v7-M: Fixing XIP when the kernel is in ROM

[Ezequiel Garcia]

On 27 October 2015 at 18:33, Maxime Coquelin <mcoquelin.stm32 at gmail.com> wrote:
> 2015-10-27 21:33 GMT+01:00 Stefan Agner <stefan at agner.ch>:
>> On 2015-10-27 13:25, Maxime Coquelin wrote:
>>> 2015-10-27 17:03 GMT+01:00 Maxime Coquelin <maxime.coquelin at st.com>:
>>>> Hi Ezequiel,
>>>>
>>>> On 10/27/2015 04:35 PM, Ezequiel Garcia wrote:
>>>>>>
>>>>>> >>>The temporary stack is allocated in the .text.init section
>>>>>> >>>and so this doesn't work when the kernel is executing from ROM.
>>>>>
>>>>> >>
>>>>> >>If sp isn't used, how does it break you setup?
>>>>
>>>> STM32 machine works fine with XIP from internal flash memory, so as Uwe, I'm
>>>> surprised it solves your problem.
>>>>
>>>> I will have a try with your patch later today.
>>>
>>> Just tested, and confirm it works with (and without) your patch in XIP on STM32.
>>
>> It probably depends what exactly happens when the CPU core tries to use
>> the stack. I mean, the CPU core will issue a write to the flash, and how
>> that behaves is probably implementation specific. However, I would
>> expect that it should lead to some kind of fault... Do we have fault
>> handlers at that time?
>
> Yes we have fault handlers at that time.
> I agree the behaviour is probably implementation specific.
>
>>
>> Anyway, I guess Ezequiel's fix is the right thing to do...
> Or, maybe we should put the stack in RAM as Uwe suggest?
>

It seems the current fix would be used as-is (no need to
set a temporary stack before the SVC call).

And on top of that, we need a to set a proper stack as soon
as the kernel takes control.

Am I right?
-- 
Ezequiel García, VanguardiaSur
www.vanguardiasur.com.ar