[llvm-dev] How to resolve conflicts between sanitizer_common and system headers

Dmitry Vyukov via llvm-dev
Fri, 01 Jul 2016 19:10:22 -0000

On Fri, Jul 1, 2016 at 8:53 PM, Anna Zaks <ganna at apple.com>
wrote:
> Hi Sanitizer Runtime Developers,
>
> We recently ran into a problem building clang because some of the
> definitions in sanitizer_common conflicted with system definitions and
later
> another system header was trying to use the system definition:
>
> .../usr/include/libkern/OSAtomicDeprecated.h:756:17: error: reference to
> 'memory_order_relaxed' is ambiguous
> __theAmount, memory_order_relaxed) + __theAmount);
> ^
> .../usr/bin/../include/c++/v1/atomic:548:5: note: candidate found by name
> lookup is 'std::__1::memory_order::memory_order_relaxed'
> memory_order_relaxed, memory_order_consume, memory_order_acquire,
> ^
>
../src/projects/compiler-rt/lib/tsan/../sanitizer_common/sanitizer_atomic.h:22:3:
> note: candidate found by name lookup is
> '__sanitizer::memory_order::memory_order_relaxed'
> memory_order_relaxed = 1 << 0,
> ^
>
>
> The problem is due to the combination of the following:
>  1. The runtime includes the system headers after the project headers (as
> per LLVM coding guidelines).
>  2. lib/sanitizer_common/sanitizer_internal_defs.h pollutes the namespace
of
> everything defined after it, which is all/most of the sanitizer .h and .cc
> files and the included system headers with:
>     using namespace __sanitizer;  // NOLINT
>  3. These are the definitions that conflict in this particular case, but
> this problem could reoccur in the future with other symbols as well:
>
> enum memory_order {
>   memory_order_relaxed = 1 << 0,
>   memory_order_consume = 1 << 1,
>   memory_order_acquire = 1 << 2,
>   memory_order_release = 1 << 3,
>   memory_order_acq_rel = 1 << 4,
>   memory_order_seq_cst = 1 << 5
> };
>
>
> We currently have a workaround (in the system header) that makes this
> non-blocking, but it would be good to cleanly address this problem.
Removing
> the "using namespace" from the header seems like the cleanest
solution.
> WDYT?
>
> Thanks,
> Anna.


Hi Anna,

What does OSAtomicDeprecated.h do? Does it also pull
memory_order_relaxed into global namespace?

For this particular problem we could just rename sanitizer internal constants.

Maybe doing something like "namespace __tsan { using namespace
__sanitizer_common; }" will help to resolve it in general case. But I
am not sure, need to know what system headers do.