[PATCH 05/15] ARM: head: use PC-relative insn sequence for __smp_alt

[Ard Biesheuvel]

On 11 August 2017 at 20:58, Nicolas Pitre <nicolas.pitre at linaro.org> wrote:
> On Fri, 11 Aug 2017, Ard Biesheuvel wrote:
>
>> On 11 August 2017 at 16:13, Tony Lindgren <tony at atomide.com> wrote:
>> > * Ard Biesheuvel <ard.biesheuvel at linaro.org> [170805 13:54]:
>> >> Replace the open coded PC relative offset calculations with a pair
>> >> of adr_l invocations.
>> >>
>> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> >> ---
>> >>  arch/arm/kernel/head.S | 12 ++----------
>> >>  1 file changed, 2 insertions(+), 10 deletions(-)
>> >>
>> >> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
>> >> index 6e9df3663a57..aed341e0f530 100644
>> >> --- a/arch/arm/kernel/head.S
>> >> +++ b/arch/arm/kernel/head.S
>> >> @@ -523,19 +523,11 @@ ARM_BE8(rev     r0, r0)                 @ byteswap if big endian
>> >>       retne   lr
>> >>
>> >>  __fixup_smp_on_up:
>> >> -     adr     r0, 1f
>> >> -     ldmia   r0, {r3 - r5}
>> >> -     sub     r3, r0, r3
>> >> -     add     r4, r4, r3
>> >> -     add     r5, r5, r3
>> >> +     adr_l   r4, __smpalt_begin
>> >> +     adr_l   r5, __smpalt_end
>> >>       b       __do_fixup_smp_on_up
>> >>  ENDPROC(__fixup_smp)
>> >>
>> >> -     .align
>> >> -1:   .word   .
>> >> -     .word   __smpalt_begin
>> >> -     .word   __smpalt_end
>> >> -
>> >>       .pushsection .data
>> >>       .globl  smp_on_up
>> >>  smp_on_up:
>> >
>> > Ard, it's this one that cause boot to fail on omap3.
>> > The rest of your set works for me with just this one
>> > left out.
>> >
>>
>> I'm completely puzzled.
>
> Found it.
>
> You replaced:
>
> -       adr     r0, 1f
> -       ldmia   r0, {r3 - r5}
> -       sub     r3, r0, r3
> -       add     r4, r4, r3
> -       add     r5, r5, r3
> +       adr_l   r4, __smpalt_begin
> +       adr_l   r5, __smpalt_end
>         b       __do_fixup_smp_on_up
>
> Notice that r3 is now uninitialized.
>
> Now have a look at the code for __do_fixup_smp_on_up.
>

I still don't see it :-)

__do_fixup_smp_on_up() mentions r3 in the comment block, but it does
not actually refer to it in the code, does it?