[Bug other/55354] [asan] by default, the asan run-time should be linked statically, not dynamically

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55354

--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-11-19 08:54:47 UTC ---
I bet 9.5% or more of that is due to the PLT call.  The thing is, even when you
have initial-exec TLS model code, if you link it into an executable and the
referenced TLS variable is in the executable, the linker TLS transitions
optimization changes the IE model into LE model, so instead of something like:
  mov    0x2009a9(%rip),%rax
  mov    %fs:(%rax),%eax
you'll end up with
  mov    $-4,%rax
  mov    %fs:(%rax),%eax
or so (compared to
  mov    %fs:-4,%eax
if it was local-exec model from the beginning).  Given the amount of code in
__tsan_read8, I seriously doubt it is noticeable.  So, please compare libtsan
built with -fPIC -ftls-model=initial-exec with libtsan built with -fPIE
(-ftls-model=local-exec).  The former will not require any special hacks and
will work just fine even with shared libraries, the latter won't.