Re: x86: get rid of the insane TIF_ABI_PENDING bit

[Andi Kleen <andi@firstfloor.org>]

On Tue, Feb 16, 2010 at 11:19:03AM +0100, Oleg Nesterov wrote:
> On 02/15, H. Peter Anvin wrote:
> >
> > On 02/15/2010 11:41 AM, Roland McGrath wrote:
> > > It affects whatever uses is_compat_task(), but I can't see anything
> > > where that matters except inside some particular syscall or for
> > > syscall restart after signals.
> >
> > FWIW, the origin of this is checkin
> > 4d9bc79cd28b779610d9590b3a96a28a0f64a25a (2.6.18-rc1), which somewhat
> > unhelpfully states "Make sure is_compat_task works early".  It doesn't
> > specify what the failure is if is_compat_task doesn't work early.
> 
> Perhaps Andi could explain us why this is needed,
> 
> > On
> > the other hand, it sure as heck seems better to set it and not need it
> > than the other way around.
> 
> Agreed, but otoh it is always good to understand the code. If we
> really have a reason for TS_COMPAT, a small comment can help other
> readers.

My memory is somewhat fuzzy on this one, but I think it was related
to VMA placement (probably for stack randomization or something like that)
This happens before the first call. I might be wrong on that.

There might also have been other is_compat_task checks in the exec init
path, so partly it was defensive programming.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.