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X-HELO: mailout04.t-online.de
Subject: Re: gcc-6.3.0-1 regression: libstdc++6 DLL breaks exception handling
To: cygwin AT cygwin DOT com
References: <6a80a46a-8de9-5d28-f7ef-897a53159603 AT t-online DOT de> <dcea951e-96f2-b592-4804-1c58abf84a83 AT gmail DOT com>
From: Christian Franke <Christian DOT Franke AT t-online DOT de>
Message-ID: <a4c62a64-5570-e39c-a8b5-d659fdbfbc6d@t-online.de>
Date: Tue, 7 Feb 2017 16:26:37 +0100
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JonY wrote:
> On 01/26/2017 10:30 AM, Christian Franke wrote:
>> After upgrading to gcc test version 6.3.0-1, C++ exception handling is
>> broken if DLL version of new libstdc++6 is used.
>>
> Noted, I'll consider the test version broken for now.
>
>

Meantime I examined the testcase with gdb: The DLL exports a bogus 
address for the symbol "_ZTIi" ('typeinfo for int'). This results in 
this more simple testcase:

#include <typeinfo>
int main() {
   const std::type_info & ti = typeid(int); // &_ZTIi from DLL
   const char * p = ti.name(); // segfaults because &_ZTIi is bogus.
}


And indeed, the export table of the DLL looks 'interesting'. The offsets 
of various exported symbols are apparently all 93980000:

$ objdump -p cygstdc++-6.dll

     [5142] +base[5143] c6760 Export RVA
     [5143] +base[5144] c6768 Export RVA
     [5144] +base[5145] 93980000 Export RVA
...
     [5151] +base[5152] 93980000 Export RVA
     [5152] +base[5153] 93980000 Export RVA
     [5153] +base[5154] 93980000 Export RVA
     [5154] +base[5155] 93980000 Export RVA
...
     [5167] +base[5168] 93980000 Export RVA
     [5168] +base[5169] c6780 Export RVA
...
[Ordinal/Name Pointer] Table
...
     [5143] _ZTISt9type_info
     [5144] _ZTIa
...
     [5151] _ZTIh
     [5152] _ZTIi
     [5153] _ZTIj
     [5154] _ZTIl
...
     [5167] _ZTSDs
     [5168] _ZTSN10__cxxabiv115__forced_unwindE

$  objdump -p cygstdc++-6.dll | grep -cw 93980000
759


Hmm... bug in the (bin)utils used to build the DLL?

Possibly related:
https://cygwin.com/ml/cygwin/2017-01/msg00375.html

Christian


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