[WebAssembly] WASI support for libcxx

[sunfish]

Summary

This adds explicit support for the WASI platform to libcxx. Notes:

• WASI libc uses some components from musl, however it's not fully compatible with musl, and this patch will allow us to stop using _LIBCPP_HAS_MUSL_LIBC and customize for WASI libc specifically.
• in src/random.cpp, getentropy is declared in <unistd.h> on all platforms I've checked (such as OpenBSD which had it first) except Darwin.

[sbc100]

src/thread.cpp

28

Does WASI not define __CloudABI__?

[ldionne]

src/random.cpp

28 ↗

(On Diff #197423)

If Fuchsia also needs this change, how come is the code working right now? I'm trying to understand the reason for this change.

[sunfish]

src/random.cpp

28 ↗

(On Diff #197423)

Some systems declare getentropy in both sys/random.h and unistd.h (eg. GLIBC), some just in unistd.h (eg. musl), and some just in sys/random.h (eg. Darwin). Perhaps Fuchsia is in the last category -- just in sys/random.h.

It looks like a better solution here is to just make WASI libc declare getentropy in its sys/random.h, so that we don't need to change the code here. I'll update the patch here accordingly.

[sunfish]

Drop the getentropy header file change from this patch.

[sunfish]

src/thread.cpp

28

No, WASI doesn't define CloudABI. It's derived from CloudABI, but contains numerous differences, so we felt it was best to not claim to be CloudABI to avoid confusion.

[ldionne]

I don't have any objection about this patch (but I also can't test that it works).

include/__config

 #endif // __sun__
 
 #if defined(__CloudABI__)
    // Certain architectures provide arc4random(). Prefer using
    // arc4random() over /dev/{u,}random to make it possible to obtain
    // random data even when using sandboxing mechanisms such as chroots,
    // Capsicum, etc.
 #  define _LIBCPP_USING_ARC4_RANDOM
-#elif defined(__Fuchsia__)
+#elif defined(__Fuchsia__) || defined(__wasi__)
 #  define _LIBCPP_USING_GETENTROPY
 #elif defined(__native_client__)
    // NaCl's sandbox (which PNaCl also runs in) doesn't allow filesystem access,
    // including accesses to the special files under /dev. C++11's
    // std::random_device is instead exposed through a NaCl syscall.
 #  define _LIBCPP_USING_NACL_RANDOM
 #elif defined(_LIBCPP_WIN32API)
 #  define _LIBCPP_USING_WIN32_RANDOM

 #else
 #  define _LIBCPP_NO_CFI
 #endif
 
 #if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L
 #  if defined(__FreeBSD__)
 #    define _LIBCPP_HAS_QUICK_EXIT
 #    define _LIBCPP_HAS_C11_FEATURES
-#  elif defined(__Fuchsia__)
+#  elif defined(__Fuchsia__) || defined(__wasi__)
 #    define _LIBCPP_HAS_QUICK_EXIT
 #    define _LIBCPP_HAS_TIMESPEC_GET
 #    define _LIBCPP_HAS_C11_FEATURES
 #  elif defined(__linux__)
 #    if !defined(_LIBCPP_HAS_MUSL_LIBC)
 #      if _LIBCPP_GLIBC_PREREQ(2, 15) || defined(__BIONIC__)
 #        define _LIBCPP_HAS_QUICK_EXIT
 #      endif

 
 // Thread API
 #if !defined(_LIBCPP_HAS_NO_THREADS) && \
     !defined(_LIBCPP_HAS_THREAD_API_PTHREAD) && \
     !defined(_LIBCPP_HAS_THREAD_API_WIN32) && \
     !defined(_LIBCPP_HAS_THREAD_API_EXTERNAL)
 #  if defined(__FreeBSD__) || \
       defined(__Fuchsia__) || \
+      defined(__wasi__) || \
       defined(__NetBSD__) || \
       defined(__linux__) || \
       defined(__GNU__) || \
       defined(__APPLE__) || \
       defined(__CloudABI__) || \
       defined(__sun__) || \
       (defined(__MINGW32__) && __has_include(<pthread.h>))
 #    define _LIBCPP_HAS_THREAD_API_PTHREAD

 // CloudABI is intended for running networked services. Processes do not
 // have standard input and output channels.
 #ifdef __CloudABI__
 #define _LIBCPP_HAS_NO_STDIN
 #define _LIBCPP_HAS_NO_STDOUT
 #endif
 
 #if defined(__BIONIC__) || defined(__CloudABI__) ||                            \
-    defined(__Fuchsia__) || defined(_LIBCPP_HAS_MUSL_LIBC)
+    defined(__Fuchsia__) || defined(__wasi__) || defined(_LIBCPP_HAS_MUSL_LIBC)
 #define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE
 #endif
 
 // Thread-unsafe functions such as strtok() and localtime()
 // are not available.
 #ifdef __CloudABI__
 #define _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 #endif

include/__locale

 # include <support/solaris/xlocale.h>
 #elif defined(_NEWLIB_VERSION)
 # include <support/newlib/xlocale.h>
 #elif (defined(__APPLE__)      || defined(__FreeBSD__) \
     || defined(__EMSCRIPTEN__) || defined(__IBMCPP__))
 # include <xlocale.h>
 #elif defined(__Fuchsia__)
 # include <support/fuchsia/xlocale.h>
+#elif defined(__wasi__)
+// WASI libc uses musl's locales support.
+# include <support/musl/xlocale.h>
 #elif defined(_LIBCPP_HAS_MUSL_LIBC)
 # include <support/musl/xlocale.h>
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 

src/include/config_elast.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(__wasi__)
+// No _LIBCPP_ELAST needed on WASI
 #elif defined(__linux__) || defined(_LIBCPP_HAS_MUSL_LIBC)
 #define _LIBCPP_ELAST 4095
 #elif defined(__APPLE__)
 // No _LIBCPP_ELAST needed on Apple
 #elif defined(__sun__)
 #define _LIBCPP_ELAST ESTALE
 #elif defined(_LIBCPP_MSVCRT_LIKE)
 #define _LIBCPP_ELAST (_sys_nerr - 1)
 #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

src/thread.cpp

 
 #if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
 # include <sys/param.h>
 # if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__) || defined(__APPLE__)
 #   include <sys/sysctl.h>
 # endif
 #endif // defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
 
-#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__) || defined(__Fuchsia__)
+#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__) || defined(__Fuchsia__) || defined(__wasi__)
 # include <unistd.h>
-#endif // defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__) || defined(__Fuchsia__)
+#endif // defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__) || defined(__Fuchsia__) || defined(__wasi__)
 
 #if defined(__NetBSD__)
 #pragma weak pthread_create // Do not create libpthread dependency
 #endif
 
 #if defined(_LIBCPP_WIN32API)
 #include <windows.h>
 #endif

test/support/test_macros.h

 // Sniff out to see if the underling C library has C11 features
 // Note that at this time (July 2018), MacOS X and iOS do NOT.
 // This is cribbed from __config; but lives here as well because we can't assume libc++
 #if __ISO_C_VISIBLE >= 2011 || TEST_STD_VER >= 11
 #  if defined(__FreeBSD__)
 //  Specifically, FreeBSD does NOT have timespec_get, even though they have all
 //  the rest of C11 - this is PR#38495
 #    define TEST_HAS_C11_FEATURES
-#  elif defined(__Fuchsia__)
+#  elif defined(__Fuchsia__) || defined(__wasi__)
 #    define TEST_HAS_C11_FEATURES
 #    define TEST_HAS_TIMESPEC_GET
 #  elif defined(__linux__)
 // This block preserves the old behavior used by include/__config:
 // _LIBCPP_GLIBC_PREREQ would be defined to 0 if __GLIBC_PREREQ was not
 // available. The configuration here may be too vague though, as Bionic, uClibc,
 // newlib, etc may all support these features but need to be configured.
 #    if defined(TEST_GLIBC_PREREQ)