about real-base, real-size
tony at bakeyournoodle.com
Wed Oct 19 09:38:55 EST 2011
On Tue, Oct 18, 2011 at 09:22:21PM +0800, Ryan Wang wrote:
> 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
> 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
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
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
So on a pSeries system booting yaboot the memory layout will look
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
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.
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