X-Recipient: archive-cygwin@delorie.com X-Spam-Check-By: sourceware.org Date: Fri, 1 Jul 2011 10:36:03 +0200 From: Corinna Vinschen To: cygwin@cygwin.com Subject: Re: Vim segv'ing Message-ID: <20110701083603.GM9552@calimero.vinschen.de> Reply-To: cygwin@cygwin.com Mail-Followup-To: cygwin@cygwin.com References: <20110630072012.GB9552@calimero.vinschen.de> <2BF01EB27B56CC478AD6E5A0A28931F202CFAFF7@A1DAL1SWPES19MB.ams.acs-inc.net> <20110630142353.GH9552@calimero.vinschen.de> <20110630150502.GJ9552@calimero.vinschen.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20110630150502.GJ9552@calimero.vinschen.de> User-Agent: Mutt/1.5.21 (2010-09-15) Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Delivered-To: mailing list cygwin@cygwin.com On Jun 30 17:05, Corinna Vinschen wrote: > On Jun 30 16:23, Corinna Vinschen wrote: > > On Jun 30 07:30, Nellis, Kenneth wrote: > > > > From: Corinna Vinschen > > > > Works fine for me. If I'm admin, writing works, if I'm not admin, > > > > writing fails with permission denied. Could you please send your > > > > cygcheck output per http://cygwin.com/problems.html as well as an > > > > strace which shows what happens, like this: > > > > > > > > $ strace -o vim.trace vim-nox /etc/hosts > > > > :wq! > > > > > > FWIW, I see the same problem as the OP. The strace command interferes > > > with vim so that it won't recognize ESC to allow the ":" to be > > > recognized, so I can't ":wq!" as requested. strace output nevertheless > > > attached as is cygcheck -svr output. > > > > You strace shows nothing, it just stops at one point. Are you running > > from a console or from mintty? When running in a console in default > > notty mode, :w! or :wq! works fine. Can you try again? Perhaps with > > other strace flags? > > > > strace -o vim.trace -m 0xffff vim-nox /etc/hosts > > I suddenly can reproduce the problem. For some reason it occurs only if > both, vim and the Cygwin DLL, are compiled with -O2. Darn. This does > not make debugging exactly easier :-P All I can say at this point is > that the stack gets overwritten at one point. FYI, I tracked it down to the place where the stack overwrite occurs. This is most puzzeling. When typing :wq!, the following chain of functions is called: nv_colon do_cmdline ex_exit do_write open <- Here it calls into the Cygwin DLL fhandler_base::open_with_arch fhandler_base::open_fs fhandler_base::open NtCreateFile <--Here it calls into NTDLL.DLL The open call tries to open the backup file "/etc/hosts~", not the symlink itself. In the optimized version of vim, the local variable "cap" in the function nv_colon is kept in register $esi. When do_cmdline is called, $esi is pushed onto the stack. Then everything goes its normal ways, until NtCreateFile is called. And here's the puzzler: This call to NtCreateFile overwrites the 4 byte stack slot in which the "cap" pointer is saved with the value 0x10c! After return from do_cmdline, nv_colon uses cap in an expression and since cap is a pointer value, when dereferencing the pointer, vim crashes. I checked this situation a couple of times in assembler. The cap value is fine up to the "call NtCreateFile@44", and it's changed to 0x10c when NtCreateFile returns. I don't understand that. Not only that NtCreateFile is not supposed to change values on the stack in the stack frame 8 functions above, I also don't know what the value 0x10c is. It's not the HANDLE returned by NtCreateFile, that's 0x1e4. Well, that's it. I just had to vent a bit since I have no idea how to proceed at this point. I can see and prove that the NtCreateFile call overwrites the stack, but it's totally unlikely that NtCreateFile would ever do that. The OS would be broken. Oh, and here's a last-minute surprise: It does not happen if you run gvim, rather than vim. Maybe I should just give up to provide packages. Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Project Co-Leader cygwin AT cygwin DOT com Red Hat -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple