Re: [LTP] clone tests fails

["Serge E. Hallyn" <serue@us.ibm.com>]

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
?

-serge

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