On 18/07/2013 20:59, Ken Brown wrote: > On 7/17/2013 5:31 PM, Jon TURNEY wrote: >> >> On 19/06/2013 23:39, Yaakov (Cygwin/X) wrote: >>> There appears to be a bug in the MIT-SHM extension with the 64-bit >>> xserver; both XWin and Xvfb have manifested this so far. The easiest way to >>> trigger this is to install gnome-themes-standard, add >>> gtk-theme-name="Adwaita" to your ~/.gtkrc-2.0, then start a GTK+2 program >>> (e.g. gtk-demo), but GTK+3 programs also show this. Starting the server >>> with -extension MIT-SHM, or using a 32-bit server even with MIT-SHM, works >>> fine. >> >> On 06/07/2013 15:28, Jon TURNEY wrote: >>> On 06/07/2013 12:46, Ken Brown wrote: >>>> On 64bit Cygwin, if I try to run emacs under X11 while cygserver is >>>> running, >>>> emacs fails to connect to the X server. The error message from the X >>>> server is >>>> >>>> BadShmSeg (invalid shared segment parameter) on protocol request 131 >>>> >>>> To reproduce: >>>> >>>> 1. Install the current version of emacs-X11 (24.3-4). >>>> >>>> 2. Start the (64bit) cygserver service. >>>> >>>> 3. Start the (64bit) X server, e.g., by typing "startxwin" in a Cygwin >>>> Terminal. >>>> >>>> 4. In the resulting xterm, try to start emacs: >>>> >>>> $ emacs-X11.exe -Q & >>>> >>>> The result is that emacs displays the error message above and then aborts. >>>> >>>> emacs-X11 works fine if the X server is started when cygserver is not >>>> running. >>> >>> Yup, there's some kind of bug which affects SHM use by the X server on >>> 64bit. >>> I am looking into it. >>> >>> You can also work around this by starting the X server with '-extension >>> MIT-SHM' >> >> After going around in circles on this a few times, this is what I now think I >> know: >> >> The proximate cause of this error is that the x86_64 libcairo2 package >> appears >> to be built with IPC_RMID_DEFERRED_RELEASE defined, which should only happen >> on systems which allow processes to shmat() to a shared memory segment which >> has already been marked for deletion with shmctl(IPC_RMID) (A non-portable >> Linux behaviour) >> >> (This behaviour can be turned on in cygwin by setting the >> 'kern.ipc.shm_allow_removed' to 'yes' in /etc/cygserver.conf, so that is also >> a work around) >> >> Attached is the configure test extracted from cairo, which for some reason >> functions incorrectly on x86_64. >> >>> $ uname -a >>> CYGWIN_NT-5.1 byron 1.7.20(0.266/5/3) 2013-06-07 11:11 i686 Cygwin >>> >>> $ ./shmtest ; echo $? >>> 1 >> >>> $ uname -a >>> CYGWIN_NT-6.1 allegra 1.7.21(0.267/5/3) 2013-07-15 13:50 x86_64 Cygwin >>> >>> $ ./shmtest ; echo $? >>> 0
Sorry, I obviously didn't explain the issue very clearly here, as there has been some confusion. > You tested cygwin-1.7.20 on x86 but cygwin-1.7.21 on x86_64. I'm getting a > return value of 0 with cygwin-1.7.21 on both x86 and x86_64. But I have to > have cygserver running in the x86_64 case; otherwise I get "Bad system call > (core dumped)" and a return value of 140. Unless 'kern.ipc.shm_allow_removed' is set to 'yes', it is a bug in cygwin if this test returns 0. Such a bug definitely exists on x86_64. > Did you have cygserver running when you did your tests? It doesn't seem good > that the outcome of a configure test should depend on whether or not the > person building the package happens to have cygserver running while doing the > build. Running this test when cygserver isn't running is safe. Testing if the shared memory implementation has IPC_RMID_DEFERRED_RELEASE comes to the safe conclusion that it doesn't, if shared memory isn't unavailable. I agree that this configure test is slightly dangerous, but for different reasons: if the test returns 0 (which should only happen if cygserver is running, AND it is configured with 'kern.ipc.shm_allow_removed yes') then the built libcairo will not work reliably on a system which has cygserver running, but 'kern.ipc.shm_allow_removed no' (the default). (That is, the test is written assuming that IPC_RMID_DEFERRED_RELEASE is fixed property of a target) The built cairo will work reliably on a system which doesn't have cygserver running, or has an X server which as been started with '-extension MIT-SHM' to disable use of shared memory, or is running on a different system from the X server, as cairo contains fallbacks for the case when shared memory with the X server is not available...
