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Re: [PATCH] Remove unnecessary IFUNC dispatch for __memset_chk.


On Tue, Aug 11, 2015 at 12:55:31PM -0700, H.J. Lu wrote:
> On Tue, Aug 11, 2015 at 12:41 PM, Alexander Monakov <amonakov@ispras.ru> wrote:
> > On Tue, 11 Aug 2015, H.J. Lu wrote:
> >> > Didn't know its explicitly forbidden to use nonstatic resolvers. Do we document that requirement somewhere?
> >> > If not then we should add it to documentation.
> >>
> >> It makes no senses for IFUNC selector to return the address of
> >> a global function, which may be preempted at run-time.
> >
> > That would be imposing a policy while providing a mechanism.
> >
> > I think there are plausible scenarios where returning a global function from
> > an ifunc resolver would be natural.
> >
> > To give a specific example, imagine an ifunc symbol
> > 'printf_fortified_opportunistically', which resolves to 'printf_chk' if it is
> > available in the global namespace, or normal 'printf' otherwise.
> >
> > Such a symbol could be in any DSO, not necessarily libc, and thus it has to be
> > able to pick up global symbol definitions.
> >
> 
> By the nature of preemption, you have NO control over which definition
> will be used at run-time.  It can be literally anything, including segfault.
>
Could you document that somewhere? Sorry for earlier confusion where I
thought you meant resolver must be static. Its about that users could
have similar ideas like making symbol global for silly reasons like
 be able to profile variant with LD_PRELOAD.


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