[Bug target/113874] GNU2 TLS descriptor calls do not follow psABI on x86_64-linux-gnu

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113874

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
E.g.
https://sourceware.org/legacy-ml/binutils/2005-09/msg00184.html
says
The functions defined above use custom calling conventions that
require them to preserve any registers they modify.  This penalizes
the case that requires dynamic TLS, since it must preserve all
call-clobbered registers before calling __tls_get_addr(), but it is
optimized for the most common case of static TLS, and also for the
case in which the code generated by the compiler can be relaxed by the
linker to a more efficient access model: being able to assume no
registers are clobbered by the call tends to improve register
allocation.  Also, the function that handles the dynamic TLS case will
most often be able to avoid calling __tls_get_addr(), thus potentially
avoiding the need for preserving registers.