xcb_writev: Segmentation fault

Fri Sep 1 18:01:18 UTC 2017

OK, I found how to fix the problem: I need to use the '-O1' gcc optimization flag instead of '-O2' when building libxcb.
Well, in fact, it is just a workaround and not a fix because I prefer the '-O2' optimization flag but unfortunately I can't use it for building libxcb.
Thanks to Ilya Lipnitskiy (lipnitsk) for this idea: https://bugs.archlinux.org/task/49560

On Thu, 31 Aug 2017 16:54:44 +0200
YuGiOhJCJ Mailing-List <yugiohjcj-mailinglist at laposte.net> wrote:

> Hello,
> 
> I built libX11 1.6.5 32-bit on my 64-bit machine and I try to run a 32-bit application:
> ---
> $ gdb 25Assist
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> Reading symbols from 25Assist...(no debugging symbols found)...done.
> (gdb) run
> Starting program: /opt/25assist-20151223/25Assist 
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib64/libthread_db.so.1".
> warning: File "/usr/lib/libstdc++.so.6.0.23-gdb.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
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> 	add-auto-load-safe-path /usr/lib/libstdc++.so.6.0.23-gdb.py
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> "Auto-loading safe path" section in the GDB manual.  E.g., run from the shell:
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> 
> Program received signal SIGSEGV, Segmentation fault.
> 0xf6f1d6e1 in xcb_writev (c=0x82cbd50, vector=0xffff9e0c, count=3, requests=73) at xcb_out.c:405
> 405	    c->out.request += requests;
> (gdb) bt
> #0  0xf6f1d6e1 in xcb_writev (c=0x82cbd50, vector=0xffff9e0c, count=3, requests=73) at xcb_out.c:405
> #1  0xf767f85e in _XSend (dpy=0x82cb400, data=0x0, size=0) at xcb_io.c:486
> #2  0xf767fe19 in _XReply (dpy=0x82cb400, rep=0xffff9ec4, extra=0, discard=1) at xcb_io.c:573
> #3  0xf767b943 in XSync (dpy=0x82cb400, discard=0) at Sync.c:44
> #4  0xf7a537b2 in IA__gdk_flush () at gdkevents-x11.c:2606
> #5  0xf7a23170 in alloc_scratch_image (image_info=<optimized out>) at gdkimage.c:527
> #6  _gdk_image_get_scratch (screen=0x82da0b8, width=160, height=23, depth=24, x=0xffff9fbc, y=0xffff9fc0) at gdkimage.c:592
> #7  0xf7a30fbe in gdk_draw_rgb_image_core (image_info=0x83f3bf8, drawable=drawable at entry=0x82c6c00, gc=gc at entry=0x82d8e80, x=0, y=0, width=160, height=23, 
>     buf=0x840bc48 "\371\371\371nnn\022\022\022", pixstride=3, rowstride=480, conv=0xf7a2f0a0 <gdk_rgb_convert_0888>, cmap=0x0, xdith=0, ydith=0) at gdkrgb.c:3327
> #8  0xf7a329e9 in IA__gdk_draw_rgb_image (drawable=0x82c6c00, gc=0x82d8e80, x=0, y=0, width=160, height=23, dith=GDK_RGB_DITHER_MAX, rgb_buf=0x840bc48 "\371\371\371nnn\022\022\022", 
>     rowstride=480) at gdkrgb.c:3393
> #9  0x0809d97e in ?? ()
> #10 0x081124a0 in ?? ()
> #11 0x081124d5 in ?? ()
> #12 0xf6252292 in ?? ()
> #13 0xf60cf138 in ?? ()
> #14 0xf60cf3a3 in ?? ()
> #15 0xf62d3f00 in ?? ()
> #16 0xf62ceb8b in ?? ()
> #17 0x0807077d in ?? ()
> #18 0x08070888 in ?? ()
> #19 0x08179267 in ?? ()
> #20 0xf6100128 in ?? ()
> #21 0x0816d65a in ?? ()
> #22 0x0816d64e in ?? ()
> #23 0x0816d75f in ?? ()
> #24 0xf668681b in ?? ()
> #25 0xf60b5308 in ?? ()
> #26 0xf60b53b4 in ?? ()
> #27 0xf6255333 in ?? ()
> #28 0xf60b5469 in ?? ()
> #29 0xf60b5024 in ?? ()
> #30 0x080d2592 in ?? ()
> #31 0x0816c1b1 in ?? ()
> #32 0xf72be4d3 in __libc_start_main () from /lib/libc.so.6
> #33 0x08052b21 in ?? ()
> (gdb) quit
> A debugging session is active.
> 
> 	Inferior 1 [process 18645] will be killed.
> 
> Quit anyway? (y or n) y
> ---
> 
> As you can see I get a segmentation fault after the call to the xcb_writev function.
> From this program stack, I am unable to guess what could be the problem.
> Maybe a communication problem between libX11 and libxcb but why?
> I was able to run this application in the past so I think I did something wrong when I built my 32-bit libX11 this time.
> 
> Can you guess where the problem is from this backtrace?
> 
> Thank you.
> Best regards.
> 
> Remark: I rebuilt gtk+2, libX11 and libxcb with the '-g' flag to have a nice backtrace so that's why you see the debugging symbols.
> 
> 32-bit programs used:
> atk-2.20.0
> cairo-1.14.10
> expat-2.1.0
> fontconfig-2.12.1
> freetype-2.6.3
> gdk-pixbuf2-2.36.6
> glib2-2.52.3
> glibc-2.23
> gtk+2-2.24.30
> harfbuzz-1.2.7
> icu4c-56.1
> libdrm-2.4.80
> libffi-3.2.1
> libjpeg-turbo-1.5.0
> libpciaccess-0.13.5
> libpng-1.6.25
> libtiff-4.0.6
> libX11-1.6.5
> libXau-1.0.8
> libxcb-1.12
> libXcomposite-0.4.4
> libXcursor-1.1.14
> libXdamage-1.1.4
> libXext-1.3.3
> libXfixes-5.0.3
> libXft-2.3.2
> libXi-1.7.9
> libXinerama-1.1.3
> libXrandr-1.5.1
> libXrender-0.9.10
> libxshmfence-1.2
> libXxf86vm-1.1.4
> llvm-3.9.0
> mesa-17.0.4
> ncurses-5.9
> pango-1.40.6
> pcre-8.39
> pixman-0.34.0
> util-linux-2.27.1
> zlib-1.2.8
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