Add initial support for the MUSL C library.

[vkalintiris]

Summary

This patch adds the LIBCXX_LIBC_IS_MUSL cmake option to allow the
building of libcxx with the Musl C library. The option is necessary as
Musl does not provide any predefined macro in order to test for its
presence, like GLIBC. Most of the changes specify the correct path to
choose through the various #if/#else constructs in the locale code.

Depends on D13407.

[jroelofs]

LGTM, with one small nit (and once D13407 lands):

src/locale.cpp

1176 ↗

(On Diff #37169)

s/|| ||/||/

[jroelofs]

D13407 has landed.

[EricWF]

I don't think this is ready to go. Please don't commit yet. Sorry @jroelofs.

CMakeLists.txt

309 ↗

(On Diff #37169)

Please name the macro "_LIBCPP_HAS_MUSL_LIBC" for consistency.

include/__config

370 ↗

(On Diff #37169)

Where does the __GLIBC__ macro definition come from? I thought it came from the C library headers but we don't include any!

[jroelofs]

include/__config

370 ↗

(On Diff #37169)

No need for the check to look at GLIBC anyway... _LIBCXX_LIBC_IS_MUSL would be available here, so you should be testing for: !defined(_LIBCXX_LIBC_IS_MUSL) instead (or however that flag ends up being named).

include/support/musl/xlocale.h

10 ↗

(On Diff #37169)

This comment was cargo-culted from include/support/xlocale/xlocale.h... Given that this is musl-specific, I don't think it makes sense to call this file "shared" in the same sense that the other one is.

[EricWF]

include/__config

370 ↗

(On Diff #37169)

Sounds good to me.

[vkalintiris]

Address reviewers' comments.

[vkalintiris]

CMakeLists.txt

309 ↗

(On Diff #37169)

Should I rename the corresponding cmake option too?

[EricWF]

Thanks for the quick turn around. This patch is almost ready to land but still needs a couple more changes.

include/__config

387 ↗

(On Diff #37335)

#else // defined(_LIBCPP_HAS_MUSL_LIBC)

include/__config_site.in

21 ↗

(On Diff #37335)

No need for whitespace.

include/__locale

40 ↗

(On Diff #37335)

Since musl depends on support headers you should add a CMake check that ensures LIBCXX_INSTALL_SUPPORT_HEADERS is not turned off when LIBCXX_LIBC_IS_MUSL is ON.

include/support/musl/xlocale.h

21 ↗

(On Diff #37335)

It looks like this header uses more symbols than are just provided by cstdlib. Please add the required includes.

src/locale.cpp

958 ↗

(On Diff #37335)

Where did the __NetBSD__ case go?

[EricWF]

Thanks for the quick turn around. This patch is almost ready to land but still needs a couple more changes.

CMakeLists.txt

320 ↗

(On Diff #37335)

Yes please, I wasn't going to ask but I would prefer LIBCXX_HAS_MUSL_LIBC.

[vkalintiris]

Sorry for the delay.

Addressed reviewer comments and modifed CMake to check that
LIBCXX_INSTALL_SUPPORT_HEADERS is not turned off when LIBCXX_LIBC_IS_MUSL is ON.

[vkalintiris]

src/locale.cpp

958 ↗

(On Diff #37335)

It's in the previous #line directive, check line 956.

[EricWF]

Thanks for the update, I think this should be good to go. I'll give it a final once over tonight.

src/locale.cpp

958 ↗

(On Diff #37850)

Ah, sorry I missed that. So this was an existing bug. Thanks.

[vkalintiris]

In D13673#271518, @EricWF wrote:

Thanks for the update, I think this should be good to go. I'll give it a final once over tonight.

Ping.

[vkalintiris]

s/__NetBSD_\)/__NetBSD__\)/

[vkalintiris]

Ping.

[EricWF]

LGTM.

[vkalintiris]

Thanks for the review!

Everything seems fine from the buildbots except for a single test that failed:

http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-debian/builds/730

The next build (731) of that buildbot was green. Is libc++::try_lock_shared_for.pass.cpp a known flakey test?

[EricWF]

Yep. That's a flaky test. No need to worry.

[ldionne]

@vkalintiris @jroelofs Is it possible to detect Musl through some macro? I'd like to get rid of the CMake option -- this isn't the sort of property that we want to set explicitly at configure time, it's the sort of property we want to sniff out in the library instead.

[jroelofs]

In D13673#2394064, @ldionne wrote:

@vkalintiris @jroelofs Is it possible to detect Musl through some macro? I'd like to get rid of the CMake option -- this isn't the sort of property that we want to set explicitly at configure time, it's the sort of property we want to sniff out in the library instead.

I wish there was. Last I remember talking about it, Rich Felker was really against having one. I doubt this has changed.

[jroelofs]

More context: https://www.openwall.com/lists/musl/2013/03/29/13

[ldionne]

In D13673#2394187, @jroelofs wrote:

More context: https://www.openwall.com/lists/musl/2013/03/29/13

Thanks for the context. This is a very puristic point of view from the musl author.. not very useful. There are things that are difficult to detect with a check like __has_feature or similar, and having a macro to detect the library is necessary.

libcxx/trunk/CMakeLists.txt

 option(LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE "Build libc++ with support for the global filesystem namespace." ON)
 option(LIBCXX_ENABLE_STDIN "Build libc++ with support for stdin/std::cin." ON)
 option(LIBCXX_ENABLE_STDOUT "Build libc++ with support for stdout/std::cout." ON)
 option(LIBCXX_ENABLE_THREADS "Build libc++ with support for threads." ON)
 option(LIBCXX_ENABLE_THREAD_UNSAFE_C_FUNCTIONS "Build libc++ with support for thread-unsafe C functions" ON)
 option(LIBCXX_ENABLE_MONOTONIC_CLOCK
   "Build libc++ with support for a monotonic clock.
    This option may only be set to OFF when LIBCXX_ENABLE_THREADS=OFF." ON)
+option(LIBCXX_HAS_MUSL_LIBC "Build libc++ with support for the Musl C library" OFF)
 
 # Misc options ----------------------------------------------------------------
 # FIXME: Turn -pedantic back ON. It is currently off because it warns
 # about #include_next which is used everywhere.
 option(LIBCXX_ENABLE_PEDANTIC "Compile with pedantic enabled." OFF)
 option(LIBCXX_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 
 option(LIBCXX_GENERATE_COVERAGE "Enable generating code coverage." OFF)

 endif()
 
 if (LIBCXX_ENABLE_STATIC_ABI_LIBRARY AND LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
     message(FATAL_ERROR "Conflicting options given.
         LIBCXX_ENABLE_STATIC_ABI_LIBRARY cannot be specified with
         LIBCXX_ENABLE_ABI_LINKER_SCRIPT")
 endif()
 
+if (LIBCXX_HAS_MUSL_LIBC AND NOT LIBCXX_INSTALL_SUPPORT_HEADERS)
+  message(FATAL_ERROR "LIBCXX_INSTALL_SUPPORT_HEADERS can not be turned off"
+                      "when building for Musl with LIBCXX_HAS_MUSL_LIBC.")
+endif()
+
 #===============================================================================
 # Configure System
 #===============================================================================
 
 set(LIBCXX_COMPILER    ${CMAKE_CXX_COMPILER})
 set(LIBCXX_SOURCE_DIR  ${CMAKE_CURRENT_SOURCE_DIR})
 set(LIBCXX_BINARY_DIR  ${CMAKE_CURRENT_BINARY_DIR})
 set(LIBCXX_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBCXX_LIBDIR_SUFFIX})

 
 config_define_if_not(LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE)
 config_define_if_not(LIBCXX_ENABLE_STDIN _LIBCPP_HAS_NO_STDIN)
 config_define_if_not(LIBCXX_ENABLE_STDOUT _LIBCPP_HAS_NO_STDOUT)
 config_define_if_not(LIBCXX_ENABLE_THREADS _LIBCPP_HAS_NO_THREADS)
 config_define_if_not(LIBCXX_ENABLE_MONOTONIC_CLOCK _LIBCPP_HAS_NO_MONOTONIC_CLOCK)
 config_define_if_not(LIBCXX_ENABLE_THREAD_UNSAFE_C_FUNCTIONS _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS)
 
+config_define_if(LIBCXX_HAS_MUSL_LIBC _LIBCPP_HAS_MUSL_LIBC)
+
 if (LIBCXX_NEEDS_SITE_CONFIG)
   configure_file(
     include/__config_site.in
     ${LIBCXX_BINARY_DIR}/__config_site
     @ONLY)
   # Provide the config definitions by included the generated __config_site
   # file at compile time.
   add_compile_flags("-include ${LIBCXX_BINARY_DIR}/__config_site")

libcxx/trunk/include/__config

 
 #if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L
 #if defined(__FreeBSD__)
 #define _LIBCPP_HAS_QUICK_EXIT
 #define _LIBCPP_HAS_C11_FEATURES
 #elif defined(__ANDROID__)
 #define _LIBCPP_HAS_QUICK_EXIT
 #elif defined(__linux__)
-#include <features.h>
+#if !defined(_LIBCPP_HAS_MUSL_LIBC)
+# include <features.h>
 #if __GLIBC_PREREQ(2, 15)
 #define _LIBCPP_HAS_QUICK_EXIT
 #endif
 #if __GLIBC_PREREQ(2, 17)
 #define _LIBCPP_HAS_C11_FEATURES
 #endif
+#else // defined(_LIBCPP_HAS_MUSL_LIBC)
+#define _LIBCPP_HAS_QUICK_EXIT
+#define _LIBCPP_HAS_C11_FEATURES
 #endif
+#endif // __linux__
 #endif
 
 #if (__has_feature(cxx_noexcept))
 #  define _NOEXCEPT noexcept
 #  define _NOEXCEPT_(x) noexcept(x)
 #  define _NOEXCEPT_OR_FALSE(x) noexcept(x)
 #else
 #  define _NOEXCEPT throw()

libcxx/trunk/include/__config_site.in

 #cmakedefine _LIBCPP_ABI_VERSION @_LIBCPP_ABI_VERSION@
 #cmakedefine _LIBCPP_ABI_UNSTABLE
 #cmakedefine _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 #cmakedefine _LIBCPP_HAS_NO_STDIN
 #cmakedefine _LIBCPP_HAS_NO_STDOUT
 #cmakedefine _LIBCPP_HAS_NO_THREADS
 #cmakedefine _LIBCPP_HAS_NO_MONOTONIC_CLOCK
 #cmakedefine _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
+#cmakedefine _LIBCPP_HAS_MUSL_LIBC
 
-#endif
+#endif // _LIBCPP_CONFIG_SITE

libcxx/trunk/include/__locale

 #elif defined(__sun__)
 # include <xlocale.h>
 # include <support/solaris/xlocale.h>
 #elif defined(_NEWLIB_VERSION)
 # include <support/newlib/xlocale.h>
 #elif (defined(__GLIBC__) || defined(__APPLE__)      || defined(__FreeBSD__) \
     || defined(__EMSCRIPTEN__) || defined(__IBMCPP__))
 # include <xlocale.h>
+#elif defined(_LIBCPP_HAS_MUSL_LIBC)
+# include <support/musl/xlocale.h>
 #endif // __GLIBC__ || __APPLE__ || __FreeBSD__ || __sun__ || __EMSCRIPTEN__ || __IBMCPP__
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
return _VSTD::use_facet<_VSTD::collate<_CharT> >(*this).compare(
                                        __y.data(), __y.data() + __y.size()) < 0;
 }
 
 // template <class charT> class ctype
 
 class _LIBCPP_TYPE_VIS ctype_base
 {
 public:
-#ifdef __GLIBC__
+#if defined(__GLIBC__)
     typedef unsigned short mask;
     static const mask space  = _ISspace;
     static const mask print  = _ISprint;
     static const mask cntrl  = _IScntrl;
     static const mask upper  = _ISupper;
     static const mask lower  = _ISlower;
     static const mask alpha  = _ISalpha;
     static const mask digit  = _ISdigit;
#elif defined(_WIN32)
     static const mask xdigit = _HEX;
     static const mask blank  = _BLANK;
 # define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_PRINT
 #elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__EMSCRIPTEN__) || defined(__NetBSD__)
 # ifdef __APPLE__
     typedef __uint32_t mask;
 # elif defined(__FreeBSD__)
     typedef unsigned long mask;
-# elif defined(__EMSCRIPTEN__) ||  defined(__NetBSD__)
+# elif defined(__EMSCRIPTEN__) || defined(__NetBSD__) || defined(_LIBCPP_HAS_MUSL_LIBC)
     typedef unsigned short mask;
 # endif
     static const mask space  = _CTYPE_S;
     static const mask print  = _CTYPE_R;
     static const mask cntrl  = _CTYPE_C;
     static const mask upper  = _CTYPE_U;
     static const mask lower  = _CTYPE_L;
     static const mask alpha  = _CTYPE_A;
#elif defined(_NEWLIB_VERSION)
     static const mask digit  = _N;
     static const mask punct  = _P;
     static const mask xdigit = _X | _N;
     static const mask blank  = _B;
 # define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_PRINT
 # define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_ALPHA
 # define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_XDIGIT
 #else
+#if defined(_LIBCPP_HAS_MUSL_LIBC)
+    typedef unsigned short mask;
+#else
     typedef unsigned long mask;
+#endif
     static const mask space  = 1<<0;
     static const mask print  = 1<<1;
     static const mask cntrl  = 1<<2;
     static const mask upper  = 1<<3;
     static const mask lower  = 1<<4;
     static const mask alpha  = 1<<5;
     static const mask digit  = 1<<6;
     static const mask punct  = 1<<7;

 
 #ifdef _CACHED_RUNES
     static const size_t table_size = _CACHED_RUNES;
 #else
     static const size_t table_size = 256;  // FIXME: Don't hardcode this.
 #endif
     _LIBCPP_ALWAYS_INLINE const mask* table() const  _NOEXCEPT {return __tab_;}
     static const mask* classic_table()  _NOEXCEPT;
-#if defined(__GLIBC__) || defined(__EMSCRIPTEN__)
+#if defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(_LIBCPP_HAS_MUSL_LIBC)
     static const int* __classic_upper_table() _NOEXCEPT;
     static const int* __classic_lower_table() _NOEXCEPT;
 #endif
 #if defined(__NetBSD__)
     static const short* __classic_upper_table() _NOEXCEPT;
     static const short* __classic_lower_table() _NOEXCEPT;
 #endif
 

libcxx/trunk/include/support/musl/xlocale.h

+// -*- C++ -*-
+//===------------------- support/musl/xlocale.h ------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// This adds support for the extended locale functions that are currently
+// missing from the Musl C library.
+//
+// This only works when the specified locale is "C" or "POSIX", but that's
+// about as good as we can do without implementing full xlocale support
+// in Musl.
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_SUPPORT_MUSL_XLOCALE_H
+#define _LIBCPP_SUPPORT_MUSL_XLOCALE_H
+
+#include <cstdlib>
+#include <cwchar>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+static inline long long strtoll_l(const char *nptr, char **endptr, int base,
+                                  locale_t) {
+  return strtoll(nptr, endptr, base);
+}
+
+static inline unsigned long long strtoull_l(const char *nptr, char **endptr,
+                                            int base, locale_t) {
+  return strtoull(nptr, endptr, base);
+}
+
+static inline long long wcstoll_l(const wchar_t *nptr, wchar_t **endptr,
+                                  int base, locale_t) {
+  return wcstoll(nptr, endptr, base);
+}
+
+static inline unsigned long long wcstoull_l(const wchar_t *nptr,
+                                            wchar_t **endptr, int base,
+                                            locale_t) {
+  return wcstoull(nptr, endptr, base);
+}
+
+static inline long double wcstold_l(const wchar_t *nptr, wchar_t **endptr,
+                                    locale_t) {
+  return wcstold(nptr, endptr);
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // _LIBCPP_SUPPORT_MUSL_XLOCALE_H

libcxx/trunk/src/locale.cpp

ctype<wchar_t>::do_scan_not(mask m, const char_type* low, const char_type* high) const
     return low;
 }
 
 wchar_t
 ctype<wchar_t>::do_toupper(char_type c) const
 {
 #ifdef _LIBCPP_HAS_DEFAULTRUNELOCALE
     return isascii(c) ? _DefaultRuneLocale.__mapupper[c] : c;
-#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(__NetBSD__)
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || \
+      defined(__NetBSD__) || defined(_LIBCPP_HAS_MUSL_LIBC)
     return isascii(c) ? ctype<char>::__classic_upper_table()[c] : c;
 #else
     return (isascii(c) && iswlower_l(c, _LIBCPP_GET_C_LOCALE)) ? c-L'a'+L'A' : c;
 #endif
 }
 
 const wchar_t*
 ctype<wchar_t>::do_toupper(char_type* low, const char_type* high) const
 {
     for (; low != high; ++low)
 #ifdef _LIBCPP_HAS_DEFAULTRUNELOCALE
         *low = isascii(*low) ? _DefaultRuneLocale.__mapupper[*low] : *low;
-#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(__NetBSD__)
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || \
+      defined(__NetBSD__) || defined(_LIBCPP_HAS_MUSL_LIBC)
         *low = isascii(*low) ? ctype<char>::__classic_upper_table()[*low]
                              : *low;
 #else
         *low = (isascii(*low) && islower_l(*low, _LIBCPP_GET_C_LOCALE)) ? (*low-L'a'+L'A') : *low;
 #endif
     return low;
 }
 
 wchar_t
 ctype<wchar_t>::do_tolower(char_type c) const
 {
 #ifdef _LIBCPP_HAS_DEFAULTRUNELOCALE
     return isascii(c) ? _DefaultRuneLocale.__maplower[c] : c;
-#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(__NetBSD__)
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || \
+      defined(__NetBSD__) || defined(_LIBCPP_HAS_MUSL_LIBC)
     return isascii(c) ? ctype<char>::__classic_lower_table()[c] : c;
 #else
     return (isascii(c) && isupper_l(c, _LIBCPP_GET_C_LOCALE)) ? c-L'A'+'a' : c;
 #endif
 }
 
 const wchar_t*
 ctype<wchar_t>::do_tolower(char_type* low, const char_type* high) const
 {
     for (; low != high; ++low)
 #ifdef _LIBCPP_HAS_DEFAULTRUNELOCALE
         *low = isascii(*low) ? _DefaultRuneLocale.__maplower[*low] : *low;
-#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(__NetBSD__)
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || \
+      defined(__NetBSD__) || defined(_LIBCPP_HAS_MUSL_LIBC)
         *low = isascii(*low) ? ctype<char>::__classic_lower_table()[*low]
                              : *low;
 #else
         *low = (isascii(*low) && isupper_l(*low, _LIBCPP_GET_C_LOCALE)) ? *low-L'A'+L'a' : *low;
 #endif
     return low;
 }
 

 char
 ctype<char>::do_toupper(char_type c) const
 {
 #ifdef _LIBCPP_HAS_DEFAULTRUNELOCALE
     return isascii(c) ?
       static_cast<char>(_DefaultRuneLocale.__mapupper[static_cast<ptrdiff_t>(c)]) : c;
 #elif defined(__NetBSD__)
     return static_cast<char>(__classic_upper_table()[static_cast<unsigned char>(c)]);
-#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__)
-    return isascii(c) ? 
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(_LIBCPP_HAS_MUSL_LIBC)
+    return isascii(c) ?
       static_cast<char>(__classic_upper_table()[static_cast<unsigned char>(c)]) : c;
 #else
     return (isascii(c) && islower_l(c, _LIBCPP_GET_C_LOCALE)) ? c-'a'+'A' : c;
 #endif
 }
 
 const char*
 ctype<char>::do_toupper(char_type* low, const char_type* high) const
 {
     for (; low != high; ++low)
 #ifdef _LIBCPP_HAS_DEFAULTRUNELOCALE
         *low = isascii(*low) ?
           static_cast<char>(_DefaultRuneLocale.__mapupper[static_cast<ptrdiff_t>(*low)]) : *low;
 #elif defined(__NetBSD__)
         *low = static_cast<char>(__classic_upper_table()[static_cast<unsigned char>(*low)]);
-#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__)
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(_LIBCPP_HAS_MUSL_LIBC)
         *low = isascii(*low) ?
           static_cast<char>(__classic_upper_table()[static_cast<size_t>(*low)]) : *low;
 #else
         *low = (isascii(*low) && islower_l(*low, _LIBCPP_GET_C_LOCALE)) ? *low-'a'+'A' : *low;
 #endif
     return low;
 }
 
 char
 ctype<char>::do_tolower(char_type c) const
 {
 #ifdef _LIBCPP_HAS_DEFAULTRUNELOCALE
     return isascii(c) ?
       static_cast<char>(_DefaultRuneLocale.__maplower[static_cast<ptrdiff_t>(c)]) : c;
 #elif defined(__NetBSD__)
     return static_cast<char>(__classic_lower_table()[static_cast<unsigned char>(c)]);
-#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(__NetBSD__)
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(_LIBCPP_HAS_MUSL_LIBC)
     return isascii(c) ?
       static_cast<char>(__classic_lower_table()[static_cast<size_t>(c)]) : c;
 #else
     return (isascii(c) && isupper_l(c, _LIBCPP_GET_C_LOCALE)) ? c-'A'+'a' : c;
 #endif
 }
 
 const char*
 ctype<char>::do_tolower(char_type* low, const char_type* high) const
 {
     for (; low != high; ++low)
 #ifdef _LIBCPP_HAS_DEFAULTRUNELOCALE
         *low = isascii(*low) ? static_cast<char>(_DefaultRuneLocale.__maplower[static_cast<ptrdiff_t>(*low)]) : *low;
 #elif defined(__NetBSD__)
         *low = static_cast<char>(__classic_lower_table()[static_cast<unsigned char>(*low)]);
-#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__)
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(_LIBCPP_HAS_MUSL_LIBC)
         *low = isascii(*low) ? static_cast<char>(__classic_lower_table()[static_cast<size_t>(*low)]) : *low;
 #else
         *low = (isascii(*low) && isupper_l(*low, _LIBCPP_GET_C_LOCALE)) ? *low-'A'+'a' : *low;
 #endif
     return low;
 }
 
 char
ctype<char>::do_narrow(const char_type* low, const char_type* high, char dfault, char* dest) const
     for (; low != high; ++low, ++dest)
         if (isascii(*low))
             *dest = *low;
         else
             *dest = dfault;
     return low;
 }
 
-#ifdef __EMSCRIPTEN__
+#if defined(__EMSCRIPTEN__) || defined(_LIBCPP_HAS_MUSL_LIBC)
 extern "C" const unsigned short ** __ctype_b_loc();
 extern "C" const int ** __ctype_tolower_loc();
 extern "C" const int ** __ctype_toupper_loc();
 #endif
 
 #ifdef _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE
 const ctype<char>::mask*
 ctype<char>::classic_table()  _NOEXCEPT

 #elif defined(__GLIBC__)
     return _LIBCPP_GET_C_LOCALE->__ctype_b;
 #elif __sun__
     return __ctype_mask;
 #elif defined(_LIBCPP_MSVCRT) || defined(__MINGW32__)
     return _ctype+1; // internal ctype mask table defined in msvcrt.dll
 // This is assumed to be safe, which is a nonsense assumption because we're
 // going to end up dereferencing it later...
-#elif defined(__EMSCRIPTEN__)
+#elif defined(__EMSCRIPTEN__) || defined(_LIBCPP_HAS_MUSL_LIBC)
     return *__ctype_b_loc();
 #elif defined(_NEWLIB_VERSION)
     // Newlib has a 257-entry table in ctype_.c, where (char)0 starts at [1].
     return _ctype_ + 1;
 #elif defined(_AIX)
     return (const unsigned int *)__lc_ctype_ptr->obj->mask;
 #else
     // Platform not supported: abort so the person doing the port knows what to

 }
 
 const short*
 ctype<char>::__classic_upper_table() _NOEXCEPT
 {
     return _C_toupper_tab_ + 1;
 }
 
-#elif defined(__EMSCRIPTEN__)
+#elif defined(__EMSCRIPTEN__) || defined(_LIBCPP_HAS_MUSL_LIBC)
 const int*
 ctype<char>::__classic_lower_table() _NOEXCEPT
 {
     return *__ctype_tolower_loc();
 }
 
 const int*
 ctype<char>::__classic_upper_table() _NOEXCEPT
 {
     return *__ctype_toupper_loc();
 }
-#endif // __GLIBC__ || __EMSCRIPTEN__ || __NETBSD__
+#endif // __GLIBC__ || __NETBSD__ || __EMSCRIPTEN__ || defined(_LIBCPP_HAS_MUSL_LIBC)
 
 // template <> class ctype_byname<char>
 
 ctype_byname<char>::ctype_byname(const char* name, size_t refs)
     : ctype<char>(0, false, refs),
       __l(newlocale(LC_ALL_MASK, name, 0))
 {
 #ifndef _LIBCPP_NO_EXCEPTIONS