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Date:	Mon, 28 Oct 2013 14:00:05 -0400
From:	Christopher Faylor <cgf-use-the-mailinglist-please AT sourceware DOT org>
To:	Pan ruochen <panruochen AT gmail DOT com>, gdb AT sourceware DOT org
Cc:	cygwin AT cygwin DOT com
Subject:	Re: Fwd: gdb on Cygwin cannot give correct call stacks for segment faults
Message-ID:	<20131028180005.GA5542@ednor.casa.cgf.cx>
Reply-To:	cygwin AT cygwin DOT com
Mail-Followup-To:	Pan ruochen <panruochen AT gmail DOT com>, gdb AT sourceware DOT org, cygwin AT cygwin DOT com
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On Mon, Oct 28, 2013 at 12:00:17PM +0800, Pan ruochen wrote:
>Hi All,
>
>I find that my gdb on Cygwin cannot dump correct call stacks while
>segment faults arise.

This isn't a failing of gdb.  It's a Cygwin problem.  It can't reliably
show backtraces when a SEGV happens in Cygwin DLL code.  This is a known
issue.

cgf

>Test code is as follows:
>--------------------------------------------------------------
>#include <stdio.h>
>#include <stdlib.h>
>
>void foo()
>{
>    FILE * volatile dev =NULL;
>    fprintf(dev, "Hello World!\n");
>}
>
>int main()
>{
>    foo();
>    return 0;
>}
>--------------------------------------------------------------
>
>And backtrace information is as follows:
>Program received signal SIGSEGV, Segmentation fault.
>0x61138b61 in _fwrite_r () from /usr/bin/cygwin1.dll
>(gdb) backtrace
>#0  0x61138b61 in _fwrite_r () from /usr/bin/cygwin1.dll
>#1  0x76bd1194 in WaitForSingleObjectEx ()
>   from /cygdrive/c/windows/syswow64/kernel32.dll
>#2  0x76bd1148 in WaitForSingleObject ()
>   from /cygdrive/c/windows/syswow64/kernel32.dll
>#3  0x610dd558 in sig_send(_pinfo*, siginfo_t&, _cygtls*) ()
>   from /usr/bin/cygwin1.dll
>#4  0x610303b4 in exception::handle(_EXCEPTION_RECORD*,
>_exception_list*, _CONTEXT*, void*) () from /usr/bin/cygwin1.dll
>#5  0x77a5b499 in ntdll!LdrRemoveLoadAsDataTable ()
>   from /cygdrive/c/windows/system32/ntdll.dll
>#6  0x0028a6ac in ?? ()
>#7  0x77a5b46b in ntdll!LdrRemoveLoadAsDataTable ()
>   from /cygdrive/c/windows/system32/ntdll.dll
>#8  0x0028a6ac in ?? ()
>#9  0x77a10133 in ntdll!KiUserExceptionDispatcher ()
>   from /cygdrive/c/windows/system32/ntdll.dll
>#10 0x0028a6ac in ?? ()
>#11 0x61138c75 in fwrite () from /usr/bin/cygwin1.dll
>#12 0x610d75e5 in _sigfe () from /usr/bin/cygwin1.dll
>#13 0x0000000d in ?? ()
>#14 0x00000000 in ?? ()
>
>does not give any useful clues where the segment faults arise.
>So what is wrong?
>
>-- BR, Ruochen
>

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