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From: bangerth@dealii.org
To: gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
	massimo.ravasi@epfl.ch, nobody@gcc.gnu.org
Subject: Re: c++/8543: bus error with 2 word alignments
Date: Sat, 23 Nov 2002 00:30:00 -0000	[thread overview]
Message-ID: <20021118181227.14712.qmail@sources.redhat.com> (raw)

Synopsis: bus error with 2 word alignments

State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Mon Nov 18 10:11:12 2002
State-Changed-Why:
    I can confirm this. However, from my limited understanding,
    what you do is not legal. You try something like
      long long i;
      long long *p = (long long *)((char*)&i + 4);
      *p = 0;
    As far as I can tell, trying to play games with pointers
    and not obeying to the alignment rules of the types they
    point to is invoking undefined behavior, and a bus error
    is undefined behavior.
    
    That you get varying results with various flags and other
    parts of code is to be expected then (after all, a working
    program is a valid interpretation of "undefined behavior").
    
    Maybe someone can clarify on the pointer alignment issue?

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8543


             reply	other threads:[~2002-11-18 18:12 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-11-23  0:30 bangerth [this message]
  -- strict thread matches above, loose matches on Subject: below --
2003-01-23 15:05 nathan
2002-11-25 15:46 Wolfgang Bangerth
2002-11-25 15:36 Wolfgang Bangerth
2002-11-25 14:55 Wolfgang Bangerth
2002-11-19 13:36 massimo.ravasi

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