From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <3c0fef0da69af9add75dc63c8a82b22e@coraid.com>
From: erik quanstrom <quanstro@coraid.com>
Date: Sat, 17 Mar 2007 14:00:17 -0400
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Alef - run time error
In-Reply-To: <f1857955703a4902e613ed94cc9a8c87@proxima.alt.za>
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On Sat Mar 17 13:23:51 EDT 2007, lucio@proxima.alt.za wrote:
> > the pc address space got bigger in 2005 so that programs could
> > use more than 2gb of memory.  the top of the stack is now
> > 0xdffff000 instead of 0x7ffff000, so if you s/0x7/0xd/ you
> > will probably be okay.
> > 
> Thank you very much, that worked fine, which is OK at least to test
> the compiler.
> 
> >   it would be even better if _main looked
> > at its stack pointer and anded off some bits, so that those
> > weren't hard-coded.
> > 
> If you know a quick way to inspect the stack pointer, rather than me
> having to dig for it, I'll fix it with pleasure.  



this c program will tell you where c leaves the tos.

	#include<u.h>
	#include<libc.h>
	void
	main(void)
	{
		char *tos;
		print("%p\n", &tos);
		exits("");
	}

for me this prints dfffef68. so there are 0x98 bytes taken
from the top of the stack before main starts.


> Alternatively, if
> you know where I ought to look, please point me there.  Oh, yes,
> please also explain what "and"ing off a few bits means, unless you
> mean that by trimming the incoming stack pointer I'll get a reasonable
> value for a private copy.  That would make just about as much sense as
> I can grasp.

i'm pretty sure that's what he's after.  /sys/src/libc/386/main9.s subtracts
a constant from _tos.

- erik