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Re: Preventing preemption of 'protected' symbols in GNU ld 2.26 [aka should we revert the fix for 65248]


On Tue, Apr 19, 2016 at 7:06 AM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Tue, 19 Apr 2016, Richard Biener wrote:
>
>> So with all this it sounds that current protected visibility is just
>> broken and we should forgo with it, making it equal to default
>> visibility?
>
> Like how?  You mean in GCC regarding protected as default visibility?  No,
> that's just throwing out the baby with the water.  We should make
> protected do what it was intended to do and accept that not all invariants
> that are true for default visible symbols are also true for protected
> symbols, possibly by ...
>
>> At least I couldn't decipher a solution that solves all of the issues
>> with protected visibility apart from trying to error at link-time (or
>> runtime?) for the cases that are tricky (impossible?) to solve.
>

Protected visibility is a useful feature.  But as it stands today,
it is pretty much useless on x86 as seen in ld and ld.so.  We
have known this defect for a long time, almost from day 1.  To
make it truly useful, we need to clearly spell out how and when
it can be used.  We should enforce its limitation in compiler,
ld and ld.so so that there is no surprise, either for correctness or
performance,  at run-time.


-- 
H.J.


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