIGSEGV signal is raised, but the standard does not require that
it be raised. Whether or not that signal is raised, and regardless of
whether the SIGSEGV handler has been set to SIG_IGN, SIG_DFL, or an
actual signal handler, the behavior of your program remains undefined by
the C standard. It doesn't matter what the signal handler actually does,
the behavior of your program became undefined as soon as it dereferenced
a null pointer.

The POSIX standard does specify that a SIGSEGV signal be raised, but
specifies that the behavior of your program is undefined if that signal
is ignored, or if the signal handler returns.

"undefined behavior" means that anything is permitted, including
aborting your program. Your program aborted, which is one of the
permitted behaviors. On what grounds are you going to report a bug? What
requirement of any standard is violated by the fact that your program
aborted?

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signal() anomaly hip cat <nospam@nospam.com> - 2012-07-31 20:13 +0000
  Re: signal() anomaly Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-31 16:35 -0400
    Re: signal() anomaly hip cat <nospam@nospam.com> - 2012-08-01 18:59 +0000
    Re: signal() anomaly Nick Bowler <nbowler@draconx.ca> - 2012-08-01 20:14 +0000
  Re: signal() anomaly falk@rahul.net (Edward A. Falk) - 2012-07-31 22:12 +0000
    Re: signal() anomaly hip cat <nospam@nospam.com> - 2012-08-01 18:58 +0000
      Re: signal() anomaly James Kuyper <jameskuyper@verizon.net> - 2012-08-01 15:33 -0400
        Re: signal() anomaly hip cat <nospam@nospam.com> - 2012-08-01 20:47 +0000
          Re: signal() anomaly Paul <nospam@needed.com> - 2012-08-01 17:34 -0400
            Re: signal() anomaly Johann Klammer <klammerj@NOSPAM.a1.net> - 2012-08-02 06:34 +0200
              Re: signal() anomaly Paul <nospam@needed.com> - 2012-08-02 07:10 -0400
          Re: signal() anomaly Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-01 18:07 -0400
            Re: signal() anomaly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-08-02 00:15 +0100
              Re: signal() anomaly Nick Bowler <nbowler@draconx.ca> - 2012-08-02 00:05 +0000
                Re: signal() anomaly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-08-02 02:47 +0100
          Re: signal() anomaly James Kuyper <jameskuyper@verizon.net> - 2012-08-01 18:13 -0400
          Re: signal() anomaly James Kuyper <jameskuyper@verizon.net> - 2012-08-01 18:14 -0400
          Re: signal() anomaly Nobody <nobody@nowhere.com> - 2012-08-02 12:52 +0100
      Re: signal() anomaly Angel <angel+news@spamcop.net> - 2012-08-01 19:41 +0000
      Re: signal() anomaly Kenneth Brody <kenbrody@spamcop.net> - 2012-08-01 16:16 -0400
      Re: signal() anomaly Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-01 16:33 -0400
      Re: signal() anomaly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-08-02 00:22 +0100
      Re: signal() anomaly Stephen Sprunk <stephen@sprunk.org> - 2012-08-02 00:55 -0500
        Re: signal() anomaly Ike Naar <ike@sverige.freeshell.org> - 2012-08-02 07:01 +0000
      Re: signal() anomaly Öö Tiib <ootiib@hot.ee> - 2012-09-08 20:53 -0700
  Re: signal() anomaly Nobody <nobody@nowhere.com> - 2012-08-01 18:06 +0100
    Re: signal() anomaly Tim Rentsch <txr@alumni.caltech.edu> - 2012-09-07 13:44 -0700
  Re: signal() anomaly Kleuske <kleuske@nowhere.net> - 2012-08-02 20:52 +0000

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