fatal@neologic fatal $ gdb /usr/local/bin/xmms

Invoke the debugger with xmms as the argument, full path is optional if XMMS is in your command path. (no reason why it shouldn't be).

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(gdb) run

Starts the debugging.

Starting program: /usr/local/bin/xmms
[New Thread 16384 (LWP 2397)]
[New Thread 32769 (LWP 2398)]
[New Thread 16386 (LWP 2399)]
[New Thread 32771 (LWP 2401)]
[New Thread 49156 (LWP 2402)]

Do what you need to get XMMS to crash and then return to GDB.

Program received signal SIGSEGV, Segmentation fault.
0x40182653 in gdk_image_get () from /usr/lib/libgdk-1.2.so.0
(gdb) bt

Issue the 'backtrace' (bt) command.

#0  0x40182653 in gdk_image_get () from /usr/lib/libgdk-1.2.so.0
#1  0x08071d88 in playlistslider_draw (w=0x81d9318) at playlist_slider.c:51
#2  0x0806b0c0 in draw_widget_list (wlist=0x81d22a4, redraw=0xbffff764,
    force=0) at widget.c:124
#3  0x080875f4 in draw_playlist_window (force=0) at playlistwin.c:1435
#4  0x0807aff0 in idle_func (data=0x0) at main.c:3059
#5  0x401ae143 in g_timeout_dispatch () from /usr/local/lib/libglib-1.2.so.0
#6  0x401ad37f in g_main_dispatch () from /usr/local/lib/libglib-1.2.so.0
#7  0x401ad92b in g_main_iterate () from /usr/local/lib/libglib-1.2.so.0
#8  0x401adaa9 in g_main_run () from /usr/local/lib/libglib-1.2.so.0
#9  0x400d7e49 in gtk_main () from /usr/lib/libgtk-1.2.so.0
#10 0x0807befd in main (argc=1, argv=0xbffff924) at main.c:3494
#11 0x402d82e7 in __libc_start_main () from /lib/libc.so.6