Add __no_instrument_function__ to _LIBCPP_INLINE_VISIBILITY and _LIBCPP_ALWAYS_INLINE

[mdaniels]

Summary

When using libc++ along with -finstrument-functions I am seeing link errors, even in the simple hello world case.

It looks like this is caused by functions in libc++'s headers that are marked to always be inlined. Since they are always inlined there is external definition for the linker to get the address of. I have worked around this by adding the no_instrument_function attribute to _LIBCPP_INLINE_VISIBILITY and _LIBCPP_ALWAYS_INLINE.

It looks like this was report with PR17879 but author closed it as invalid. So I could very well be missing something here.

Patch tested by running the test suite with -finstrument-functions set in the compiler flags. Link errors were no longer seen and there was no change to the test result when compared to a clean run. The tests were run using a x86_64 Linux host using gcc 5.4 and clang 3.8 with libc++ from ToT, as well as a QNX Neutrino host using gcc 5.4 and libc++ 3.7.

This may also be a problem on Windows as they has similar attributes being set, but I do not have a setup to test that.

[EricWF]

Could you please point me to the documentation regarding -finstrument-function?

[mdaniels]

You should be able to find it here, near the bottom: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html

[EricWF]

It looks like this is caused by functions in libc++'s headers that are marked to always be inlined. Since they are always inlined there is external definition for the linker to get the address of. I have worked around this by adding the no_instrument_function attribute to _LIBCPP_INLINE_VISIBILITY and _LIBCPP_ALWAYS_INLINE.

That isn't quite correct. This problem only occurs on methods which are externally instantiated withing the dylib but there definitions are marked __attribute__((visibility("hidden"))).
For example std::string and std::num_get. Therefore the compiler *knows* there is an externally available definition but its hidden from the linker.

I would prefer to fix this by using _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY on these methods instead of _LIBCPP_INLINE_VISIBILITY or _LIBCPP_ALWAYS_INLINE instead.

[EricWF]

I created a fix as described above. Could you please tell me if it works for you?

It can be found here:

https://reviews.llvm.org/D26324

include/__config

 #  endif
 #endif
 
 #ifndef _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS
 #  define _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS
 #endif
 
 #ifndef _LIBCPP_INLINE_VISIBILITY
-#define _LIBCPP_INLINE_VISIBILITY __attribute__ ((__visibility__("hidden"), __always_inline__))
+#define _LIBCPP_INLINE_VISIBILITY __attribute__ ((__visibility__("hidden"), __always_inline__,  __no_instrument_function__))
 #endif
 
 #ifndef _LIBCPP_ALWAYS_INLINE
-#define _LIBCPP_ALWAYS_INLINE  __attribute__ ((__visibility__("hidden"), __always_inline__))
+#define _LIBCPP_ALWAYS_INLINE  __attribute__ ((__visibility__("hidden"), __always_inline__, __no_instrument_function__))
 #endif
 
 #ifndef _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY
 # ifdef _LIBCPP_BUILDING_LIBRARY
 #   define _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY __attribute__((__visibility__("default"), __always_inline__))
 # else
 #   define _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY _LIBCPP_INLINE_VISIBILITY
 # endif