[Patch 4.6] In system.h, wrap include of C++ header in 'extern C++'

[Richard Guenther]

On Sat, Jun 16, 2012 at 8:47 PM, Gabriel Dos Reis
<gdr@integrable-solutions.net> wrote:
> On Sat, Jun 16, 2012 at 3:54 AM, Duncan Sands <baldrick@free.fr> wrote:
>> Hi,
>>
>>
>>>> If ENABLE_BUILD_WITH_CXX is defined, then GCC itself is built with C++,
>>>> and we want a C++ signature for functions.  If it is not defined, then
>>>> GCC itself is not built with C++, and we want (and must have) a C
>>>> signature.
>>>>
>>>> I suppose we would decide that fancy_abort always uses a C signature,
>>>> but that seems odd.
>>>>
>>>> Ian
>>>
>>>
>>> I guess the issue is when people care only about C plugins, yet
>>> fancy_abort
>>> get implicitly exported with a C++ linkage.
>>>
>>> I suspect this goes back to the eternal question: what do we consider as
>>> part of the public GCC public API (no, Basile, I am not suggesting to have
>>> the same discussion again.)
>>
>>
>> if the following are to hold
>>
>> (1) fancy_abort is declared in system.h
>> (2) system.h should not be wrapped in extern "C" when included from a
>> plugin,
>> (3) it should be valid to include it from plugins compiled as C or as C++,
>> (4) fancy_abort should use the same linkage as GCC, i.e. C when GCC built as
>> C,
>> C++ when built as C++ (aka ENABLE_BUILD_WITH_CXX).
>>
>> then something like the following seems inevitable:
>>
>> #ifdef ENABLE_BUILD_WITH_CXX
>> #ifdef __cplusplus
>> extern void fancy_abort(const char *, int, const char *) ATTRIBUTE_NORETURN;
>> #else
>> extern void _Z11fancy_abortPKciS0_(const char *, int, const char *)
>> ATTRIBUTE_NORETURN;
>> #endif
>> #else
>> #ifdef __cplusplus
>> extern "C" void fancy_abort(const char *, int, const char *)
>> ATTRIBUTE_NORETURN;
>> #else
>> extern void fancy_abort(const char *, int, const char *) ATTRIBUTE_NORETURN;
>> #endif
>> #endif
>>
>> That's pretty nasty.  But to avoid the nastiness one of (1) - (4) needs to
>> be
>> dropped.  Which one?
>>
>> Ciao, Duncan.
>
> It is not just nasty; it is fragile.
> I think we should just give fancy_abort a C language specification.

No, I think we should make system.h what system.h is about - include
all system headers.

declaring fancy_abort with either linkage is not part of "inlude
system headers" and thus
should not be done inside system.h.

Richard.