mingw-w64-crt/intrincs/writefsword.c

#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif
#define __CRT__NO_INLINE
#include <windows.h>

/* for x86 only */
 VOID __writefsword(DWORD Offset,WORD Data);

 VOID __writefsword(DWORD Offset,WORD Data)
 {
    __asm__ volatile ("movw	%0,%%fs:%1"
      : "=r" (Data) ,"=m" ((*(volatile long *) Offset)));
 }