Strange segmentation fault with threads / xlib

I wrote this small program (Yes I know, that is stupid, horrible and useless, but everybody has to learn :-) :

#include <stdio.h>
#include <pthread.h>
#include <X11/Xlib.h>

#define DisplayName NULL
#define DefaultWindowWidth 640
#define DefaultWindowHeight 480

Display *XDisplay;

Window MainWindow;
GC GraphicsContext;
int Border,Background;

static int quit_handler() {
printf("Window closed manually ! Program terminated..\n");
}

static void XMain(void *parm) {
XEvent Event;
int Quit;
Quit = 0;
XSelectInput(XDisplay, MainWindow, ExposureMask | StructureNotifyMask
| ButtonPressMask);
XDrawLine(XDisplay,MainWindow, GraphicsContext, 0, 0,
DefaultWindowWidth,DefaultWindowHeight);
for(;;) {
XNextEvent(XDisplay, &Event);
switch (Event.type) {
case ButtonPress:

     printf("Bouton %i ! (%i ; %i)
\n",Event.xbutton.button,Event.xbutton.x,
        Event.xbutton.y);
     break;
   case Expose:
     XDrawLine(XDisplay,MainWindow, GraphicsContext, 0, 0,
DefaultWindowWidth,DefaultWindowHeight);
     break;

}
if (Quit) break;
XFlush(XDisplay);
}
}

int main(int argc, char *argv[]) {

pthread_t EventThread;
pthread_attr_t *EventThreadAttr;

XEvent
Event;

/* Here is the problem (!) */

XInitThreads();
XSetIOErrorHandler(quit_handler);
XDisplay = XOpenDisplay(DisplayName);
if (XDisplay==0) {
printf("XOpenDisplay : Error ; exiting 1.\n");
exit(1);
} else {

printf("XOpenDisplay : Success.\n");
}

Border = BlackPixel(XDisplay, XDefaultScreen(XDisplay)); Background = WhitePixel(XDisplay, XDefaultScreen(XDisplay));

MainWindow =
XCreateSimpleWindow(XDisplay,XRootWindow(XDisplay,XDefaultScreen(XDisplay)),

20,20,DefaultWindowWidth,DefaultWindowHeight,2,Border,Background);
if (MainWindow==0) {
printf("XCreateSimpleWindow : Error ; exiting 1.\n");
} else {
printf("XCreateSimpleWindow : Success.\n");
}

XMapWindow(XDisplay,MainWindow); GraphicsContext = XCreateGC(XDisplay,MainWindow,0,NULL); XSetForeground(XDisplay, GraphicsContext, Border); XFlush(XDisplay);

pthread_attr_init(EventThreadAttr);
if (pthread_create(&EventThread,EventThreadAttr,(void*)XMain,NULL) != 0) {
printf("Error Creating XMain thread ! Exiting 1.\n"); exit(1);
}
while(1) {
}
}

Which I compile using the following commandline :
gcc xlibtest.c -o xlibtest -L/usr/X11R6/lib -lpthread -lX11

_This_ DOES work. The program is acting exactly as expected. But you may have noticed the useless declaration "XEvent Event;" at the beginning of main(). I tried to remove it, and the program crashes with "Segmentation fault." Yes, simply by removing a useless local scope variable declaration. I can't use gdb because then the program receives SIGSEGV all times. It looks like it's not very good at debugging threaded programs.

I'm using :

- GCC 3.3.2
Configured with: ../gcc-3.3.2/configure --prefix=/usr --enable-shared --enable-threads=posix --enable-__cxa_atexit --disable-checking --with-gnu-ld --verbose --target=i486-slackware-linux --host=i486-slackware-linux

- LD 2.14.90.0.7 20031029 (Sounds like a CVS snapshot ? Probably, I upgraded it with the development version of my distro. Could it be the problem ?)
- Linux 2.6.0-test9 (Yes, again a test-version :-/ Am simply fond of it.)

May anyone have a look, and tell me where is the problem in my code, or if there is a need to make a bug report ?