Re: [LTP] clone tests fails

Michal Simek
2010-01-06T10:20:57Z

Serge E. Hallyn wrote:
> Quoting Jiri Palecek (jpalecek@web.de):
>> Serge E. Hallyn napsal(a):
>>> Quoting Michal Simek (michal.simek@petalogix.com):
>>>> Serge E. Hallyn wrote:
>>>>> Quoting Michal Simek (michal.simek@petalogix.com):
>>>>>> Hi Mike,
>>>>>>
>>>>>> I have one question about one your big patch
>>>>>>
>>>>>> http://git.kernel.org/?p=linux/kernel/git/galak/ltp.git;a=commitdiff;h=391dc18fe3271fbf2ca1864a5299f091c31e0018
>>>>>>
>>>>>> My question is why you add -1 in lib/cloner.c:65
>>>>>>
>>>>>> + ret = clone(fn, (stack ? stack + stack_size - 1 : NULL),
>>>>>> + clone_flags, arg);
>>>>>>
>>>>>> In previous code in clone testcases was nothing like this.
>>>>>> What reason have you had to add it?
>>>>> Because the same thing was done in lots of places all over the
>>>>> testsuite (and done wrong). This consolidates them all.
>>>>
>>>> I don't have anything against consolidation. I just want to know why
>>>> there is that -1 which weren't in any clone testcases. Nothing more
>>>> nothing less.
>>> ooooh. Because if we've done stack = malloc(stack_size), then
>>> stack+stack_size is 1 above the the top of stack.
>> If the value of the parameter is the stack pointer of the created
>> thread, it shouldn't matter - the address should never be used (read
>> or written).
>>
>> Michal, I suspect the failures you see are somehow related to
>> alignment (that your architecture doesn't like odd addresses). Is
>> that right? Under x86, the address gets aligned (so some of the
>> space is unused).
>>
>> Perhaps both of these behaviors should be tested by LTP?
>
> Gah, yes, Nathan had mentioned arches where this matters (including
> some power?). Nathan, did you have a generic fix for this in
> userspace? Should always be safe to do
> (stack + stack_size - 1) & ~0xf
> ?

(long)(stack + stack_size - 1) & ~0x3

0x3 is enough - just clear last 2 bits.
I am not sure about long type - maybe need long long or long double.

Mike's solution not work for me.

Thanks,
Michal

>
> -serge

--
Michal Simek, Ing. (M.Eng)
PetaLogix - Linux Solutions for a Reconfigurable World
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