mingw-w64-crt/intrincs/readfsdword.c

#include <intrin.h>

/* for x86 only */
unsigned long __readfsdword(unsigned long Offset)
{
   unsigned long ret;
   __asm__ volatile ("movl	%%fs:%1,%0"
     : "=r" (ret) ,"=m" ((*(volatile long *) Offset)));
   return ret;
}