On 02/12/2013 04:41:15 PM, Simon Glass wrote:
Hi Scott,
On Tue, Feb 12, 2013 at 2:32 PM, Scott Wood <scottw...@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.
That's fine for most of the file, but I think there's not much that's
truly generic when it comes to setting up the stack. It's not as if
this is a huge function (at least before it grows a bunch of ifdefs).
In this case we could just just force 16-byte alignment,
and make the PPC code unconditional. It shouldn't hurt anything.
The CONFIG_USE_IRQ section also has references to FIQs... if it's meant
to be an ARM-specific CONFIG, perhaps it should be renamed (and
definitely it should be documented).
-Scott
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