Re: [MiNT] [PATCH] Make EHCI driver interrupt handler follow PCI-BIOS specification.

[Alan Hourihane <alanh@fairlite.co.uk>]

On 08/10/14 16:31, David Gálvez wrote:
> 2014-10-08 14:08 GMT+02:00 Vincent Rivière <vincent.riviere@freesbee.fr>:
>> On 08/10/2014 11:44, David Gálvez wrote:
>>> +       asm volatile("move.l d1,-(SP)\n\t" : : : );
>>
>> I'm really not sure that this block does what you think (and I'm pretty sure
>> it does not).
>> By doing so, you modify SP, but GCC does not know that. Afterwards, it may
>> access local variables or parameters through SP. If you change SP, those
>> references will be wrong.
>>
>> The only safe way to preserve registers in a callback is to implement it as
>> a full assembler stub (in a .S file). So it can save/restore the registers,
>> get the parameters and call a standard C function containing the main
>> callback code.
>>
>
> Thanks Vincent for taking a look to the patch and also for the advice,
> I'll review it.
> The code has been tested and it's working but I understand that could
> be just luck.
>
>

I think you're just being lucky, because you restore the registers later.

But essentially, I think this step is a no-op, because GCC will save/restore
it's accessed registers anyway.

Also, you save/restore D1/A1 but the comment says D0/A0.

Alan.