extend dl-minimal malloc implementation

[Florian Weimer]

On 08/11/2017 03:02 PM, Carlos O'Donell wrote:
> Then we could use the bootstrap arena with minimal support, and eventually
> free from it, and with correct accounting get 100% of it freed back to the
> OS and we could monitor this. We would never allocate from this arena, and
> we need not put it on the arena list / free list so it won't be used for
> future allocations.

If we never allocate from there, how would we achieve the goal of giving
back unneeded memory?

I also think that in the long term, we should separate ld.so data
structures from the rest of libc, and even try to map keep read-only
most of the time (when dlopen is not running).

Thanks,
Florian