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Date: Mon, 23 Jul 2001 13:18:19 -0400 (EDT)
From: Zhihui Zhang <zzhang@cs.binghamton.edu>
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To: Weiguang SHI <weiguang_shi@hotmail.com>
Cc: freebsd-hackers@FreeBSD.ORG
Subject: Re: using syscalls in a module (stack problem ?)
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Make sense.  But there are other things in the UPAGES.

-Zhihui

On Mon, 23 Jul 2001, Weiguang SHI wrote:

> I guess this is it (/usr/src/sys/i386/i386/locore.s):
> 
>     348 /* now running relocated at KERNBASE where the system is linked to 
> run */
>     349 begin:
>     350         /* set up bootstrap stack */
>     351         movl    _proc0paddr,%esp        /* location of in-kernel 
> pages */
>     352         addl    $UPAGES*PAGE_SIZE,%esp  /* bootstrap stack end 
> location */
> 
> where UPAGES is defined as 2 in 
> /usr/src/sys/compile/MYKERNEL/machine/param.h
> 
>     101 #define UPAGES  2               /* pages of u-area */
> 
> Regards,
> Weiguang
> 
> >From: Zhihui Zhang <zzhang@cs.binghamton.edu>
> >To: msmith@freebsd.org, "Eugene L. Vorokov" <vel@bugz.infotecs.ru>
> >CC: freebsd-hackers@FreeBSD.ORG
> >Subject: Re: using syscalls in a module (stack problem ?)
> >Date: Mon, 23 Jul 2001 12:07:47 -0400 (EDT)
> >
> >
> >Just out of curiosity, Linux's kernel stack is one page. Where in the
> >kernel source code that says that we can have two pages instead of one
> >page kernel stack?
> >
> >-Zhihui
> >
> >
> >On Mon, 23 Jul 2001, Eugene L. Vorokov wrote:
> >
> > > > > I call this function with (curproc, PATH_MAX+1), and everything is 
> >fine
> > > > > when I have just a few local variables defined in the caller (it all
> > > > > works on MOD_LOAD only). However, if I have 2 buffers, 4096 bytes 
> >each,
> > > > > as local variables and then try to allocate userspace memory the 
> >same
> > > > > way, kernel crashes - sometimes inside mmap(), sometimes a bit 
> >later.
> > > > >
> > > > > Why could this happen ? Is it related to possible stack overflow ?
> > > >
> > > > Yes.  The kernel stack is only two pages; you absolutely must not use
> > > > large local variables in the kernel.
> > >
> > > I see. But I still can define them using "static", right ?
> > >
> > > Regards,
> > > Eugene
> > >
> > >
> > > To Unsubscribe: send mail to majordomo@FreeBSD.org
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> > >
> >
> >
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> 
> 
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