linux-kernel - a problem in cpucheck.c on x86

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Message-ID: <CAOvLkw08BQjexftPZbKCL83uuSaAS7Cn2q2rAamewDDbVtPcxw@mail.gmail.com>
Date:	Thu, 15 Dec 2011 15:51:44 +0800
From:	ttlxzz ccc <boyzccc@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: a problem in cpucheck.c on x86

Hi,all:

In arch/x86/boot/cpucheck.c
static int has_eflag(u32 mask)
{
	u32 f0, f1;

	asm("pushfl ; "
	    "pushfl ; "
	    "popl %0 ; "
	    "movl %0,%1 ; "
	    "xorl %2,%1 ; "
	    "pushl %1 ; "
	    "popfl ; "
	    "pushfl ; "
	    "popl %1 ; "
	    "popfl"
	    : "=&r" (f0), "=&r" (f1)
	    : "ri" (mask));

	return !!((f0^f1) & mask);
}

	    "pushl %1 ; "
	    "popfl ; "
	    "pushfl ; "
	    "popl %1 ; "
I don't know what does above 4 instructions do, and I rewirte it like this:

static int has_eflag(u32 mask)
{
        u32 f0;

        asm("pushfl ; "
            "pushfl ; "
            "popl %0 ; "
            "popfl"
            : "=&r" (f0));

        return ~f0 & mask;

}
It works well, and I just want to know is there some special meanings
of the 4 instructions?
	    "pushl %1 ; "
	    "popfl ; "
	    "pushfl ; "
	    "popl %1 ; "
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