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

[Jeff Law]

On 04/18/2016 11:55 AM, Cary Coutant wrote:
>>> That is why protected visibility is such a mess.
>>
>> Not mess, but it comes with certain limitations.  And that's okay.  It's
>> intended as an optimization, and it should do that optimization if
>> requested, and error out if it can't be done for whatever reason.
>
> I completely agree.
ISTM this ought to be the guiding principle here, with the additional 
caveat that if one of the limitations is tickled that we issue a good 
diagnostic.

The current situation (gcc-5, gcc-6-rc) essentially de-optimizes 
protected systems in an attempt to work around the various limitations 
of protected symbols.  Reverting that change is, IMHO, what needs to 
happen.  My worry is that we're so damn late in the gcc-6 cycle that it 
may need to be deferred to 6.2 or beyond.

Jeff