[LLVMdev] 3.4 branch gcc 4.9 build error

[Tom Stellard]

On Mon, May 05, 2014 at 11:42:28PM +0100, Alp Toker wrote:
> 
> 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.
>

We can work with distros to make sure they apply the correct fix until
we can get them into a release.

It's just too late for these to go into 3.4.1.  The code has already
been validated and is ready to be released.  However, I have no problem with
doing a 3.4.2 release with these patches.  Pushing these off to the next
release will also give us a chance to fully test LLVM 3.4 with gcc 4.9,
so we will be able to include other fixes as necessary.

-Tom

>    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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