Re: [Xenomai] [Xenomai-git] Jan Kiszka : cobalt/kernel: Remove unused mode parameter from COBALT_SYSCALL

[Philippe Gerum <rpm@xenomai.org>]

On 07/02/2015 07:03 PM, Gilles Chanteperdrix wrote:
> On Thu, Jul 02, 2015 at 06:56:00PM +0200, Philippe Gerum wrote:
>> On 07/02/2015 06:49 PM, Gilles Chanteperdrix wrote:
>>> On Thu, Jul 02, 2015 at 06:44:06PM +0200, Jan Kiszka wrote:
>>>> On 2015-07-02 18:30, Philippe Gerum wrote:
>>>>> On 07/02/2015 05:39 PM, Jan Kiszka wrote:
>>>>>> On 2015-07-02 17:24, Philippe Gerum wrote:
>>>>>>> On 07/02/2015 05:20 PM, git repository hosting wrote:
>>>>>>>> Module: xenomai-jki
>>>>>>>> Branch: for-forge
>>>>>>>> Commit: 99736c29a21a5e5536f8db9e580fd11cdb0eb0f2
>>>>>>>> URL:    http://git.xenomai.org/?p=xenomai-jki.git;a=commit;h=99736c29a21a5e5536f8db9e580fd11cdb0eb0f2
>>>>>>>>
>>>>>>>> Author: Jan Kiszka <jan.kiszka@siemens.com>
>>>>>>>> Date:   Thu Jul  2 17:12:39 2015 +0200
>>>>>>>>
>>>>>>>> cobalt/kernel: Remove unused mode parameter from COBALT_SYSCALL
>>>>>>>
>>>>>>> We want to keep this. At some point, maybe, we will be able to use this
>>>>>>> information to instrument the code with calling context guards, or as
>>>>>>> the source of the mode data in the syscall table. Today, it's at least
>>>>>>> useful inline documentation, without having to browse the table.
>>>>>>
>>>>>> This only makes sense when cobalt_sysmodes can be generated from it.
>>>>>> Currently it isn't, and I bet there are already plenty of
>>>>>> inconsistencies, minimizing the value captured via COBALT_SYSCALL
>>>>>> massively. So we should either get rid of cobalt_sysmodes or of that
>>>>>> parameter.
>>>>>>
>>>>>
>>>>> "currently" is the point. If you feel implementing either aspects, i.e.
>>>>> automatic tagging of the current context when traversing a cobalt call
>>>>> based on the mode in the syscall macro, or generating the table data
>>>>> based on the info, please do. If you feel fixing any consistency between
>>>>> the two mode specs proving your bet right, please do as well. But for
>>>>> now, I won't pick that commit.
>>>>
>>>> The approach of using COBALT_SYSCALL to define the mode only works if
>>>> that is also the only place to define it. Let's see first if/how that
>>>> can be achieved.
>>>
>>> That can be achieved by getting the macro to adding data in a
>>> special section, then use that section as the syscall table with
>>> linker generate symbols. A lot of stuff works like this, like the
>>> init table, or glibc constructors, so, this can definitely be
>>> achieved. This probably requires the I-pipe patch to modify the
>>> kernel linker script, of which there are several instances (one
>>> instance by arch maybe).
>>>
>>
>> Yes. Having to fixup the linker script was the reason not to implement
>> this immediately, as there could be some backward compat issues to
>> address with legacy pipelines running a most recent 3x cobalt core.
> 
> The linker script uses wildcards, maybe we can use a section name in
> that namespace to avoid changing the script.
> 

I was referring to the Xenomai side, properly handling kernels patched
with pipelines supporting the feature or not.

-- 
Philippe.