[cfe-dev] libcxx error: template with C linkage
Alan Carvalho de Assis via cfe-dev
cfe-dev at lists.llvm.org
Thu Aug 23 13:02:07 PDT 2018
Today (almost two years later) I received an email from Anthony
Merlino, he discovered the source of the issue:
"The arm-gcc toolchain automatically wraps extern C around all headers
included using the -isystem path.
See: https://bugs.launchpad.net/gcc-arm-embedded/+bug/1698539
Another discussion: https://gcc.gnu.org/ml/gcc-help/2011-09/msg00158.html
This default behavior can be changed by setting NO_IMPLICIT_EXTERN_C
and rebuilding the toolchain. Working on that now so I can test and
make sure it works."
I decided to send it here because other people could face similar
issues and could to spend much time trying to find an unbalanced
"extern C" that in fact doesn't exist.
BR,
Alan
On 11/14/16, Alan Carvalho de Assis <acassis at gmail.com> wrote:
> 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
>>>>>
>>>>
>>>>
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>>>>
>>>>
>>>
>>
>
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