[cfe-dev] Latest clang and dllimport

[Yaron Keren]

The error reported is with mingw 5.1.0 which is failry new.
Maybe previous clangs were ok using previous versions of the mingw-w64
headers?


2015-07-22 0:39 GMT+03:00 Hans Wennborg <hans at chromium.org>:

> Hi Edward,
>
> I'm using this code to reproduce the issue you're seeing:
>
>   extern "C" void sleep(unsigned ms);
>   void f() {
>     sleep(1000);
>   }
>   extern "C" __declspec(dllimport) void sleep(unsigned ms);
>
> Compiling with "clang -target i686-pc-win32 -c a.cc" produces the
> error you describe.
>
> This produces an error both with both 3.5, 3.6 and trunk for me. Is it
> possible that something has changed in your code, or that something is
> getting #ifdef'ed differently based on the clang version?
>
> The problem here is that Clang doesn't want to change the
> "dllimport"-ness of sleep() after it has been called. If you try to
> add the dllimport attribute before sleep() has been used, Clang will
> just warn.
>
>  - Hans
>
> On Tue, Jul 21, 2015 at 12:36 PM, Edward Diener
> <eldlistmailingz at tropicsoft.com> wrote:
> > In the latest clang built from source, if a function is mismatched as to
> a
> > difference in dllimport attributes clang produces an error. As in:
> >
> >
> C:\Utilities\mingw-w64\i686-5.1.0-posix-dwarf-rt_v4-rev0\mingw32\i686-w64-mingw32\include\synchapi.h:127:26:
> > error: redeclaration of 'Sleep' cannot add 'dllimport' attribute
> >   WINBASEAPI VOID WINAPI Sleep (DWORD dwMilliseconds);
> >                          ^
> > ..\..\..\boost/smart_ptr/detail/yield_k.hpp:67:29: note: previous
> > declaration is here
> >   extern "C" void __stdcall Sleep( unsigned long ms );
> >
> > Changing the latter to:
> >
> >   extern "C" __declspec(dllimport) void __stdcall Sleep( unsigned long
> ms );
> >
> > fixes the problem for clang.
> >
> > Earlier versions of clang ( 3.4.1, 3.5.2, 3.6.1 ) did not have this
> problem.
> > Is there a __has_feature or __has_extension that I can use to test this
> > change in the latest clang ? The previous versions are also happy with
> the
> > __declspec(dllimport) added in the declaration so even without a
> > __has_feature or __has_extension I can just test for clang on Windows,
> but I
> > like to be as precise as possible in Boost code.
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