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Subject: Re: Bug: Synchronous signals broken on Cygwin 64
To: cygwin AT cygwin DOT com
References: <bc993d03-a9ac-d1c9-c33a-03cfc810edbe AT users DOT sourceforge DOT net>
From: Marco Atzeri <marco DOT atzeri AT gmail DOT com>
Message-ID: <c5ae3eb3-090e-3a3c-64c5-0abfb0b5b477@gmail.com>
Date: Thu, 26 Apr 2018 12:44:35 +0200
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On 4/26/2018 9:57 AM, Thomas Zimmermann wrote:
> Hello mailing list,
> 
> I noticed that synchronous signals (e.g., SIGSEGV, SIGFPE) appear to be
> broken on 64-bit Cygwin systems. I could not find additional information
> on the mailing list. If this is not already a known problem, you'll find
> some analysis below.
> 
> 
> I use Cygwin DLL 2.10 with all packages up-to-date. My test system runs
> Windows 7.
> 
> 
> The expected behavior is that an installed signal handler runs exactly
> once for a signal and the OS terminates the program if the handler
> returns. This works on 32-bit Cygwin. From my observation, Cygwin 64
> differs in the follow ways:
> 
> 1) Generating a synchronous signal on the main thread, makes the signal
> handler enter an endless loop. The attached test 'syncsig.c' illustrates
> this.
> 
> 2) Generating a synchronous signal on an additional POSIX thread ignores
> the installed signal handler entirely. The handler does not run and the
> program gets terminated immediately. The attached test 'syncsig_mt.c'
> illustrates this.
> 
> 
> As mentioned, both cases work correctly on 32-bit installations. I
> cannot point to the exact location of the problem, but it appears that
> the Cygwin exception-handler code is not set up by 64-bit code.
> 
> In case 2) I can see the Windows function KiUserExceptionDispatcher()
> being executed for the synchronous signal on the affected thread. This
> should lead to a call to the Cygwin exception handler. It does for
> 32-bit, but not for 64-bit code.

just for confirmation, same results and discrepancies on my W7

>  From what I've seen, the exception handler is installed in the c'tor
> exception::exception(). [exception.cc:138] The only invocation I found
> was in SetThreadName(). [miscfuncs.cc:951] This set-up code is 32-bit-only.
> 
> 
> BTW, is there a bug tracker for Cygwin? I'd open a bug report there, or
> add the information to an existing one.

there is no bug tracker. Bugs are managed on this mailing list.

> 
> Best regards
> Thomas
> 

Regards
Marco

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