X-Spam-Check-By: sourceware.org Date: Wed, 29 Mar 2006 19:06:56 -0500 From: Christopher Faylor To: cygwin AT cygwin DOT com Subject: Re: dlopen() bug (new testcase) Message-ID: <20060330000656.GE12890@trixie.casa.cgf.cx> Reply-To: cygwin AT cygwin DOT com Mail-Followup-To: cygwin AT cygwin DOT com References: <469738104 AT web DOT de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <469738104@web.de> User-Agent: Mutt/1.5.11 Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm Precedence: bulk List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner AT cygwin DOT com Mail-Followup-To: cygwin AT cygwin DOT com Delivered-To: mailing list cygwin AT cygwin DOT com Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by delorie.com id k2U072g0024148 On Thu, Mar 30, 2006 at 01:35:54AM +0200, Bernhard Loos wrote: >> -----Urspr?ngliche Nachricht----- >> Von: Christopher Faylor >> Gesendet: Wed, 29 Mar 2006 18:15:34 -0500 >>On Thu, Mar 30, 2006 at 01:10:56AM +0200, Bernhard Loos wrote: >>>I looked at the problem again this week, but unfortunately I'm unable >>>to debug anything happening after the first SIGSEGV. I inserted a view >>>OutputDebugString()-calls and got those results: >>> >>>00:00:00.703: LoadLibraryA("H:\cygwin\test\CrashTest\CrashTest.dll") called from "CYGWIN1.DLL" at address 0x6100FE42 by thread 1. >>>00:00:00.718: Loaded "CRASHTEST.DLL" at address 0x003F0000 by thread 1. Successfully hooked module. >>>00:00:00.718: DllMain(0x003F0000, DLL_PROCESS_ATTACH, 0x00000000) in "CRASHTEST.DLL" called by thread 1. >>>00:00:00.718: myfault::faulted >>>00:00:00.718: setup_fault >>>00:00:00.718: First chance exception 0xC0000005 (Access Violation) occurred in "CYGWIN1.DLL" at address 0x610B2DE2 by thread 1. >>>00:00:00.718: Unloaded "CRASHTEST.DLL" at address 0x003F0000 by thread 1. >>>00:00:00.718: LoadLibraryA("H:\cygwin\test\CrashTest\CrashTest.dll") returned NULL by thread 1. Error: Unzulssiger Zugriff auf einen Speicherbereich (998). >>>00:00:00.781: First chance exception 0xC0000005 (Access Violation) occurred at address 0x003F101A by thread 1. >>>00:00:00.781: return_from_fault >>>00:00:00.781: First chance exception 0xC0000005 (Access Violation) occurred at address 0x40000060 by thread 1. >>>00:00:00.781: First chance exception 0xC0000029 (Unknown) occurred in "NTDLL.DLL" at address 0x7C95EB28 by thread 1. >>> >>>It looks, like Windows unloads the DLL after the first exception even before the myfault-exception handler is able to catch it. >>>So return_from_fault() tries to longjmp to code wich isn't present any more an the second exception occurs. >>> >>>To fix this problem, I would suggest to use the IsBadReadPtr()-function instead of the myfault-exception handler to check the pointer in >>>verifyable_object_isvalid(). >>>I could write a patch, if nobody has any objections. >> >>Sorry, no. We *just* got rid of IsBadReadPtr's. > >Just out of interest, what's the problem with IsBadReadPtr? You'll have to read the archives. Eric Blake has talked about this very recently. >>FWIW, I doubt that Windows is really ignoring an exception handler. > >The exception handler is called, but at least the return_from_fault is >called after the DLL gets unloaded, as you can see above. I don't see that in your output. However, If that was the case, you should be able to set a breakpoint in the exception handler to verify it without resorting to contortions like adding OutputDebugString. cgf -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/