KERNELBASE and MMU

KERNELBASE and MMU

[Borlizzi Giacomo]

Hi,
I'm changing the operating system for my powerpc 860 board from
linux-2.2.13 to linux-2.4.0-test9.
With 2.2.13 version I have running the kernel and obtained the prompt of
sash .....
On 2.4 version it don't work instead.
My configuration foreseen  KERNELBASE set to 0x00000000 instead of
0xC0000000
this configuration seems be not  compatible with MMU initialization
code.
And infact during the execution of setup_arch() when the function
va_to_pte() is called
the  "mm = current->mm;" statment is executed (I report here some code)

pte_t *va_to_pte(unsigned long address)
{
 pgd_t *dir;
 pmd_t *pmd;
 pte_t *pte;
 struct mm_struct *mm;

 if (address < TASK_SIZE)           /* TASK_SIZE is 0x80000000 */
  mm = current->mm;                      <---this statment is executed
!!!
 else
  mm = &init_mm;

 dir = pgd_offset(mm, address & PAGE_MASK);
.......
.....

but at this moment "current" is not initialized????
on the 2.2.13 instead the function was have two parameters...

That is a big change... where I can found information on use of MMU on
860
and on means of those  data structures?

Thanks you in advanced and sorry for my bad English
/Giacomo Borlizzi


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Re: KERNELBASE and MMU

[Dan Malek]

Borlizzi Giacomo wrote:

> My configuration foreseen  KERNELBASE set to 0x00000000 instead of
> 0xC0000000

I don't really understand, but you should not be changing anything
in the source code or Makefiles or configuration files that affect
the MMU or virtual address mapping.


	-- Dan

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Re: KERNELBASE and MMU

[Borlizzi Giacomo]

Does you say that linux code is not PIC? (position indipendent code)
Why such constraint on physical memory area? It don't make some
limitation on portability of code?
/Giacomo Borlizzi



Dan Malek wrote:

> Borlizzi Giacomo wrote:
>
> > My configuration foreseen  KERNELBASE set to 0x00000000 instead of
> > 0xC0000000
>
> I don't really understand, but you should not be changing anything
> in the source code or Makefiles or configuration files that affect
> the MMU or virtual address mapping.
>
>         -- Dan


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Re: KERNELBASE and MMU

[Dan Malek]

Borlizzi Giacomo wrote:
>
> Does you say that linux code is not PIC? (position indipendent code)

No it is not.  You can move it around a little if you _really_
understand the details.  For any PowerPC processor there is no
reason to change the location regardless of the system implementation.

> Why such constraint on physical memory area? It don't make some
> limitation on portability of code?

No portability problem.  This code runs on more processors and
boards more easily than anything else in the world.


	-- Dan

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