/tmp/ruperts/emacs-build> gdb --args src/emacs -Q --eval '(x-focus-frame (selected-frame))'
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Reading symbols from /tmp/ruperts/emacs-build/src/emacs...done.
(gdb) break data.c:2545
Breakpoint 1 at 0x5493a2: file ../../emacs-source/src/data.c, line 2545.
(gdb) r
Starting program: /tmp/ruperts/emacs-build/src/emacs -Q --eval \(x-focus-frame\ \(selected-frame\)\)
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[New Thread 0x7ffff1a70700 (LWP 13085)]

Breakpoint 1, cons_to_signed (c=<optimized out>, min=-2147483648, max=2147483647) at ../../emacs-source/src/data.c:2545
2545        error ("Not an in-range integer, float, or cons of integers");
(gdb) bt 10
#0  cons_to_signed (c=<optimized out>, min=-2147483648, max=2147483647) at ../../emacs-source/src/data.c:2545
#1  0x00000000004d5471 in x_fill_property_data (dpy=0x1394f70, data=<optimized out>, ret=<optimized out>, format=32) at ../../emacs-source/src/xselect.c:2314
#2  0x00000000004d5886 in x_send_client_event (display=<optimized out>, dest=<optimized out>, from=<optimized out>, message_type=239, format=<optimized out>, 
    values=21641606) at ../../emacs-source/src/xselect.c:2597
#3  0x00000000004d16ad in x_focus_frame (f=0x10bb600) at ../../emacs-source/src/xfns.c:3372
#4  0x000000000041bc41 in Fx_focus_frame (frame=<optimized out>) at ../../emacs-source/src/frame.c:2237
#5  0x000000000055a000 in eval_sub (form=<optimized out>) at ../../emacs-source/src/eval.c:2178
#6  0x000000000055c2c1 in Feval (form=21641542, lexical=<optimized out>) at ../../emacs-source/src/eval.c:1993
#7  0x000000000055abeb in Ffuncall (nargs=<optimized out>, args=<optimized out>) at ../../emacs-source/src/eval.c:2726
#8  0x000000000059066d in exec_byte_code (bytestr=3783118445, vector=-2147483648, maxdepth=2147483647, args_template=1, nargs=2, args=0x7fffffffd690)
    at ../../emacs-source/src/bytecode.c:920
#9  0x000000000055a984 in Ffuncall (nargs=<optimized out>, args=0x7fffffffd688) at ../../emacs-source/src/eval.c:2784
(More stack frames follow...)
(gdb) frame 1
#1  0x00000000004d5471 in x_fill_property_data (dpy=0x1394f70, data=<optimized out>, ret=<optimized out>, format=32) at ../../emacs-source/src/xselect.c:2314
2314                val = cons_to_signed (o, X_LONG_MIN, X_LONG_MAX);
(gdb) l
2309                     The XDnd spec. is not explicit about negative values,
2310                     but let's assume negative v2 is sent modulo 2**16.  */
2311                  val = (v1 << 16) | (v2 & 0xffff);
2312                }
2313              else
2314                val = cons_to_signed (o, X_LONG_MIN, X_LONG_MAX);
2315            }
2316          else if (STRINGP (o))
2317            {
2318              block_input ();
(gdb) p/x o
$1 = 0x385f739b4
(gdb) p/x X_LONG_MIN
$2 = 0x80000000
(gdb) p/x X_LONG_MAX
$3 = 0x7fffffff
(gdb) p/x LONG_MAX
$4 = 0x7fffffffffffffff