Subject: Re: ppc manual paging question

From: "Wang, Baojun" <[email-masked]>
Date: Fri, 26 Oct 2007 17:50:51 +0800

On Monday 22 October 2007 16:04:14, Benjamin Herrenschmidt wrote：
> > Yup, I've found how does the kernel handle tlbs, I think the most
> > important thing is I forgot read/write the SPRN_SPRG3 register as _switch
> > does.
>
> SPRG3 is for use by the operating system for whatever you want... if you
> are copying linux code, then you probably indeed want to get that right
> but you don't have to use SPRG3.
>
> > I've add the _PAGE_PRESENT flag to the related PTE
>
> Hrm.. that has nothing ot do with the PTE. Bolting is more a property of
> your replacement algorithm in the TLB miss handler.
>
> Ben.

Hi,

  First thanks a lot for your help I've finish the tlb code, now I can 
manually translate the virtual address correctly, I verified this by printing 
out the data within the virtual address and it's fine. now the only thing 
left is jump to that address (the address is point to _start function), But I 
got an error about unable to access the stack (0xd100fc60 ...), but it is 
valid before the instruction:

/**
 * XXX: should not defined here
 */
#define EVENTS_USER_ADDR_OFFSET 36

_GLOBAL(jump_xm_dom)
        stwu    r1,-INT_FRAME_SIZE(r1)
        mflr    r0
        stw     r0,INT_FRAME_SIZE+4(r1)

        stw     r31,INT_FRAME_SIZE+128(r1)

        lwz     r5,EVENTS_USER_ADDR_OFFSET(r4)
        mr      r31,r5  /* new_domain->events_user_addr */

        cmpwi   r3,0
        beq     1f

        mtctr   r3      /* jump to entry_point */
        bctrl

        li      r3,0
1:
        lwz     r31,INT_FRAME_SIZE+128(r1)

        lwz     r0,INT_FRAME_SIZE+4(r1)
        addi    r1,r1,INT_FRAME_SIZE
        mtlr    r0
        blr

the SP is valid before `bctrl', while exec bctrl, I got the error said unable 
to access address SP ($r1) from bdigdb, without bdigbd (running directly), an 
error is print out while the system is dead: 

insn: 94 21 ff 40 7c 08 02 a6 90 01 00 c4 7f e3 fb 78 3d 20 10 01 90 69 07 a0 
48 00 02 55 80 01 00 c4
$T0440:10000094;01:d1072e60;#ee

address d1072e60 is the address of SP ($r1) before bctrl.

NOTE entry_point($r3) is address like 0x100000a0 which is loaded from the 
userspace by a loader program (it loads all section marked as PT_LOAD, such 
as .text, the above insn is the entry of .text section, which is _start), but 
the above code is from the kernel space. and here is the _start function:

#define INT_FRAME_SIZE  192

.globl _start
_start:
        stwu    1, -INT_FRAME_SIZE(1)
        mflr    0
        stw     0, INT_FRAME_SIZE+4(1)

        mr      3,31    /* new_domain->events_user_addr */

        lis     9, event_handling@ha
        stw     3, event_handling@l(9)
        bl      kmain

        lwz     0, INT_FRAME_SIZE+4(1);
        mtlr    0
        addi    1, 1, INT_FRAME_SIZE
        blr

.size   _start, .-_start

I'm sorry I'm not very familiar with the ppc assembly, is there something 
fundamentally wrong? Thank you very much!

  Regards,
Wang

-- 
Wang, Baojun                                        Lanzhou University
Distributed & Embedded System Lab              http://dslab.lzu.edu.cn
School of Information Science and Engeneering        [email-masked]
Tianshui South Road 222. Lanzhou 730000                     .P.R.China
Tel:+86-931-8912025                                Fax:+86-931-8912022