Date: Fri, 22 Jun 2001 22:20:01 +0100 From: j mckitrick <jcm@FreeBSD-uk.eu.org> To: Terry Lambert <tlambert@primenet.com> Cc: Michael Lucas <mwlucas@blackhelicopters.org>, Dag-Erling Smorgrav <des@ofug.org>, freebsd-chat@FreeBSD.ORG Subject: Re: most complex code in BSD? Message-ID: <20010622222000.C64495@dogma.freebsd-uk.eu.org> In-Reply-To: <200106222114.OAA28441@usr06.primenet.com>; from tlambert@primenet.com on Fri, Jun 22, 2001 at 09:14:56PM %2B0000 References: <20010622062238.A45123@blackhelicopters.org> <200106222114.OAA28441@usr06.primenet.com>
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I found this in a link given to me by mike meyer. It's from Ritchie's
webpage:
retu(rp->p_addr);
sureg();
/*
* If the new process paused because it was
* swapped out, set the stack level to the last call
* to savu(u_ssav). This means that the return
* which is executed immediately after the call to aretu
* actually returns from the last routine which did
* the savu.
*
* You are not expected to understand this.
*/
if(rp->p_flag&SSWAP) {
rp->p_flag =& ~SSWAP;
aretu(u.u_ssav);
}
/*
* The value returned here has many subtle implications.
* See the newproc comments.
*/
return(1);
So we tried to explain what was going on. "You are not expected to
understand this" was intended as a remark in the spirit of "This won't
be on the exam," rather than as an impudent challenge.
| That's the startup code following relocation, where they push
| a return address value on the stack, and then return to start
| running on a different stack.
|
| In FreeBSD, this is in /sys/i386/i386/locore.s:
|
| -------------------------------------------------------------------------
| /* Now enable paging */
| movl R(_IdlePTD), %eax
| movl %eax,%cr3 /* load ptd addr into mmu */
| movl %cr0,%eax /* get control word */
| orl $CR0_PE|CR0_PG,%eax /* enable paging */
| movl %eax,%cr0 /* and let's page NOW! */
|
| #ifdef BDE_DEBUGGER
| /*
| * Complete the adjustments for paging so that we can keep tracing through
| * initi386() after the low (physical) addresses for the gdt and idt become
| * invalid.
| */
| call bdb_commit_paging
| #endif
|
| pushl $begin /* jump to high virtualized address */
| ret
|
| -------------------------------------------------------------------------
|
| It's not that hard to understand, since it's in assembly language;
| the original stack-SPAM from C was much, much dirtier, and ended up
| being non-portable.
|
| -- Terry
Jonathon
--
Microsoft complaining about the source license used by
Linux is like the event horizon calling the kettle black.
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