backtrace by apport-retrace

crash buntu:/var/crash# apport-retrace --stdout /var/crash/_usr_lib_xorg_Xorg.0.c
gpgv: Signature made Tue 01 Nov 2016 04:15:19 PM CST using RSA key ID A88984DC
gpgv: Can't check signature: public key not found
dpkg-source: warning: failed to verify signature on ./xorg-server_1.18.4-0ubuntu0.2.dsc
dpkg-source: info: extracting xorg-server in xorg-server-1.18.4
dpkg-source: info: unpacking xorg-server_1.18.4.orig.tar.gz
dpkg-source: info: applying xorg-server_1.18.4-0ubuntu0.2.diff.gz
dpkg-source: info: upstream files that have been modified: 
 xorg-server-1.18.4/.dir-locals.el
 xorg-server-1.18.4/ChangeLog
 xorg-server-1.18.4/config/dbus-api
 xorg-server-1.18.4/damageext/damageext.h
 xorg-server-1.18.4/doc/c-extensions
 xorg-server-1.18.4/dri3/dri3int.h
 xorg-server-1.18.4/fix-miregion
 xorg-server-1.18.4/fix-miregion-private
 xorg-server-1.18.4/fix-patch-whitespace
 xorg-server-1.18.4/fix-region
 xorg-server-1.18.4/hw/kdrive/Xkdrive.man
 xorg-server-1.18.4/hw/kdrive/fbdev/Xfbdev.man
 xorg-server-1.18.4/hw/xfree86/os-support/shared/platform_noop.c
 xorg-server-1.18.4/hw/xquartz/GL/glcontextmodes.c
 xorg-server-1.18.4/hw/xquartz/GL/glcontextmodes.h
 xorg-server-1.18.4/hw/xwin/winclipboard/internal.h
 xorg-server-1.18.4/xkb/XKM_file_format.txt
W: Can't drop privileges for downloading as file 'xorg-server_1.18.4-0ubuntu0.2.dsc' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
--- stack trace ---
#0  0x0000ffff9220b528 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
        _sys_result = 0
        pd = 0xffff91fa7000
        pid = 7478
        selftid = 7478
#1  0x0000ffff9220c9e0 in __GI_abort () at abort.c:89
        save_stage = 2
        act = {__sigaction_handler = {sa_handler = 0xa6530de400000000, sa_sigaction = 0xa6530de400000000}, sa_mask = {__val = {2676586395008836901, 2676586395008836901, 2594, 6730122966621824347, 32, 2910292295676945778, 18446744073709486080, 0, 18446744073709551360, 0, 4616194021471027200, 1024, 4616194021471028224, 0, 4616194021471028225, 4616194021471028225}}, sa_flags = -1054354032, sa_restorer = 0xaaaac122fa28 <System>}
        sigs = {__val = {32, 0 <repeats 15 times>}}
#2  0x0000aaaac122fa28 in OsAbort () at ../../os/utils.c:1408
No locals.
#3  0x0000aaaac1116364 in ddxGiveUp (error=error@entry=EXIT_ERR_ABORT) at ../../../../hw/xfree86/common/xf86Init.c:1102
        i = <optimized out>
#4  0x0000aaaac111643c in AbortDDX (error=error@entry=EXIT_ERR_ABORT) at ../../../../hw/xfree86/common/xf86Init.c:1146
        i = <optimized out>
#5  0x0000aaaac12358e0 in AbortServer () at ../../os/log.c:874
No locals.
#6  0x0000aaaac1236624 in FatalError (f=f@entry=0xaaaac1266988 "Caught signal %d (%s). Server aborting\n") at ../../os/log.c:1015
        args = {__stack = 0xffffd085b680, __gr_top = 0xffffd085b680, __vr_top = 0xffffd085b640, __gr_offs = -56, __vr_offs = -128}
        args2 = {__stack = 0xffffd085b680, __gr_top = 0xffffd085b680, __vr_top = 0xffffd085b640, __gr_offs = -56, __vr_offs = -128}
        beenhere = 1
#7  0x0000aaaac122d294 in OsSigHandler (signo=11, sip=0xffffd085b6a0, unused=<optimized out>) at ../../os/osinit.c:150
        unused = <optimized out>
        sip = 0xffffd085b6a0
        signo = 11
#8  <signal handler called>
No symbol table info available.
#9  0x0000aaaac1192254 in RRSetChanged (pScreen=<optimized out>) at ../../randr/randr.c:562
        master = <optimized out>
        mastersp = 0x0
#10 0x0000aaaac119654c in RRScreenSetSizeRange (pScreen=pScreen@entry=0xaaab00cd7860, minWidth=<optimized out>, minHeight=<optimized out>, maxWidth=<optimized out>, maxHeight=<optimized out>) at ../../randr/rrinfo.c:228
No locals.
#11 0x0000aaaac11510d4 in xf86RandR12CreateScreenResources12 (pScreen=0xaaab00cd7860) at ../../../../hw/xfree86/modes/xf86RandR12.c:1649
        c = <optimized out>
        pScrn = <optimized out>
        config = 0xaaab00d02f50
#12 xf86RandR12CreateScreenResources (pScreen=pScreen@entry=0xaaab00cd7860) at ../../../../hw/xfree86/modes/xf86RandR12.c:833
        pScrn = 0xaaab00cd0fd0
        config = <optimized out>
        c = <optimized out>
        width = <optimized out>
        height = <optimized out>
        mmWidth = <optimized out>
        mmHeight = <optimized out>
#13 0x0000aaaac1144bbc in xf86CrtcCreateScreenResources (screen=0xaaab00cd7860) at ../../../../hw/xfree86/modes/xf86Crtc.c:719
        screen = 0xaaab00cd7860
        scrn = <optimized out>
#14 0x0000aaaac10d5cf0 in dix_main (argc=1, argv=0xffffd085cbb8, envp=<optimized out>) at ../../dix/main.c:215
        pScreen = 0xaaab00cd7860
        i = 0
        alwaysCheckForInput = {0, 1}
#15 0x0000ffff921f98a0 in __libc_start_main (main=0x0, argc=0, argv=0x0, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=<optimized out>) at libc-start.c:291
        self = <optimized out>
        result = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {187650361516128, 0, 0, 0, 0, 0, 0, 0, 0, 0, 281474180172400, 3655814494272476266, 129, 3655814493156378226, 0, 0, 0, 0, 0, 0, 0, 0}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0xaaaac127d120, 0xaaaac10bfce8 <_start+52>}, data = {prev = 0x0, cleanup = 0x0, canceltype = -1054355168}}}
        not_first_call = <optimized out>
#16 0x0000aaaac10bfce8 in _start ()
No symbol table info available.
Backtrace stopped: previous frame identical to this frame (corrupt stack?)
--- source code stack trace ---
#0  0x0000ffff9220b528 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
  [Error: raise.c was not found in source tree]
#1  0x0000ffff9220c9e0 in __GI_abort () at abort.c:89
  [Error: abort.c was not found in source tree]
#2  0x0000aaaac122fa28 in OsAbort () at ../../os/utils.c:1408
  1403: OsAbort(void)
  1404: {
  1405: #ifndef __APPLE__
  1406:     OsBlockSignals();
  1407: #endif
  1408:     abort();
  1409: }
  1410: 
  1411: #if !defined(WIN32)
  1412: /*
  1413:  * "safer" versions of system(3), popen(3) and pclose(3) which give up
#3  0x0000aaaac1116364 in ddxGiveUp (error=error@entry=EXIT_ERR_ABORT) at ../../../../hw/xfree86/common/xf86Init.c:1102
  1097:                  */
  1098:                 xf86VGAarbiterLock(xf86Screens[i]);
  1099:                 (xf86Screens[i]->LeaveVT) (xf86Screens[i]);
  1100:                 xf86VGAarbiterUnlock(xf86Screens[i]);
  1101:             }
  1102:     }
  1103: 
  1104:     xf86AccessLeave();
  1105: 
  1106:     /*
  1107:      * This is needed for an abnormal server exit, since the normal exit stuff
#4  0x0000aaaac111643c in AbortDDX (error=error@entry=EXIT_ERR_ABORT) at ../../../../hw/xfree86/common/xf86Init.c:1146
  1141: {
  1142:     int save = xf86LogVerbose;
  1143: 
  1144:     xf86LogVerbose = verb;
  1145:     LogSetParameter(XLOG_FILE_VERBOSITY, verb);
  1146:     return save;
  1147: }
  1148: 
  1149: static void
  1150: xf86PrintDefaultModulePath(void)
  1151: {
#5  0x0000aaaac12358e0 in AbortServer () at ../../os/log.c:874
  869:     XF86BigfontCleanup();
  870: #endif
  871:     CloseWellKnownConnections();
  872:     OsCleanup(TRUE);
  873:     AbortDevices();
  874:     AbortDDX(EXIT_ERR_ABORT);
  875:     fflush(stderr);
  876:     if (CoreDump)
  877:         OsAbort();
  878:     exit(1);
  879: }
#6  0x0000aaaac1236624 in FatalError (f=f@entry=0xaaaac1266988 "Caught signal %d (%s). Server aborting\n") at ../../os/log.c:1015
  1010:     if (!beenhere)
  1011:         OsVendorFatalError(f, args2);
  1012:     va_end(args2);
  1013:     if (!beenhere) {
  1014:         beenhere = TRUE;
  1015:         AbortServer();
  1016:     }
  1017:     else
  1018:         OsAbort();
  1019:  /*NOTREACHED*/}
  1020: 
#7  0x0000aaaac122d294 in OsSigHandler (signo=11, sip=0xffffd085b6a0, unused=<optimized out>) at ../../os/osinit.c:150
  145:             ErrorFSigSafe("%s at address %p\n", strsignal(signo), sip->si_addr);
  146:         }
  147:     }
  148: #endif
  149: 
  150:     FatalError("Caught signal %d (%s). Server aborting\n",
  151:                signo, strsignal(signo));
  152: }
  153: #endif /* !WIN32 || __CYGWIN__ */
  154: 
  155: #include "busfault.h"
#8  <signal handler called>
#9  0x0000aaaac1192254 in RRSetChanged (pScreen=<optimized out>) at ../../randr/randr.c:562
  557:     else {
  558:         master = pScreen;
  559:         mastersp = pScrPriv;
  560:     }
  561: 
  562:     mastersp->changed = TRUE;
  563: }
  564: 
  565: /*
  566:  * Something changed; send events and adjust pointer position
  567:  */
#10 0x0000aaaac119654c in RRScreenSetSizeRange (pScreen=pScreen@entry=0xaaab00cd7860, minWidth=<optimized out>, minHeight=<optimized out>, maxWidth=<optimized out>, maxHeight=<optimized out>) at ../../randr/rrinfo.c:228
  223: 
  224:     pScrPriv->minWidth = minWidth;
  225:     pScrPriv->minHeight = minHeight;
  226:     pScrPriv->maxWidth = maxWidth;
  227:     pScrPriv->maxHeight = maxHeight;
  228:     RRSetChanged(pScreen);
  229:     pScrPriv->configChanged = TRUE;
  230: }
  231: 
  232: #ifdef RANDR_10_INTERFACE
  233: static Bool
#11 0x0000aaaac11510d4 in xf86RandR12CreateScreenResources12 (pScreen=0xaaab00cd7860) at ../../../../hw/xfree86/modes/xf86RandR12.c:1649
  1644: /*
  1645:  * Something happened within the screen configuration due
  1646:  * to DGA, VidMode or hot key. Tell RandR
  1647:  */
  1648: 
  1649: void
  1650: xf86RandR12TellChanged(ScreenPtr pScreen)
  1651: {
  1652:     ScrnInfoPtr pScrn = xf86ScreenToScrn(pScreen);
  1653:     xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(pScrn);
  1654:     int c;
#12 xf86RandR12CreateScreenResources (pScreen=pScreen@entry=0xaaab00cd7860) at ../../../../hw/xfree86/modes/xf86RandR12.c:833
  828:         randrp->virtualX = pScrn->virtualX;
  829:         randrp->virtualY = pScrn->virtualY;
  830:     }
  831:     xf86CrtcSetScreenSubpixelOrder(pScreen);
  832: #if RANDR_12_INTERFACE
  833:     if (xf86RandR12CreateScreenResources12(pScreen))
  834:         return TRUE;
  835: #endif
  836:     return TRUE;
  837: }
  838: 
#13 0x0000aaaac1144bbc in xf86CrtcCreateScreenResources (screen=0xaaab00cd7860) at ../../../../hw/xfree86/modes/xf86Crtc.c:719
  714:     screen->CreateScreenResources = config->CreateScreenResources;
  715: 
  716:     if (!(*screen->CreateScreenResources) (screen))
  717:         return FALSE;
  718: 
  719:     if (!xf86RandR12CreateScreenResources(screen))
  720:         return FALSE;
  721: 
  722:     return TRUE;
  723: }
  724: 
#14 0x0000aaaac10d5cf0 in dix_main (argc=1, argv=0xffffd085cbb8, envp=<optimized out>) at ../../dix/main.c:215
  210:         for (i = 0; i < screenInfo.numGPUScreens; i++) {
  211:             ScreenPtr pScreen = screenInfo.gpuscreens[i];
  212:             if (!CreateScratchPixmapsForScreen(pScreen))
  213:                 FatalError("failed to create scratch pixmaps");
  214:             if (pScreen->CreateScreenResources &&
  215:                 !(*pScreen->CreateScreenResources) (pScreen))
  216:                 FatalError("failed to create screen resources");
  217:         }
  218: 
  219:         for (i = 0; i < screenInfo.numScreens; i++) {
  220:             ScreenPtr pScreen = screenInfo.screens[i];
#15 0x0000ffff921f98a0 in __libc_start_main (main=0x0, argc=0, argv=0x0, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=<optimized out>) at libc-start.c:291
  [Error: libc-start.c was not found in source tree]
#16 0x0000aaaac10bfce8 in _start ()

root@ubuntu:/var/crash#