about real-base, real-size

[Ryan Wang]

Thanks a lot.

2011/10/19 Tony Breeds <tony at bakeyournoodle.com>

> On Tue, Oct 18, 2011 at 09:22:21PM +0800, Ryan Wang wrote:
> > Hi,
> >
> > I do not really understand real-base/real-size and have some questions:
> >       1) Is "real-base + real-size" the memory seen by client OS, AIX or
> > Linux?
> >           Or it's just for the kernel image, e.g vmlinux for Linux?
> >       2) What about yaboot? Where is is loaded to in the memory?
> >           If yaboot uses "real-base + real-size", where is the kernel
> image
> > loaded?
>
> real-base is the address that OpenFirmware (OF) is loaded at, and real-size
> is the ammount of menory that (OF) is using.  The memory seen by the
> boot loader varies.  If you're in real mode (for example on an IBM
> pSeries system) You only see the first LMB (typically 128 or 256MB)  If
> you're in virtual mode, then the boot loader sees all the memory in the
> system.
>
> The client OS (Linux or AIX) can interrogate the device-tree to
> determine the full system memory and then control the MMU to acces it.
>
> Another envirnoment var similar to real-base and real-size is load-base
> which is where images loded by OF will be placed until the ELF headers
> are processed.
>
> So on a pSeries system booting yaboot the memory layout will look
> something like
>
> load-base=16KB
> real-base=12MB
> real-size=16MB
> 128MB of Real Mode Addressable memory (RMA)
>
>    0 ->  16KB  Interrupt vectors
>  16KB ->  14KB  yaboot ELF image
>  1MB ->   3MB  yaboot text and data
>  -------------  Small ammounts of memory claim()ed by yaboot, eg the
>                Malloc space
>  12MB ->  28MB  OF
>  28MB ->  40MB  vmlinux ELF image
>  64MB ->  96MB  vmlinux text and data
>  96MB -> 110MB  initrd
>
> Once the kernel is booted this all changes. but I hope that helps a
> little.  Netbooting makes this even tighter.
>
> Yours Tony
>
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