syscall

这里使用了宏展开

#define _syscall0(type,name) \
type name(void) \
{ \
long __res; \
__asm__ volatile ("int $0x80" \
        : "=a" (__res) \
        : "0" (__NR_##name)); \
if (__res >= 0) \
        return (type) __res; \
errno = -__res; \
return -1; \
}

static inline _syscall0(int,fork)


static inline int fork()
{
    long __res;
    __asm__ volatile("int $0x80" : "=a"(__res) : "0"(__NR__fork));
    if(__res >= 0)
        return (int) __res;
    errno = -__res;
    return -1;
}