On 9.3.18 19:40, The Natural Philosopher wrote:
> On 09/03/18 13:56, Tauno Voipio wrote:
>> On 9.3.18 11:30, The Natural Philosopher wrote:
>>> On 09/03/18 09:17, Richard Kettlewell wrote:
>>>> The Natural Philosopher  writes:
>>>>> On 08/03/18 17:33, mm0fmf wrote:
>>>>>> On 08/03/2018 15:27, Martin Gregorie wrote:
>>>>>>> On Thu, 08 Mar 2018 13:34:57 +0000, The Natural Philosopher wrote:
>>>>>>>> I would at least put in a bit more
>>>>>>>>
>>>>>>>> int myfunction(int bufflth, char* buff)
>>>>>>>>       {
>>>>>>>>          return (int)buff[bufflth-1];
>>>>>>>>       }
>>>>>>>>
>>>>>>>> So you know where on the stack buff and bufflth are...
>>>>>>>
>>>>>>> Why would you want to know that? All the assembler operations
>>>>>>> using the
>>>>>>> arguments will be inside myfunction() and, unless the code is
>>>>>>> calculating
>>>>>>> a result to be returned and used elsewhere, the returned value is
>>>>>>> probably to report success or failure.
>>>>>>>
>>>>>>
>>>>>> If it returns success or failure, why return 1 of 4 billion possible
>>>>>> values?
>>>>>
>>>>> Another personm who has never coded assmebler for C..
>>>>>
>>>>> It not what you are rurining, its how to access (bufflth, char* buff)
>>>>> which are LOCAL stack based variables.
>>>>
>>>> The first few args are passed in registers on many modern systems. See
>>>> e.g.
>>>>
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042f/IHI0042F_aapcs.pdf
>>>>
>>>> for instance.
>>>>
>>>
>>> Even so, the method still reveals WHICH registers
>>>
>>> But it is not a feature of the ARM per se, merely a convention.
>>>
>>> I assume gcc follows it, but there is no gurantee
>>
>> GCC follows the ARM EABI specification:
>>
>>   - stack on 8 byte boundaries,
>>   - arguments in r0 - r3
>>   - return value in r0
>>
>> I still suspect that the OP does not have a clue of the assembly
>> code he's attempting to link in.
>>
> That is very useful info, which I will remember in case I ever program
> an ARM chip in assembler...

It is doable, but needs some care. Using the GCC embedded assembly
with access to C variables makes the thing a bit easier.

Been there - done that (some RT kernels).

> Your final sentence?

The OP has been loudly silent on my posts, so there is only a guess ...

--

-TV

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