From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <f7593b21b01e82b1a22a98af06c7b133@terzarima.net>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Re: Threads: Sewing badges of honor onto a Kernel
From: Charles Forsyth <forsyth@terzarima.net>
In-Reply-To: <20040227115257.F22848@cackle.proxima.alt.za>
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Date: Fri, 27 Feb 2004 10:00:32 +0000
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>>Just out of curiosity, how do I get to the private space without
>>a lock?  It's been a long time since I studied these things and lots
>>of water has flown under bridges, so I could be missing something.

static __inline Proc *getup(void) {
	Proc *p;
	__asm__(	"movl	%%esp, %%eax\n\t"
			: "=a" (p)
	);
	return *(Proc **)((unsigned long)p & ~(KSTACK - 1));
};

where the process that makes the new process's stack puts a pointer to
the private space (a Proc* in this case) at the base of that stack, and where KSTACK is
a power-of-2.  i don't think it can be accessed portably in Linux,
but you don't need a lock.