[U-Boot] [PATCH v5 16/23] Adjust board_f.c for ppc

[Simon Glass]

Hi Scott,

On Tue, Feb 12, 2013 at 2:32 PM, Scott Wood <scottwood at freescale.com> wrote:
> On 02/08/2013 09:12:12 AM, Simon Glass wrote:
>>
>>  #ifndef CONFIG_SPL_BUILD
>>  static int reserve_stacks(void)
>>  {
>> +#ifdef CONFIG_PPC
>> +       ulong *s;
>> +#endif
>> +
>>         /* setup stack pointer for exceptions */
>>         gd->dest_addr_sp -= 16;
>>         gd->dest_addr_sp &= ~0xf;
>> @@ -398,6 +532,14 @@ static int reserve_stacks(void)
>>         /* leave 3 words for abort-stack, plus 1 for alignment */
>>         gd->dest_addr_sp -= 16;
>>
>> +#ifdef CONFIG_PPC
>> +       /* Clear initial stack frame */
>> +       s = (ulong *) gd->dest_addr_sp;
>> +       *s = 0; /* Terminate back chain */
>> +       *++s = 0; /* NULL return address */
>> +       gd->dest_addr_sp = (ulong) s;
>> +#endif
>> +
>
>
> PPC ABI requires 16-byte stack alignment, which would be broken by the
> CONFIG_USE_IRQ section (which even still has an "ARM ABI" comment).
>
> I think this entire function should be kept in arch code.  Stack layout is
> inherently architecture/ABI specific.  Some architectures even have a stack
> that grows upward (not sure if any such are supported by U-Boot).

Thanks for reviewing all this.

While I am working to avoid it, one option is to create a weak
function which archs can override. The reason I am keen to avoid it,
at least for a first implementation, is that it obscures the
similarities. In this case we could just just force 16-byte alignment,
and make the PPC code unconditional. It shouldn't hurt anything.

Regards,
Simon

>
> -Scott