How to check Objective-C 2.0 ARC in gnustep linux - automatic-ref-counting

Question

I wanna check ARC write back in linux gnustep environment (I prepared that by this article).
I have main.m file:
#import <Foundation/Foundation.h>
__weak id obWeak;
int writeBack(id *);
int main(int argc, char * argv[]) {
#autoreleasepool {
id object;
writeBack(&object);
NSLog(#"object(%#) weak(%#)", object, obWeak);
object=nil;
NSLog(#"object(%#) weak(%#)", object, obWeak);
}
NSLog(#"weak %#", obWeak);
return 0;
}
int writeBack(id * aValue){
*aValue=[NSObject new];
obWeak = *aValue;
return 0;
}
GNUmakefile:
include $(GNUSTEP_MAKEFILES)/common.make
CC=clang
TOOL_NAME = CmdTest
${TOOL_NAME}_OBJCFLAGS = -fobjc-arc
${TOOL_NAME}_BUNDLE_LIBS += -lobjc -lgnustep-base
${TOOL_NAME}_OBJC_FILES = main.m
include $(GNUSTEP_MAKEFILES)/tool.make
and Linux console output:
2013-03-28 13:50:33.840 CmdTest[7751] object(<NSObject: 0x2068c38>) weak(<NSObject: 0x2068c38>)
2013-03-28 13:50:33.842 CmdTest[7751] object((null)) weak(<NSObject: 0x2068c38>)
Segmentation fault (core dumped)
As you can see, I got Segmentation fault (core dumped) when I tried to call NSLog(#"weak %#", obWeak) from outside of #autoreleasepool block.
I've tried to compile this code at XCode on mac pc and didn't get any error. Could you help me to understand what's wrong with it?