sp uninitialized in imx6_cpu_lowlevel_init

sp uninitialized in imx6_cpu_lowlevel_init

[Uwe Kleine-König]

Hello,

when building imx_v7_defconfig and then looking at
images/start_imx6_gk802.pbl (several more are affected, too), I get:

$ objdump -d images/start_imx6_gk802.pbl
00000000 <start_imx6_gk802>:
   0:   e28f9001        add     r9, pc, #1
   4:   e12fff19        bx      r9
   8:   f000 f822       bl      50 <start_imx6_gk802+0x50>
...
  50:   f000 f850       bl      f4 <__start_imx6_gk802>
...
  f4:   f000 f80c       bl      110 <imx6_cpu_lowlevel_init>
...
 110:   b508            push    {r3, lr}

That is the sp register is used here without being initialized. I guess
this didn't break up to now because when barebox is jumped into, sp
was already used by the boot rom and still points into SRAM.

Still I think this is worth to be fixed. I think this means that
imx6_cpu_lowlevel_init must be marked __naked and lr must be saved into
a register that is preserved by the functions called by
imx6_cpu_lowlevel_init.

Sounds reasonable?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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Re: sp uninitialized in imx6_cpu_lowlevel_init

[Sascha Hauer]

On Fri, Jan 16, 2015 at 09:27:28PM +0100, Uwe Kleine-König wrote:
> Hello,
> 
> when building imx_v7_defconfig and then looking at
> images/start_imx6_gk802.pbl (several more are affected, too), I get:
> 
> $ objdump -d images/start_imx6_gk802.pbl
> 00000000 <start_imx6_gk802>:
>    0:   e28f9001        add     r9, pc, #1
>    4:   e12fff19        bx      r9
>    8:   f000 f822       bl      50 <start_imx6_gk802+0x50>
> ...
>   50:   f000 f850       bl      f4 <__start_imx6_gk802>
> ...
>   f4:   f000 f80c       bl      110 <imx6_cpu_lowlevel_init>
> ...
>  110:   b508            push    {r3, lr}
> 
> That is the sp register is used here without being initialized. I guess
> this didn't break up to now because when barebox is jumped into, sp
> was already used by the boot rom and still points into SRAM.
> 
> Still I think this is worth to be fixed. I think this means that
> imx6_cpu_lowlevel_init must be marked __naked and lr must be saved into
> a register that is preserved by the functions called by
> imx6_cpu_lowlevel_init.
> 
> Sounds reasonable?

I think we should rather setup a stack before calling
imx6_cpu_lowlevel_init. We have SRAM for that so we can use it.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
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