Re: [Xenomai] Mayday mechanism broken on x86-64 - simpler approach feasible?

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2015-02-12 18:19, Jan Kiszka wrote:
> On 2015-02-12 18:18, Philippe Gerum wrote:
>> On 02/12/2015 06:16 PM, Jan Kiszka wrote:
>>> On 2015-02-12 18:07, Philippe Gerum wrote:
>>>> On 02/12/2015 06:02 PM, Jan Kiszka wrote:
>>>>> On 2015-02-12 17:36, Jan Kiszka wrote:
>>>>>>> As I mentioned earlier, I'd rather fix the MAYDAY implementation for
>>>>>>> x86_64 instead of forking the implementation between MMU-enabled and
>>>>>>> MMU-less architectures, also affecting powerpc, arm and x86_32 in the
>>>>>>> same move. Fortunately, the current implementation allows very specific
>>>>>>> tweaks to be applied on a per-architecture basis. This one fixes the
>>>>>>> issue for Cobalt on x86_64, and could be easily backported to 2.6.x:
>>>>>>>
>>>>>>> http://git.xenomai.org/xenomai-3.git/commit/?h=next&id=6db20901963d634b9786467c711c2ba526db48a2
>>>>>>
>>>>>> Looks almost good - except for the detail that some bits of the
>>>>>> instruction pointer are lost on return from the syscall (int vs. long
>>>>>> return type). Patches in the making.
>>>>>
>>>>> Will take longer - I need to convert all cobalt syscalls.
>>>>>
>>>>> We have a sleeping bug there, though likely not seen in practice, with
>>>>> syscalls returning values > INT_MAX (size_t...). The problem is that
>>>>> handle_head/root_syscall only forwarded 32-bits so far.
>>>>>
>>>>
>>>> You mean this, and all the implications of it?
>>>>
>>>> diff --git a/kernel/cobalt/posix/syscall.c b/kernel/cobalt/posix/syscall.c
>>>> index 6a9a02c..99b86a4 100644
>>>> --- a/kernel/cobalt/posix/syscall.c
>>>> +++ b/kernel/cobalt/posix/syscall.c
>>>> @@ -73,9 +73,9 @@
>>>>  /* Shorthand for oneway trap - does not return to call site. */
>>>>  #define __xn_exec_oneway    __xn_exec_norestart
>>>>
>>>> -typedef int (*cobalt_syshand)(unsigned long arg1, unsigned long arg2,
>>>> -			      unsigned long arg3, unsigned long arg4,
>>>> -			      unsigned long arg5);
>>>> +typedef long (*cobalt_syshand)(unsigned long arg1, unsigned long arg2,
>>>> +			       unsigned long arg3, unsigned long arg4,
>>>> +			       unsigned long arg5);
>>>>
>>>>  static void prepare_for_signal(struct task_struct *p,
>>>>  			       struct xnthread *thread,
>>>>
>>>
>>> Exactly.
>>>
>>> Just done with the mechanics, crossing fingers it won't break things subtly.
>>>
>>
>> Ok. While we are at it, we should get rid of the syscall return type in
>> the COBALT_SYSCALL[_DECL] macro helpers, this is pointless.
> 
> Jep, that's what I did - hard-wired it to long.
> 
> First tests look good, just need to split things up into 3 or 4 patches now.

Done, see my for-forge branch.

Jan

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