Bug#328183: #328183: no-tls-direct-seg-refs
> > > will add a very little extra cost to single thread-specific variable
> > > accesses, but it shouldn't be noticeable at all.
> > Well, to be correct, switch -mno-tls-direct-seg-refs
> > add extra cost to ALL thread-specific variables accesses.
> No, only to isolated ones. The compiler can cache gs:0 (and it will do
> it anyway when -mno-tls-direct-seg-refs is not provided.
This is still more then single variable ...
Anyway, look at configure flags for basic libc in debian/sysdeps/i386.mk:
libc_extra_config_options = $(extra_config_options) --with-tls --without-__thread
It doesn't use TLS internally, there is no .tbss ot .tdata segment in libc.so.