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

["dvyukov at google dot com" <gcc-bugzilla@gcc.gnu.org>]

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

--- Comment #23 from Dmitry Vyukov <dvyukov at google dot com> 2012-11-23 07:27:27 UTC ---
(In reply to comment #21)
> (In reply to comment #20)
> > What I see is that it also affect code generation (register allocation). Do we
> > need to file a bug on that?
> 
> If you see a code generation difference even with -ftls-model=local-exec -fPIC
> vs. -fPIE, then it must mean you don't have visibility attributes on the
> symbols used in the fast path.  For initial-exec, the RA effects should be
> minimal, the TLS offset load from got is usually very close to the actual TLS
> memory load (or lea), and thus it will just pick up some short lived scratch
> register.  Generally in GCC, -fPIE sets flag_pic and not flag_shlib, while
> -fPIC sets flag_pic and flag_shlib.  flag_pic is about whether position
> independent code needs to be generated, flag_shlib is about whether locally
> defined symbols can be interposed (plus it affects TLS model default choice).

When I compile with -fvisibility=hidden, it does not affect generated code.
It's not that we access a lot of symbols in the function, there is one
thread-local and one static global var.

That "minimal" RA effects do have effect in our case. We don't have a reserve
to squeeze another register for tls access:

// -fPIE
000000000009ca30 <__tsan_write2>:
   9ca30:       64 48 8b 04 25 40 1f    mov    %fs:0xffffffffffeb1f40,%rax
   9ca37:       eb ff 
   9ca39:       48 8b 0c 24             mov    (%rsp),%rcx
   9ca3d:       a8 01                   test   $0x1,%al
   9ca3f:       0f 85 d3 00 00 00       jne    9cb18 <__tsan_write2+0xe8>
   9ca45:       48 83 e8 80             sub    $0xffffffffffffff80,%rax
   9ca49:       48 89 fe                mov    %rdi,%rsi
   9ca4c:       48 89 c2                mov    %rax,%rdx
   9ca4f:       64 48 89 04 25 40 1f    mov    %rax,%fs:0xffffffffffeb1f40
   9ca56:       eb ff 

// -fPIC -ftls-model=initial-exec
00000000000969f0 <__tsan_write2>:
   969f0:       48 c7 c2 40 1f eb ff    mov    $0xffffffffffeb1f40,%rdx
   969f7:       53                      push   %rbx
   969f8:       48 8b 4c 24 08          mov    0x8(%rsp),%rcx
   969fd:       64 48 8b 02             mov    %fs:(%rdx),%rax
   96a01:       a8 01                   test   $0x1,%al
   96a03:       0f 85 c7 00 00 00       jne    96ad0 <__tsan_write2+0xe0>