[cfe-dev] Why does Xcode define _LIBCPP_HAS_NO_ASAN when enabling address sanitizer?

[Sean McBride via cfe-dev]

On Mon, 8 Aug 2016 23:59:19 +0100, Jonathan Coe via cfe-dev said:

>Turning on address sanitizer in Xcode 7 passes the compile and linker flag
>-fsanitize=address and also defines _LIBCPP_HAS_NO_ASAN.
>
>When building my library from the command line and running tests on a
>sanitized build without defining _LIBCPP_HAS_NO_ASAN I see non-repeatable
>address-sanitizer-reported memory access issues. Defining
>_LIBCPP_HAS_NO_ASAN, as Xcode does, gets rid of the sanitizer issues but
>I'm curious as to why it needs doing.
>
>Why do I need to define _LIBCPP_HAS_NO_ASAN with AppleClang7 to avoid
>getting memory access issues in libcxx?

I believe it was as a result of this thread:
<http://lists.apple.com/archives/xcode-users/2016/Jan/msg00076.html>

That is: otherwise you'd get false positives if you linked to some C++ libs not themselves built with ASan.  As of Xcode 7.3 there is the CLANG_ADDRESS_SANITIZER_CONTAINER_OVERFLOW build option.

Cheers,

-- 
____________________________________________________________
Sean McBride, B. Eng                 sean at rogue-research.com
Rogue Research                        www.rogue-research.com 
Mac Software Developer              Montréal, Québec, Canada