(gdb) run
Starting program: /usr/local/bin/gst-launch-0.10 ximagesrc show-pointer=true \! fakesink
[Thread debugging using libthread_db enabled]
Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Setting pipeline to PLAYING ...
New clock: GstSystemClock

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1215890512 (LWP 26073)]
0xb79cda33 in gst_ximage_src_create (bs=0x0, buf=0x0) at gstximagesrc.c:271
271           color = GUINT32_FROM_LE (*(guint32 *) (dest));
(gdb) print dest
No symbol "dest" in current context.
(gdb) list
266           break;
267         case 16:
268           color = GUINT16_FROM_LE (*(guint32 *) (dest));
269           break;
270         case 32:
271           color = GUINT32_FROM_LE (*(guint32 *) (dest));
272           break;
273         default:
274           /* Should not reach here */
275           g_assert_not_reached ();
(gdb) bt
#0  0xb7a76a33 in gst_ximage_src_create (bs=0x0, buf=0x0) at gstximagesrc.c:271
#1  0xb7a6d5cc in gst_push_src_create (bsrc=0x0, offset=12582912, length=4096, ret=0x0) at gstpushsrc.c:117
#2  0xb7a62f64 in gst_base_src_get_range (src=0x810c020, offset=12582912, length=4096, buf=0xb7918364) at gstbasesrc.c:1304
#3  0xb7a63f2b in gst_base_src_loop (pad=0x810d858) at gstbasesrc.c:1473
#4  0xb7f8065d in gst_task_func (task=0x811fc10, tclass=0x807f610) at gsttask.c:193
#5  0xb7e91448 in g_thread_pool_thread_proxy (data=0x807f6a0) at gthreadpool.c:265
#6  0xb7e8f5a2 in g_thread_create_proxy (data=0x811f248) at gthread.c:582
#7  0xb7e43341 in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#8  0xb7dd84ee in clone () from /lib/tls/i686/cmov/libc.so.6

valgrind complains about this:

==26344==
==26344== Thread 3:
==26344== Invalid read of size 4
==26344==    at 0x466FA33: gst_ximage_src_create (gstximagesrc.c:271)
==26344==    by 0x468C5CB: gst_push_src_create (gstpushsrc.c:117)
==26344==    by 0x4681F63: gst_base_src_get_range (gstbasesrc.c:1304)
==26344==    by 0x4682F2A: gst_base_src_loop (gstbasesrc.c:1473)
==26344==    by 0x407565C: gst_task_func (gsttask.c:193)
==26344==    by 0x4144447: ??? (gthreadpool.c:265)
==26344==    by 0x41425A1: ??? (gthread.c:582)
==26344==    by 0x418CC8B: pthread_start_thread (manager.c:310)
==26344==    by 0x4291109: clone (clone.S:119)
==26344==  Address 0x4CED2A0 is 2,336 bytes inside a block of size 2,338 alloc'd
==26344==    at 0x401B422: malloc (vg_replace_malloc.c:149)
==26344==    by 0x46D3136: XFixesGetCursorImage (in /usr/lib/libXfixes.so.3.0.0)
==26344==    by 0x466F097: gst_ximage_src_create (gstximagesrc.c:550)
==26344==    by 0x468C5CB: gst_push_src_create (gstpushsrc.c:117)
==26344==    by 0x4681F63: gst_base_src_get_range (gstbasesrc.c:1304)
==26344==    by 0x4682F2A: gst_base_src_loop (gstbasesrc.c:1473)
==26344==    by 0x407565C: gst_task_func (gsttask.c:193)
==26344==    by 0x4144447: ??? (gthreadpool.c:265)
==26344==    by 0x41425A1: ??? (gthread.c:582)
==26344==    by 0x418CC8B: pthread_start_thread (manager.c:310)
==26344==    by 0x4291109: clone (clone.S:119)
==26344==
==26344== Invalid write of size 4
==26344==    at 0x466FAC6: gst_ximage_src_create (gstximagesrc.c:321)
==26344==    by 0x468C5CB: gst_push_src_create (gstpushsrc.c:117)
==26344==    by 0x4681F63: gst_base_src_get_range (gstbasesrc.c:1304)
==26344==    by 0x4682F2A: gst_base_src_loop (gstbasesrc.c:1473)
==26344==    by 0x407565C: gst_task_func (gsttask.c:193)
==26344==    by 0x4144447: ??? (gthreadpool.c:265)
==26344==    by 0x41425A1: ??? (gthread.c:582)
==26344==    by 0x418CC8B: pthread_start_thread (manager.c:310)
==26344==    by 0x4291109: clone (clone.S:119)
==26344==  Address 0x4CED2A0 is 2,336 bytes inside a block of size 2,338 alloc'd
==26344==    at 0x401B422: malloc (vg_replace_malloc.c:149)
==26344==    by 0x46D3136: XFixesGetCursorImage (in /usr/lib/libXfixes.so.3.0.0)
==26344==    by 0x466F097: gst_ximage_src_create (gstximagesrc.c:550)
==26344==    by 0x468C5CB: gst_push_src_create (gstpushsrc.c:117)
==26344==    by 0x4681F63: gst_base_src_get_range (gstbasesrc.c:1304)
==26344==    by 0x4682F2A: gst_base_src_loop (gstbasesrc.c:1473)
==26344==    by 0x407565C: gst_task_func (gsttask.c:193)
==26344==    by 0x4144447: ??? (gthreadpool.c:265)
==26344==    by 0x41425A1: ??? (gthread.c:582)
==26344==    by 0x418CC8B: pthread_start_thread (manager.c:310)
==26344==    by 0x4291109: clone (clone.S:119)