[LLVMdev] 3.4 branch gcc 4.9 build error

[Alp Toker]

On 05/05/2014 20:51, Richard Smith wrote:
> On Mon, May 5, 2014 at 10:47 AM, Chandler Carruth 
> <chandlerc at google.com <mailto:chandlerc at google.com>> wrote:
>
>     On Mon, May 5, 2014 at 8:11 AM, Alp Toker <alp at nuanti.com
>     <mailto:alp at nuanti.com>> wrote:
>
>         I suspect that pulling in clang header fixes r201729, r202911
>         and r207606 to 3.4.1 will resolve libstdc++ / glibc
>         compatibility issues people have been having with 3.4:
>
>           r201729: Teach Clang to provide ::max_align_t in C11 and
>         C++11 modes)
>           r202911: Headers: Provide an ABI compatible max_align_t when
>         _MSC_VER is defined)
>           r207606: Let stddef.h respect __need_{wchar_t, size_t, NULL,
>         ptrdiff_t, wint_t}.
>
>         The changes look safe to merge but I'd like to hear a second
>         opinion from Chandler or Nico.
>
>
>     I believe all of these are very safe, but I respect Tom's position
>     here. As he is managing the release, he gets to say "not in this
>     one". If you want someone to approve merging these three patches
>     into any release, Richard Smith is the person to ask IMO.
>
>
> The first two are approved for the branch if Tom wants to take them 
> (and they seem like good fixes to have).
>
> Tom: if you take r201729, you will need to also take the corresponding 
> libc++ change, r201843.
>
> r207606 hasn't had much time to bake, and fixes a problem that is not 
> a regression, so I'd be hesitant to approve it for 3.4.1.

Thanks for pointing that out Richard. r201729 + r201843 sounds good.

I'm concerned that advice has already appeared online instructing users 
to patch their libstdc++ system headers in order to install clang 3.4 on 
Linux. If we don't get the right fix out, distributors will find their 
own way to ship 3.4.1 to the detriment of our users and against our own 
interests.

   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=744792 - clang-3.4: 
unusable with libstdc++ from gcc 4.9
   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=744872 - once 
gcc-4.9 and g++-4.9 are installed, clang stops properly building 
existing projects
   https://bugzilla.redhat.com/show_bug.cgi?id=1092622 - clang-3.4: 
unusable with libstdc++ from gcc 4.9

Alp.

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