memory debugger

[Markus Lausser <sgop users sourceforge net>]

I need a memory debugger that works with gtk and that is able to show
invalid memory access (like buffer overflows, access of already freed
memory).

I've already tried electric fence, but it already crashes in gtk_init()
(gdb) bt
#0  gconv (step=0x41218fc8, data=0xbffff140, inbuf=0xbffff134, inbufend=0x40756ffd "", written=0xbffff138, 
    do_flush=0) at ../iconv/skeleton.c:204
#1  0x402e2f17 in __mbrtowc (pwc=0xbffff2fc, s=0x40756ffc "#", n=1, ps=0x40375d88) at mbrtowc.c:67
#2  0x4029e602 in mbtowc (pwc=0xbffff2fc, s=0x40756ffc "#", n=1) at mbtowc.c:59
#3  0x4023f0cb in stdc_mbstowcs () from /usr/X11R6/lib/libX11.so.6
#4  0x40239a48 in _XlcConvert () from /usr/X11R6/lib/libX11.so.6
#5  0x402478eb in _Xlcmbstowcs () from /usr/X11R6/lib/libX11.so.6
#6  0x40247aa3 in _Xmbstowcs () from /usr/X11R6/lib/libX11.so.6
#7  0x402305ae in parseline () from /usr/X11R6/lib/libX11.so.6
#8  0x40230806 in XimParseStringFile () from /usr/X11R6/lib/libX11.so.6
#9  0x4022f537 in _XimCreateDefaultTree () from /usr/X11R6/lib/libX11.so.6
#10 0x4022f5dd in _XimLocalOpenIM () from /usr/X11R6/lib/libX11.so.6
#11 0x4022ec98 in _XimOpenIM () from /usr/X11R6/lib/libX11.so.6
#12 0x4020484a in XOpenIM () from /usr/X11R6/lib/libX11.so.6
#13 0x4016a418 in gdk_im_real_open () at gdkim.c:376
#14 0x4016a52d in gdk_im_open () at gdkim.c:419
#15 0x401594fc in gdk_init_check (argc=0xbffff758, argv=0xbffff75c) at gdk.c:436
#16 0x400b3996 in gtk_init_check (argc=0xbffff758, argv=0xbffff75c) at gtkmain.c:199
#17 0x400b3dcd in gtk_init (argc=0xbffff758, argv=0xbffff75c) at gtkmain.c:423
#18 0x805a6ae in main (argc=1, argv=0xbffff79c) at main.c:32

So, does anyone know any other free memory debugger?