[Bug target/58066] GCC mis-compiles access to TLS variable with -fPIC on x86_64

[ppluzhnikov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58066

--- Comment #3 from Paul Pluzhnikov <ppluzhnikov at google dot com> ---
(In reply to Paul Pluzhnikov from comment #2)

> What is the way to turn it on?

Compiling test case with -mtls-dialect=gnu2 does appear to improve the picture:

g++ -fPIC -O2 -S t.cc -mtls-dialect=gnu2

__cxa_get_globals:
        leaq    _ZL3ccc@TLSDESC(%rip), %rax
        call    *_ZL3ccc@TLSCALL(%rax)
        addq    %fs:0, %rax
        ret

The indirect call goes to _dl_tlsdesc_dynamic in ld-linux-x86-64.so.2 with
misaligned stack, and the latter re-aligns it.