xcb_writev: Segmentation fault

Thu Aug 31 14:54:44 UTC 2017

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".
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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