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Date: Fri, 6 Apr 2012 00:53:04 +0400
From: Cyrill Gorcunov <gorcunov@openvz.org>
To: Matt Helsley <matthltc@us.ibm.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>,
        Oleg Nesterov <oleg@redhat.com>,
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        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 6/7] mm: kill vma flag VM_EXECUTABLE
Message-ID: <20120405205304.GL8718@moon>
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On Thu, Apr 05, 2012 at 01:29:04PM -0700, Matt Helsley wrote:
...
> > > Doesn't that break the semantics of the kernel ABI?
> > 
> > Which one? exe_file can be changed iif there is no MAP_EXECUTABLE left.
> > Still, once assigned (via this prctl) the mm_struct::exe_file can't be changed
> > again, until program exit.
> 
> The prctl() interface itself is fine as it stands now.
> 
> As far as I can tell Konstantin is proposing that we remove the unusual
> counter that tracks the number of mappings of the exe_file and require
> userspace use the prctl() to drop the last reference. That's what I think
> will break the ABI because after that change you *must* change userspace
> code to use the prctl(). It's an ABI change because the same sequence of
> system calls with the same input bits produces different behavior.

Hi Matt, I see what you mean (I misread your email at first, sorry).
Sure it's impossible to patch already existing programs (and btw, this
prctl code actually won't help a program to drop symlink completely
and live without it then, because old one will gone but new one
will be assigned) so personally I can't answer here on Konstantin's
behalf, but I guess the main question is -- which programs use this
'drop-all-MAP_EXECUTABLE' feature?

	Cyrill