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Message-ID: <3FC76805.1050601@inf.ethz.ch>
Date: Fri, 28 Nov 2003 16:21:41 +0100
From: Fabrice Marchal <fmarchal AT inf DOT ethz DOT ch>
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To: cygwin AT cygwin DOT com
Subject: Re: Code generation bug for operator new[] when -fcheck-new in GCC
 3.3.1
References: <000001c3b5c2$bad46370$6400a8c0 AT DELL2K>
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This looks similar to the problem I have with gcc 3.31 and mysql:
my code crashes after a constructor() as well. But it works on Linux 
(with gcc 3.3.1),
so is it a cygwin or gcc-on-cygwin problem?

Tom Scott wrote:

>This bug is more properly a bug with GCC and not with cygwin - it shows up
>in GCC 3.2.2 (i386-redhat-linux) as well. So I've submitted the problem to
>GCC Bugzilla.  It's Bug 13215. - Tom
>
>-----Original Message-----
>From: Tom Scott [mailto:tscott AT StorageMatrix DOT com] 
>Sent: Wednesday, November 26, 2003 4:17 PM
>To: cygwin AT cygwin DOT com
>Subject: Code generation bug for operator new[] when -fcheck-new in GCC
>3.3.1
>
>
>I've found that the following sample, which uses nothrow memory allocation
>semantics, generates a segmentation violation:
>
>// g++ -g -fcheck-new -fno-exceptions -fno-rtti sample.cpp #include
><stdlib.h>
> 
>class foo {
>public:
>    int v;
>    foo(){ v = 0; }
>    ~foo() {}
>    void* operator new[](size_t size) {
>        return 0;   // simulated memory failure
>    }
>    void operator delete[](void* p, size_t size) { }
>};
> 
>main()
>{
>    foo *p = new foo[2];
>    // p==4 here
>    if (p) delete [] p;
>    return 0;
>}
>
>The segmentation violation results from a bug in the code that is generated
>to call operator new[].  The return of operator new[] is correctly checked
>for non-zero before calling the ctor ("-fcheck-new" semantics), but this
>return value is subsequently incremented by 4.  As a result, p is set to 4
>(not 0) when memory runs out.
> 
>A work around is to modify applications so that the return value of "new
>class[]" is checked and to treat a return of 4 the same as 0.
> 
>Tom
>
>
>--
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>
>
>  
>


-- 
========================================================================
Fabrice Marchal           http://www.inf.ethz.ch/~marchal 
fabrice DOT marchal AT ieee DOT org  marchal AT inf DOT ethz DOT ch         +41-(0)1-632-56-79
ETH Zurich, CoLab Computational Laboratory        FAX:+41-(0)1-632-17-03
========================================================================



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