[PATCH] Reserve static TLS for dynamically loaded initial-exec TLS only [BZ #25051]

[Florian Weimer]

* Carlos O'Donell:

> Let me take a stab at this:
>
> (1) File a bug to indicate all libraries must stop using
>     TLS IE to fix dlmopen issues with TLS IE.

Do you mean glibc components, or do you view this as a distribution-wide
change?

> (2) Set DL_NNS to 4, and add a tunable that lets you change
>     the limit to reduce surplus memory allocated.
>
>     (2.a) send linux man-pages a patch to make dlmopen(3)
>     ambiguous about how many namespaces are supported and
>     to point at the tunable to increase the memory used.
>
> (3) I think that the surplus should be split into two
>     blocks:
>     (3.a) Some reserved for TLS IE libs.
>     (3.b) Some reserved for tlsdesc optimization.
>
>     My opinion is that any library that is loaded and
>     needs TLS IE should be able to use (3.a). We should
>     reserve enough for (3.a) to be able to load glibc
>     libraries, libgomp, and libgl (as you note).

There's also a potential for not letting audit libraries consume
namespace slots (once they are dynamic).  This will enable lower DL_NNS
defaults.

Thanks,
Florian