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Is it possible to call a C function in transfer_to_handler(arch/ppc/kernel/entry.S)?

DISCUSSION Wang, Baojun 3 participants 3 messages May 28, 2007

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Wang, Baojun

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#0 lore raw

hi, list

I'm sorry to ask this topic in this mailling list. I've spend more than 2
days try to add a C function call in transfer_to_handler(in arch/ppc/kernel/entry.S) like this:

/* cut from arch/ppc/kernel/entry.S */
transfer_to_handler:

        stw     r2,GPR2(r11)
        stw     r12,_NIP(r11)
        stw     r9,_MSR(r11)
        andi.   r2,r9,MSR_PR
        mfctr   r12
        mfspr   r2,SPRN_XER
        stw     r12,_CTR(r11)
        stw     r2,_XER(r11)
        mfspr   r12,SPRN_SPRG3
        addi    r2,r12,-THREAD
        tovirt(r2,r2)                   /* set r2 to current */
        beq     2f                      /* if from user, fix up THREAD.regs */
#if 1	/* this is add by me */
        stwu    r1, -16(r1)
        mflr    r0
        stw     r0, 20(r1)
        bl      emulate_iret
        lwz     r0, 20(r1)
        mtlr    r0
        addi    r1, r1, 16
#endif
        addi    r11,r1,STACK_FRAME_OVERHEAD
        stw     r11,PT_REGS(r12)

The function prolog is taken from a userspace program. this code freeze the system after prints out `emulate_iret' (The only thing function emulate_iret do is print that message).

I read the source code from head_44x.S to entry.S, sounds like all registers (r0-r32, and even more such as _LINK, _CTR, etc..) are being saved, does that mean I shouldn't call any C function in transfer_to_handler()? Is there something tricky (or is it possible) to add a C function call?

Thanks in advance!

regards

Signature · 5 lines
Wang, Baojun                                        Lanzhou University
Distributed & Embedded System Lab              http://dslab.lzu.edu.cn
School of Information Science and Engeneering        [email protected]
Tianshui South Road 222. Lanzhou 730000                     .P.R.China
Tel:+86-931-8912025                                Fax:+86-931-8912022
#1 lore raw
Quoted 3 lines · Baojun

I'm sorry to ask this topic in this mailling list. I've spend more than 2
days try to add a C function call in transfer_to_handler(in arch/ppc/kernel/entry.S) like this:

It's not going to work, because the MMU is off at this point. It will explode as soon as the C code tries to touch any external variable.

Paul.

#2 lore raw
In reply to Wang, Baojun

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Quoted 5 lines

I'm sorry to ask this topic in this mailling list. I've spend more than 2
days try to add a C function call in transfer_to_handler(in arch/ppc/kernel/entry.S) like this:

Why are you sorry ? This is what this list is for - and if nobody can answer it then its good you sent it - thanks !

<snip...>

Quoted 1 line

#if 1 /* this is add by me */

could you change this to use onle R3-R13 as these are caller safe - My suspicion i sthat you are using R0/1/2 and that is not healthy here.

Quoted 11 lines
       stwu    r1, -16(r1)
       mflr    r0
       stw     r0, 20(r1)
       bl      emulate_iret
       lwz     r0, 20(r1)
       mtlr    r0
       addi    r1, r1, 16
#endif
       addi    r11,r1,STACK_FRAME_OVERHEAD
       stw     r11,PT_REGS(r12)

out of PPC too long - but will see if I can find something.

hofrat
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