[cfe-dev] solaris-specific mangling for g++ compat

[Fedor Sergeev via cfe-dev]

On Thu, Jul 13, 2017 at 01:34:24PM -0400, James Y Knight wrote:
> So, uh, why did solaris's stdlib.h header move these four types in the first
> place? It sounds like there was some code in the system header that
> conditionally put them into either the global namespace, or into the std
> namespace, dependent on the value of __cplusplus, yet all C++ compilers ever
> used on solaris were setting __cplusplus to the version where they were in the
> global namespace.
> So...I'm rather confused, then, as to why this mangling change was made in gcc
> in the first place, instead of just modifying the system header to not do
> that. Surely it'd have been saner to move the definitions back to the global
> namespace unconditionally? (And, I think that could even still be done?)

I really have no idea on what the full story was.
Probably Rainer can shed some light as he was quite involved in that discussion
(see https://gcc.gnu.org/ml/gcc-patches/2011-08/msg00834.html)

I was rather surprised to learn about this strange solution
when I hit it with Oracle Studio compiler couple years ago.

> For comparison, on linux glibc, tm, div_t, ldiv_t, and lconv are all just
> defined in :: and imported into std:: with using...

I'm going to ask around in Solaris, but if we ever manage to fix it in future Solaris versions,
headers on older ones will still trigger this incompatibility. :(

regards,
  Fedor.

> 
> 
> On Thu, Jul 13, 2017 at 12:56 PM, Fedor Sergeev via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
> 
>     Greetings folks,
> 
>     I just filed a bug on clang mangling:
>       https://bugs.llvm.org/show_bug.cgi?id=33767
> 
>     which is not clang's bug per se, but rather a bug-incompatibility
>     with gcc on Solaris (more details in bug report).
> 
>     gcc deliberately chose to diverge from mangling as specified by C++ ABI
>     in order to keep binary compatibility
>     (see https://gcc.gnu.org/ml/gcc-patches/2011-08/msg00834.html
>      for discussion of that patch).
> 
>     When clang on Solaris links with libstdc++ this binary compatibility
>     issue kicks in.
> 
>     I wonder would the patch doing Solaris-only hack to the mangling
>     to maintain gcc binary compatibility be welcome here?
>     Unconditionally or under some flag?
> 
>     regards,
>       Fedor.
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