[libcxx] Add support for Fuchsia

[phosek]

Summary

Fuchsia is a new operating system which uses libc++ and libc++abi as the C++ standard library.

[EricWF]

Is this *all* that's needed to get libc++ working?

[phosek]

Currently yes, we've been using libc++ (and libc++abi which doesn't need any changes) for a few months now without any problems. Our C library is a fork of musl so we rely on all the changes that have already been done to support it. However, we're building libc++ with LIBCXX_HAS_MUSL_LIBC=ON but we're slowly diverging from the upstream version so it might be better to stop relying on that option. I'd have to copy include/support/musl/xlocale.h to include/support/fuchsia/xlocale.h. Would that be fine with you?

[EricWF]

Cool! This patch LGTM then.

we're slowly diverging from the upstream version so it might be better to stop relying on that option. I'd have to copy include/support/musl/xlocale.h to include/support/fuchsia/xlocale.h. Would that be fine with you?

That sounds fine.

[EricWF]

PS. If your not already locked into an ABI you'll want to look into enabling the most recent ABI breaking changes. See the _LIBCPP_ABI_VERSION configuration at the top of __config for more info.

[phosek]

That sounds fine.

Shall I send it as a separate patch or update this one?

PS. If your not already locked into an ABI you'll want to look into enabling the most recent ABI breaking changes. See the _LIBCPP_ABI_VERSION configuration at the top of __config for more info.

We're already defaulting to LIBCXX_ABI_VERSION=2, I figured that's what we want to be using.

[EricWF]

In D25414#565956, @phosek wrote:

That sounds fine.

Shall I send it as a separate patch or update this one?

I would send a separate patch. This one is already good to go so you might as well commit it.

PS. If your not already locked into an ABI you'll want to look into enabling the most recent ABI breaking changes. See the _LIBCPP_ABI_VERSION configuration at the top of __config for more info.

We're already defaulting to LIBCXX_ABI_VERSION=2, I figured that's what we want to be using.

Great! Just be aware that ABI v2 is not yet stable. We're just staging it for later.

[mclow.lists]

@EricWF > Cool! This patch LGTM then.

This looks fine to me, too.

[Eugene.Zelenko]

Closed in rL283788.

include/__config

 #if !(__has_feature(cxx_variable_templates))
 #define _LIBCPP_HAS_NO_VARIABLE_TEMPLATES
 #endif
 
 #if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L
 #if defined(__FreeBSD__)
 #define _LIBCPP_HAS_QUICK_EXIT
 #define _LIBCPP_HAS_C11_FEATURES
+#elif defined(__Fuchsia__)
+#define _LIBCPP_HAS_QUICK_EXIT
+#define _LIBCPP_HAS_C11_FEATURES
 #elif defined(__linux__)
 #if !defined(_LIBCPP_HAS_MUSL_LIBC)
 #if __GLIBC_PREREQ(2, 15) || defined(__BIONIC__)
 #define _LIBCPP_HAS_QUICK_EXIT
 #endif
 #if __GLIBC_PREREQ(2, 17)
 #define _LIBCPP_HAS_C11_FEATURES
 #endif

 #  define _LIBCPP_WEAK __attribute__((__weak__))
 #endif
 
 // Thread API
 #if !defined(_LIBCPP_HAS_NO_THREADS) && \
     !defined(_LIBCPP_HAS_THREAD_API_PTHREAD) && \
     !defined(_LIBCPP_HAS_THREAD_API_EXTERNAL)
 # if defined(__FreeBSD__) || \
+    defined(__Fuchsia__) || \
     defined(__NetBSD__) || \
     defined(__linux__) || \
     defined(__APPLE__) || \
     defined(__CloudABI__) || \
     defined(__sun__)
 #  define _LIBCPP_HAS_THREAD_API_PTHREAD
 # else
 #  error "No thread API"

src/include/config_elast.h

 #else
 #include <errno.h>
 #endif
 
 #if defined(ELAST)
 #define _LIBCPP_ELAST ELAST
 #elif defined(_NEWLIB_VERSION)
 #define _LIBCPP_ELAST __ELASTERROR
+#elif defined(__Fuchsia__)
+// No _LIBCPP_ELAST needed on Fuchsia
 #elif defined(__linux__)
 #define _LIBCPP_ELAST 4095
 #elif defined(__APPLE__)
 // No _LIBCPP_ELAST needed on Apple
 #elif defined(__sun__)
 #define _LIBCPP_ELAST ESTALE
 #elif defined(_WIN32)
 #define _LIBCPP_ELAST _sys_nerr
 #else
 // Warn here so that the person doing the libcxx port has an easier time:
 #warning ELAST for this platform not yet implemented
 #endif
 
 #endif // _LIBCPP_CONFIG_ELAST