[Xcb] Re: xcblock.c Assertion

Jamey Sharp jamey at minilop.net
Thu Sep 14 23:10:01 PDT 2006

On Thu, Sep 14, 2006 at 08:53:58PM -0400, Paul Moss wrote:
> I did a git checkout master; ./autogen.sh ; make ; make install
> (this was at about 8:30 PM EDT on 9/14)

Thanks for the timestamps. Nothing significant had changed recently in
either Xlib or XCB before you first reported problems on Monday, though,
so if this is our bug I guess it isn't especially new.

> GNU gdb 6.1.1

Your gdb is two years and four releases old: it's possible that a newer
version will be more helpful.

> This GDB was configured as "i486-slackware-linux"...

You're using Slackware, I take it? I don't know if we've had anyone test
on that distribution before. :-)

> gaim: xcl/xcblock.c:128: _XGetXCBBuffer: Assertion `((int) ((xcb_req)
> - (dpy->request)) >= 0)' failed.
> ...
> #5  0x406ae56c in __assert_fail () from /lib/libc.so.6
> #6  0x407b4ee0 in _IO_2_1_stdout_ () from /lib/libc.so.6
> #7  0xbfcbd591 in ?? ()
> #8  0x407adfe6 in in6addr_loopback () from /lib/libc.so.6
> #9  0x40638771 in xrmtypes () from /usr/X11R7/lib/libX11.so.6
> #10 0x00000080 in ?? ()
> #11 0x406387aa in xrmtypes () from /usr/X11R7/lib/libX11.so.6
> #12 0x407adfe6 in in6addr_loopback () from /lib/libc.so.6
> #13 0x406388e0 in xrmtypes () from /usr/X11R7/lib/libX11.so.6
> #14 0x4000a490 in _dl_map_object_deps () from /lib/ld-linux.so.2
> Previous frame inner to this frame (corrupt stack?)
> Does that help any?

You did the right steps, but the stack trace looks completely bogus
below __assert_fail, and therefore useless. For example,
in6addr_loopback is read-only data, not a function. Can you upgrade gdb,
get a version of libc with debugging symbols, and try again?

Sometimes when debugging these sorts of problems, I've had good look
with studying a trace of the packets. Force the use of TCP: you may have
to remove "-nolisten tcp" from your X server arguments in gdm, kdm, or
whatever. Then start up tcpdump to log the packets:
	sudo tcpdump -w gaim.log -i lo -s 0 tcp portrange 6000-6020
and, while that's running, run one failing application:
	DISPLAY=localhost:0 gaim

Then send me or the list the resulting 'gaim.log', or file a bug report
with the evidence you've got so far -- http://bugs.freedesktop.org/.

I'm either concerned or hopeful that this is some weird interaction
between Xlib and old versions of other software on your system. But I
don't have enough information yet.

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