[cfe-dev] libcxx error: template with C linkage

Alan Carvalho de Assis via cfe-dev cfe-dev at lists.llvm.org
Mon Nov 14 10:34:44 PST 2016 

Hi Richard,

Right, please find it attached.

Just to recall, these are the errors:

make[1]: Entering directory '/tmp/LIBCXX/nuttx_libcxx/libxx'
CXX:  libcxx/algorithm.cxx
arm-none-eabi-g++ -c  -Wall -Wshadow -Wundef -Os -fno-strict-aliasing
-fno-strength-reduce -fomit-frame-pointer -mcpu=cortex-m4 -mthumb
-mfloat-abi=soft -I. -isystem /tmp/LIBCXX/nuttx_libcxx/include
-isystem /tmp/LIBCXX/nuttx_libcxx/include/cxx -isystem
/tmp/LIBCXX/nuttx_libcxx/include/libcxx   -pipe -std=c++11
-DCLOCK_MONOTONIC -D__NuttX__ -fno-builtin -fno-exceptions -fcheck-new
-fno-rtti -pedantic -D_DEBUG -D_LIBCPP_BUILD_STATIC
-D_LIBCPP_NO_EXCEPTIONS  libcxx/algorithm.cxx -o  algorithm.o
In file included from /tmp/LIBCXX/nuttx_libcxx/include/libcxx/algorithm:636:0,
                 from libcxx/algorithm.cxx:10:
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/initializer_list:58:1: error:
template with C linkage
 template<class _Ep>
 ^
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/initializer_list:96:1: error:
template with C linkage
 template<class _Ep>
 ^
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/initializer_list:105:1: error:
template with C linkage
 template<class _Ep>
 ^
In file included from /tmp/LIBCXX/nuttx_libcxx/include/libcxx/algorithm:637:0,
                 from libcxx/algorithm.cxx:10:
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/type_traits:395:1: error:
template with C linkage
 template <class _T1, class _T2> struct _LIBCPP_TYPE_VIS_ONLY pair;
 ^
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/type_traits:396:1: error:
template with C linkage
 template <class _Tp> class _LIBCPP_TYPE_VIS_ONLY reference_wrapper;
 ^
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/type_traits:397:1: error:
template with C linkage
 template <class _Tp> struct _LIBCPP_TYPE_VIS_ONLY hash;
 ^
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/type_traits:399:1: error:
template with C linkage
 template <class>
 ^
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/type_traits:402:1: error:
template with C linkage
 template <class _Tp>
 ^
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/type_traits:405:1: error:
template with C linkage
 template <class _Tp, bool>
 ^
/tmp/LIBCXX/nuttx_libcxx/include/libcxx/type_traits:408:1: error:
template with C linkage


BR,

Alan

On 11/14/16, Richard Smith <richard at metafoo.co.uk> wrote:
> On 14 Nov 2016 3:13 am, "Alan Carvalho de Assis" <acassis at gmail.com> wrote:
>
> Thank you Eric and Richard,
>
> Yes, I think there is some 'export "C" { ' without the closing brace
> '}' in some NuttX header.
>
> I got libcxx working on NuttX. Basically all I needed to do was to add
> 'extern "C++" {' inside all headers files:
>
> https://bitbucket.org/acassis/libcxx/commits/all
>
> Should these modification be included on libcxx? I can submit my patches!
>
>
> Not until we understand the problem. Can you provide the preprocessed
> source as requested?
>
> BR,
>
> Alan
>
> On 11/14/16, Eric Fiselier <eric at efcs.ca> wrote:
>> On Sun, Nov 13, 2016 at 7:12 PM, Richard Smith <richard at metafoo.co.uk>
>> wrote:
>>
>>> On 13 Nov 2016 5:27 pm, "Eric Fiselier via cfe-dev" <
>>> cfe-dev at lists.llvm.org> wrote:
>>>
>>> > But I used -save-temps to create the algorithm.ii and searched for all
>>> > occurrences of 'extern "C" {' inside it and I can confirm there is not
>>> > C++ header inside any 'extern C' block.
>>>
>>> Are you sure about that? libc++ provides its own version of each C
>>> library
>>> header as well (ex. <math.h>).
>>> My best guess is that the system C library is included a libc++ C
>>> library
>>> wrapper inside an 'extern C' block.
>>>
>>>
>>> Don't libc++'s .h headers all have an extern "C++" block to avoid that
>>> possibility?
>>>
>>
>> It seems some headers do, including <math.h>, but there are still others
>> without it.
>>
>>
>>
>>>
>>> There also doesn't seem to be any evidence of this in the #include stack
>>> reported by the compiler. It looks like maybe a system header ended with
>>> an
>>> extern "C" still open, or somehow libc++'s headers are being implicitly
>>> treated as "extern C" system headers (which get an explicit extern "C"
>>> wrapped around them).
>>>
>>> Alan, can you provide the preprocessed file produced by -save-temps?
>>>
>>> /Eric
>>>
>>>
>>> On Mon, Nov 7, 2016 at 10:17 AM, Alan Carvalho de Assis via cfe-dev <
>>> cfe-dev at lists.llvm.org> wrote:
>>>
>>>> Hi Everyone,
>>>>
>>>> I'm compiling the LLVM libcxx for NuttX RTOS (compiling on Linux to
>>>> integrate it on NuttX).
>>>>
>>>> But it is failing with tons of these "error: template with C linkage" :
>>>>
>>>> make[1]: Entering directory '/home/alan/nuttxspace/nuttx/libxx'
>>>> CXX:  libcxx/algorithm.cxx
>>>> arm-none-eabi-g++ -c  -Wall -Wshadow -Wundef -g -mcpu=cortex-m4
>>>> -mthumb -mfloat-abi=soft -I. -isystem
>>>> /home/alan/nuttxspace/nuttx/include -isystem
>>>> /home/alan/nuttxspace/nuttx/include/cxx -isystem
>>>> /home/alan/nuttxspace/nuttx/include/libcxx   -pipe -std=c++11
>>>> -DCLOCK_MONOTONIC -D__NuttX__ -pedantic -D_DEBUG
>>>> -D_LIBCPP_BUILD_STATIC  libcxx/algorithm.cxx -o  algorithm.o
>>>> In file included from
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/algorithm:639:0,
>>>>                  from libcxx/algorithm.cxx:10:
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:397:1: error:
>>>> template with C linkage
>>>>  template <class _T1, class _T2> struct _LIBCPP_TYPE_VIS_ONLY pair;
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:398:1: error:
>>>> template with C linkage
>>>>  template <class _Tp> class _LIBCPP_TYPE_VIS_ONLY reference_wrapper;
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:399:1: error:
>>>> template with C linkage
>>>>  template <class _Tp> struct _LIBCPP_TYPE_VIS_ONLY hash;
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:401:1: error:
>>>> template with C linkage
>>>>  template <class>
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:404:1: error:
>>>> template with C linkage
>>>>  template <class _Tp>
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:407:1: error:
>>>> template with C linkage
>>>>  template <class _Tp, bool>
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:410:1: error:
>>>> template with C linkage
>>>>  template <bool _Bp, class _If, class _Then>
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:412:1: error:
>>>> template with C linkage
>>>>  template <class _If, class _Then>
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:419:1: error:
>>>> template with C linkage
>>>>  template <bool, class _Tp> struct _LIBCPP_TYPE_VIS_ONLY
>>>> __lazy_enable_if
>>>> {};
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:420:1: error:
>>>> template with C linkage
>>>>  template <class _Tp> struct _LIBCPP_TYPE_VIS_ONLY
>>>> __lazy_enable_if<true, _Tp> {typedef typename _Tp::type type;};
>>>>  ^
>>>> /home/alan/nuttxspace/nuttx/include/libcxx/type_traits:422:1: error:
>>>> template with C linkage
>>>>  template <bool, class _Tp = void> struct _LIBCPP_TYPE_VIS_ONLY
>>>> enable_if
>>>> {};
>>>>
>>>>
>>>>
>>>>
>>>> I searched on Internet and discovered that this error happens when
>>>> there is some 'extern "C" { ' without the closing ' }' and then it
>>>> wrap some C++ code.
>>>>
>>>> I saw this comment inside ctype.h :
>>>>
>>>> #ifdef __cplusplus
>>>> #if defined(_LIBCPP_MSVCRT)
>>>> // We support including .h headers inside 'extern "C"' contexts, so
>>>> switch
>>>> // back to C++ linkage before including these C++ headers.
>>>> extern "C++" {
>>>>   #include "support/win32/support.h"
>>>>   #include "support/win32/locale_win32.h"
>>>> }
>>>> #endif // _LIBCPP_MSVCRT
>>>>
>>>> Although I'm not on MSVCRT, the comment explains why this error could
>>>> happen.
>>>>
>>>> But I used -save-temps to create the algorithm.ii and searched for all
>>>> occurrences of 'extern "C" {' inside it and I can confirm there is not
>>>> C++ header inside any 'extern C' block.
>>>>
>>>> After many tests I noted that if I modify include/algorithm to include
>>>> 'extern "C++" {' :
>>>> @@ -634,7 +634,10 @@ template <class BidirectionalIterator, class
>>>> Compare>
>>>>
>>>>  #include <__config>
>>>>  #include <initializer_list>
>>>> +extern "C++"
>>>> +{
>>>>  #include <type_traits>
>>>> +}
>>>>  #include <cstring>
>>>>  #include <utility> // needed to provide swap_ranges.
>>>>  #include <memory>
>>>>
>>>> The issue disappear, but I want to discover the root caused instead of
>>>> use an ugly hack.
>>>>
>>>> How I can discover where the error is happening, since -save-temps
>>>> didn't show nothing wrong ?
>>>>
>>>> BR,
>>>>
>>>> Alan
>>>> _______________________________________________
>>>> cfe-dev mailing list
>>>> cfe-dev at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>
>>>
>>>
>>> _______________________________________________
>>> cfe-dev mailing list
>>> cfe-dev at lists.llvm.org
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>>>
>>>
>>>
>>
>
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