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Date:	Thu, 30 Mar 2006 01:10:56 +0200
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From:	Bernhard Loos <bernloos AT web DOT de>
To:	cygwin AT cygwin DOT com
Subject:	Re: dlopen() bug (new testcase)
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Hello
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.

                Bernhard

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