Remove add-ons mechanism

[Florian Weimer]

On 09/29/2017 12:01 AM, Zack Weinberg wrote:
> On Thu, Sep 28, 2017 at 1:49 PM, Joseph Myers <joseph@codesourcery.com> wrote:
>>
>> Add-ons involve significant, little-used complexity in the glibc build
>> system, and make it hard to understand what the space of possible
>> glibc configurations is.  This patch removes the add-ons mechanism.
> 
> I don't disagree with this patch exactly, but I was thinking of using
> the add-ons mechanism to prototype a CSPRNG addition to glibc

I've got something towards an implementation of arc4random (not 
certifiable, but it should be unpredictable in practice).

I think I found a way to do full fork protection even without 
MADV_WIPEONFORK, using a global counter in a MAP_SHARED segment. 
Reseeding is still needed to deal with a counter overflow on 32-bit 
architectures, and there is some overhead by the globally shared 
counter, but I think it is superior to all approaches I've seen so far 
(and it does not require a fork handler or a system call for every 
random number generation).

Thanks,
Florian