$ gdb --pid=5152
GNU gdb (GDB) 7.3.50.20111026-cvs (cygwin-special)
[...]
Reading symbols from /usr/bin/XWin.exe...Reading symbols from /usr/lib/debug/usr/bin/XWin.dbg...
warning: section .gnu_debuglink not found in /usr/lib/debug/usr/bin/XWin.dbg
done.
done.
(gdb) c
Continuing.

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 6040.0x1ac]
0x004097c2 in NetWMToWinIconAlpha (icon=0xfed20010)
    at /opt/wip/cygport-git/xorg-server/xorg-server-1.12.0-1/src/xserver-cygwin-1.12.0-1/hw/xwin/winmultiwindowicons.c:295
295     /opt/wip/cygport-git/xorg-server/xorg-server-1.12.0-1/src/xserver-cygwin-1.12.0-1/hw/xwin/winmultiwindowicons.c: No such file or directory.
        in /opt/wip/cygport-git/xorg-server/xorg-server-1.12.0-1/src/xserver-cygwin-1.12.0-1/hw/xwin/winmultiwindowicons.c
(gdb) bt full
#0  0x004097c2 in NetWMToWinIconAlpha (icon=0xfed20010)
    at /opt/wip/cygport-git/xorg-server/xorg-server-1.12.0-1/src/xserver-cygwin-1.12.0-1/hw/xwin/winmultiwindowicons.c:295
        hdc = <optimized out>
        ii = {fIcon = 1, xHotspot = 0, yHotspot = 0, hbmMask = 0xf050f17,
          hbmColor = 0x93051250}
        bmh = {bV4Size = 108, bV4Width = 512, bV4Height = -512, bV4Planes = 1,
          bV4BitCount = 32, bV4V4Compression = 3, bV4SizeImage = 0,
          bV4XPelsPerMeter = 0, bV4YPelsPerMeter = 0, bV4ClrUsed = 0,
          bV4ClrImportant = 0, bV4RedMask = 16711680, bV4GreenMask = 65280,
          bV4BlueMask = 255, bV4AlphaMask = 4278190080, bV4CSType = 0,
          bV4Endpoints = {ciexyzRed = {ciexyzX = 0, ciexyzY = 0, ciexyzZ = 0},
            ciexyzGreen = {ciexyzX = 0, ciexyzY = 0, ciexyzZ = 0},
            ciexyzBlue = {ciexyzX = 0, ciexyzY = 0, ciexyzZ = 0}},
          bV4GammaRed = 0, bV4GammaGreen = 0, bV4GammaBlue = 0}
        width = <optimized out>
        height = 512
        pixels = 0xfed20018
        result = 0x2610b75
        DIB_pixels = 0x4ff0000
#1  NetWMToWinIcon (bpp=<optimized out>, icon=0xfed20010)
    at /opt/wip/cygport-git/xorg-server/xorg-server-1.12.0-1/src/xserver-cygwin-1.12.0-1/hw/xwin/winmultiwindowicons.c:369
        hasIconAlphaChannel = 1
        versionChecked = 1 '\001'
#2  0x0040a085 in winXIconToHICON (pWin=0x805399d8, iconSize=32)
    at /opt/wip/cygport-git/xorg-server/xorg-server-1.12.0-1/src/xserver-cygwin-1.12.0-1/hw/xwin/winmultiwindowicons.c:449
        mask = <optimized out>
        image = <optimized out>
        imageMask = <optimized out>
        dst = <optimized out>
        src = <optimized out>
        iconPtr = <optimized out>
        maskPtr = <optimized out>
        planes = 1
        bpp = 32
        effBPP = <optimized out>
        i = <optimized out>
        biggest_size = 512
        hDC = <optimized out>
        ii = {fIcon = 1969585604, xHotspot = 1969585555, yHotspot = 283154527,
          hbmMask = 0x0, hbmColor = 0x0}
        hints = {flags = 1969585433, input = 11, initial_state = 11,
          icon_pixmap = 0, icon_window = 4292791408, icon_x = 1969578512,
          icon_y = -2142004644, icon_mask = 1024, window_group = 4292791464}
        hIcon = 0x0
        biggest_icon = <optimized out>
        _XA_NET_WM_ICON = 361
        generation = 1
        icon = <optimized out>
        icon_data = <optimized out>
        size = <optimized out>
#3  0x0040a5be in winUpdateIcon (id=10487015)
    at /opt/wip/cygport-git/xorg-server/xorg-server-1.12.0-1/src/xserver-cygwin-1.12.0-1/hw/xwin/winmultiwindowicons.c:545
        pWinPriv = 0x80539a5c
        pWin = 0x805399d8
        hIcon = 0x0
        hIconSmall = 0x0
        hIconOld = <optimized out>
#4  0x004204b0 in winMultiWindowWMProc (pArg=0x8003f878)
    at /opt/wip/cygport-git/xorg-server/xorg-server-1.12.0-1/src/xserver-cygwin-1.12.0-1/hw/xwin/winmultiwindowwm.c:809
        pNode = 0x805398e0
        __cleanup_handler = {function = 0x41ec30 <winMultiWindowThreadExit>,
          arg = 0x0, next = 0x0}
        pProcArg = 0x8003f878
        pWMInfo = 0x8003ed40
#5  0x610fb6f2 in pthread::thread_init_wrapper(void*) ()
   from /usr/bin/cygwin1.dll
No symbol table info available.
#6  0x61086562 in thread_wrapper(void*) () from /usr/bin/cygwin1.dll
No symbol table info available.
Backtrace stopped: Not enough registers or memory available to unwind further