Re: [Xen-devel] [PATCH v2 for 4.5] arm32: fix build after 063188f4b3

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 10/13/2014 06:01 PM, Stefano Stabellini wrote:
> On Mon, 13 Oct 2014, Julien Grall wrote:
>> Hi Stefano,
>>
>> On 10/13/2014 05:06 PM, Stefano Stabellini wrote:
>>>> +int do_smc(register_t function_id, ...);
>>>
>>> I am not sure whether this is safe: the smc calling convention on arm64
>>> doesn't promise to save the x0-x17 registers. The smc calling convention
>>> on arm32 only promises to save r4-r15. That means that after issuing an
>>> smc call with just two arguments, you could still find r3 to be changed
>>> afterwards.
>>> I think you'll have to manually save/restore all the registers outside
>>> the safety guarantees of the smc protocol.
>>
>> The calling convention specifies:
>>      - r0-r3 as argument/scratch register on ARM32
>>      - x0-x17 as argument/temporary register on ARM64
>>
>> So we don't need to save/restore them before/after calling the SMC function.
> 
> I think you are right.

I will resend a patch with Jan comments.

-- 
Julien Grall

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