Interesting case while taking Ramdump of Linux kernel based device

[sandeep kumar]

Hi vladimir
>I think this kind of behaviour could be configurable. In case you have
>described bootloader can protect its code. Actually, kernel does not
>know itself how much RAM is presented. Bootloader must provide kernel
>with memory configuration through ATAGs (see mem boot option).
>Therefore, bootloader can reserve some RAM for itself and does not say
>kernel about it. As you have already get kernel use all memory which
>is provided with bootloader and it is not always an entry RAM.

In our bootloader, it seems they arent sending any ATAG_MEM as such,
but the are calling start_kernel() function, in which start_kernel is a
'type casted function pointer'
of the "kernel starting address".

if ATAG_MEM is not sent..how wil the kernel treat the available memory.

By the way ATAG_MEM has only start memory address.
How to specify that "this much memory need to be reserved" for bootloader?

On Mon, Jul 25, 2011 at 10:49 AM, Vladimir Murzin <murzin.v at gmail.com>wrote:

> Hi sandeep!
>
> On 7/25/11, sandeep kumar <coolsandyforyou at gmail.com> wrote:
> > Hi all,
> > In Android target mobiles there is a facility called "Ramdump", where the
> > entire Ram image is copied to a file
> > as the kernel goes to panic.
> >
> > Ramdump is implemented like this
> > 1) As the panic() function is called target will be reset.
> > 2) Bootloader boots up in specific mode, where it enables the USB driver
> in
> > uploading mode.
> > 3) Through USB entire RAM content is copied to a file in the host
> computer.
> > 4) This file is parsed through different tools and we can get the logs
> info
> > wat exactly happened just before kernel panic happend.
> >
> >
> > Now here is the interesting part,
> > While the mobile's RAM image is being uploaded to host computer, our
> > bootloader is still running in the mobile's RAM.
> > How can it copy its own running region.
> >
> > This triggered me the following questions,
> >
> > 1) When bootloader runs, will it run in a specific reserved region of RAM
> or
> > it takes entire RAM?
>
> AFAIK, it runs in specific region. For instance, for Das U-boot
> bootloader you can get this with
> $file ./uImage
> uImage: u-boot legacy uImage, Linux-2.6.35-g6d019da-dirty, Linux/ARM,
> OS Kernel Image (Not compressed), 2733288 bytes, Thu Sep  2 01:11:09
> 2010, Load Address: 0x80008000, Entry Point: 0x80008000, Header CRC:
> 0xEA95BF09, Data CRC: 0xF652AF6B
>
> > 2) When it hands over the control to kernel, will it relinquish the
> entire
> > RAM or certain part of RAM is reserved for it?
> > 3) Does kernel use the entire RAM while running?
>
> I think this kind of behaviour could be configurable. In case you have
> described bootloader can protect its code. Actually, kernel does not
> know itself how much RAM is presented. Bootloader must provide kernel
> with memory configuration through ATAGs (see mem boot option).
> Therefore, bootloader can reserve some RAM for itself and does not say
> kernel about it. As you have already get kernel use all memory which
> is provided with bootloader and it is not always an entry RAM.
>
> > 4) When the kernel is running, is ther any chance that, control again be
> > taken back to bootloader?(coz i saw in bootloader code kernel is being
> > called,
> >
> > after that code also some code is there,some printks and error handling
> > stuff)
> >
> > Pls help me out here..
> >
> >
> >
> > --
> > With regards,
> > Sandeep Kumar Anantapalli,
> >
>



-- 
With regards,
Sandeep Kumar Anantapalli,
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