Kernelnewbies Digest, Vol 22, Issue 1

[kishore kumar]

hello everybody,

I am new to kernel programming.
Can anyone tell me how to start it.

kishore kumar

On Sun, Sep 2, 2012 at 9:30 PM, <kernelnewbies-request at kernelnewbies.org>wrote:

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> Today's Topics:
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>    1. Re: map bss to addr zero (Ritesh Harjani)
>    2. Re: map bss to addr zero (Mulyadi Santosa)
>    3. Re: Kernel booting problem. (Jim Cromie)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 2 Sep 2012 00:53:17 +0530
> From: Ritesh Harjani <ritesh.harjani at gmail.com>
> Subject: Re: map bss to addr zero
> To: Srinivas Ramanan <srinivas.ramanan at gmail.com>,
>         mulyadi.santosa at gmail.com
> Cc: kernelnewbies at kernelnewbies.org
> Message-ID:
>         <
> CAD15agbM8jO+-KmrRByDpd0NRN3k_bcpEQi9p8W721c8_9Pefg at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> On Mon, Aug 27, 2012 at 2:01 AM, Srinivas Ramanan <
> srinivas.ramanan at gmail.com> wrote:
>
> > Hi all,
> > This is an interview question.
> > "What is the implication of mapping BSS to the Virtual Memory Segment 0?"
> >
> >  I was not able to find the answer from web. So posting here.
> > thanks,
> > srinivas
> >
> > _______________________________________________
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> >
>
>
> Hi,
>
> The bss section typically includes all uninitialized variables declared
> with the static keyword.
> The zero page which  is a copy-on-write page that reads as zero is used to
> map the BSS segment. Any process referencing the zero page sees the page
> filled with zeos and if it tries to writes to the page, it ends up
> modifying a private copy. (LDD ch15. page 429)
>
> Mulyadi,
>
> Why it will generate a page fault later when process will tries to
> reference it, while it already has mapped with the zero page?
>
>
> Sorry if i am wrong anywhere.
> Ritesh
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> ------------------------------
>
> Message: 2
> Date: Sun, 2 Sep 2012 12:46:29 +0700
> From: Mulyadi Santosa <mulyadi.santosa at gmail.com>
> Subject: Re: map bss to addr zero
> To: Ritesh Harjani <ritesh.harjani at gmail.com>
> Cc: Srinivas Ramanan <srinivas.ramanan at gmail.com>,
>         kernelnewbies at kernelnewbies.org
> Message-ID:
>         <CAGdaadYXCTYad0aRKME1eyQ-rt1gh=vN=
> Siyz2HtQzONpCBgVw at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi... :)
>
> On Sun, Sep 2, 2012 at 2:23 AM, Ritesh Harjani <ritesh.harjani at gmail.com>
> wrote:
> > Mulyadi,
> >
> > Why it will generate a page fault later when process will tries to
> reference
> > it, while it already has mapped with the zero page?
> >
> >
>
> Hopefully I interpret it correctly that this question is for me :)
>
> Sorry, maybe I am not clear, by reference, I meant "updating " or
> "writing" new value.
>
> Since this zero page is mapped as read only, when writing to this zero
> page, page fault is triggered. Then page fault handler conclude that
> this is actually a write toward zero page from valid address, so it
> will allocate page(s).
>
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>
> blog: the-hydra.blogspot.com
> training: mulyaditraining.blogspot.com
>
>
>
> ------------------------------
>
> Message: 3
> Date: Sun, 2 Sep 2012 04:23:02 -0600
> From: Jim Cromie <jim.cromie at gmail.com>
> Subject: Re: Kernel booting problem.
> To: Sri Ram Vemulpali <sri.ram.gmu06 at gmail.com>
> Cc: Mulyadi Santosa <mulyadi.santosa at gmail.com>, Jonathan Neusch?fer
>         <j.neuschaefer at gmx.net>,        kernelnewbies at kernelnewbies.org
> Message-ID:
>         <CAJfuBxytc+u1W99QKA7HCR_Su1NRx=
> 1Qhn5MdLTKT_DYGpLuoQ at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> On Wed, Aug 29, 2012 at 10:06 PM, Sri Ram Vemulpali
> <sri.ram.gmu06 at gmail.com> wrote:
> > Thanks for the replies again.
> >
> > This time the problem is in tty specification.
> > Kernel supports console=tty0 (virtual terminal), where as my inittab has
> > entry ::sysinit:/sbin/getty -L ttyS0 vt100. I have to change the ttyS0
> to tty0.
> >
> > Once I changed this, I got login prompt.
> >
> > But I do not understand how we tell kernel to use ttyS0 over tty0.
> > Because in kernel config I selected was ttyS0 but it is using tty0.
>
> try console on boot-line
>
> root at voyage:~# more /proc/cmdline
> root=LABEL=ROOT_FS  console=ttyS0,115200n8  rootdelay=120 reboot=bios
> loglevel=8
>  dynamic_debug.verbose=1
>
> > Weird?
> >
> > Thanks,
> > Sri.
> >
>
>
>
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> End of Kernelnewbies Digest, Vol 22, Issue 1
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