[libcxx] type_info/bad_cast observations relating to r191397

G M gmisocpp at gmail.com
Wed Oct 2 07:10:15 PDT 2013

Hi Everyone
Change r191397 affected the libcxx test suite results on my
windows machine for g++ and mingw (and possibly eventually VS) builds.

The comment is:
"Make the guard for external ABI libraries include the guard for
 libsupc++ in typeinfo.cpp, bringing it into agreement with
exception.cpp. This fixes link errors due to duplicate symbols from
this translation unit."

I don't know that r191397 is wrong but after applying that change I noticed
some additional test suite failures. One example:

which now results in a linker error where it previously compiled. The
linker error is:
"undefined reference to std::bad_cast::bad_cast()"

Another test case may be similarly effected is:

Looking at the change, it's because libcxx/src/type_info.cpp was changed
from this:
#if !(defined(_LIBCPPABI_VERSION) || defined(LIBCXXRT))

to this:
#if !defined(LIBCXXRT) && !defined(_LIBCPPABI_VERSION) &&

and on my builds this now blocks out the definitions for bad_cast and
type_info constructors etc. This would account for the linker error, as on
my machine LIBCXXRT is not defined && LIBCPPABI_VERSION is not defined

A grep of _LIBCPPABI_VERSION in the libcxx code base shows a few references
to other code that may be of interest here.
My machine has cxxabi.h which appears possibly also of interest.
Does anyone know what should be linked in to the above mentioned test cases
to restore the bad_cast and type_info definitions for g++/mingw/vs if they
are not to be provided by libcxx, so as to make the libcxx test cases
compile again?

Alternatively if r191397 is incorrect / insufficient, what should be
changed in libcxx or the changed guard mentioned above, that will re-enable
libcxx to again provide these definitions if it should?

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