Date: Mon, 23 Jul 2001 10:47:02 -0600 From: "Weiguang SHI" <weiguang_shi@hotmail.com> To: zzhang@cs.binghamton.edu Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: using syscalls in a module (stack problem ?) Message-ID: <F155Z2K4xDh9vXsFFsA00002adb@hotmail.com>
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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
> >
> >
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> >
>
>
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