Re: [Prex-devel] sp pointer in umem_* functions

[pradeep s. <pra...@gm...>]

Sorry for the  previous incomplete mail.
I was going through umem_strnlen function defined in sys/arch/arm/arm/locore.S :

       mov     r12, sp
       stmdb   sp!, {r4, r11, r12, lr, pc}
       mov     r4, r0
       sub     r11, r12, #4
       cmp     r0, #(UMEM_MAX)
       bhi     umem_fault
       b       2f
1:      add     r0, r0, #1
2:      subs    r1, r1, #1
       bcc     3f
known_fault3:                           /* May be fault here */
       ldrb    r3, [r0]
       cmp     r3, #0
       bne     1b
3:      rsb     r0, r4, r0
       str     r0, [r2]
       mov     r0, #0                  /* Set no error */
       ldmia   sp, {r4, r11, sp, pc}

At entry, r12 contains old sp pointer and 5 registers are pushed on
the stack. But at exit only 4 registers are popped out.
Why is pc pushed on the stack at entry ?
Regards,
Pradeep

On Wed, Jul 22, 2009 at 1:45 PM, pradeep
sawlani<pra...@gm...> wrote:
> Hello ,
> I was going through umem_strnlen function defined in sys/arch/arm/arm/locore.S :
>
>        mov     r12, sp
>        stmdb   sp!, {r4, r11, r12, lr, pc}
>        mov     r4, r0
>        sub     r11, r12, #4
>        cmp     r0, #(UMEM_MAX)
>        bhi     umem_fault
>        b       2f
> 1:      add     r0, r0, #1
> 2:      subs    r1, r1, #1
>        bcc     3f
> known_fault3:                           /* May be fault here */
>        ldrb    r3, [r0]
>        cmp     r3, #0
>        bne     1b
> 3:      rsb     r0, r4, r0
>        str     r0, [r2]
>        mov     r0, #0                  /* Set no error */
>        ldmia   sp, {r4, r11, sp, pc}
>