[SystemZ][z/OS] ASCII/EBCDIC support with no coexistence

[muiez]

Summary

The aim of this patch is to break up the larger patch (https://reviews.llvm.org/D111323) to be more upstream friendly. In particular, this patch adds the char encoding sensitive changes but does not use inline namespaces as before. The use of namespaces to build both versions of the library, and localization of error messages will follow in a subsequent patch.

[muiez]

Remove LIBCXXABI_BUILD_ZOS_ENCODING

[muiez]

Ping

[muiez]

Remove LIBCXX_BUILD_ZOS_ENCODING

[zibi]

LGTM

[zibi]

We need to pass "-fzos-le-char-mode=ebcdic for libcxx same as we do for libcxxabi

libcxx/CMakeLists.txt

477

add_target_flags_if_supported("-fzos-le-char-mode=ebcdic")

[muiez]

Add default encoding

[muiez]

ping @libc++ @libc++ab

[zibi]

LGTM

[ldionne]

A couple of minor comments -- I don't see anything wrong specifically with this patch, but I'm eager to see the follow-up patches.

libcxx/include/regex

1314–1322

Those should be inline functions instead of macros.

libcxxabi/CMakeLists.txt

272

What does this flag do? Isn't it necessary only when building using EBCDIC?

[muiez]

Using inline functions instead of macros

[muiez]

libcxxabi/CMakeLists.txt

272

This flag ensures that our default encoding is ebcdic. In a subsequent patch, we build the ascii version as a separate library and override this flag.

[ldionne]

libcxx/include/regex

1314

If you look at the surrounding code, we uglify everything with double underscores. The reason is that names starting with double underscores are reserved for the implementation, so users wouldn't be allowed to define a macro like is_07 that would (in the status quo) break our implementation. You'll need to do that here.

libcxxabi/CMakeLists.txt

272

I think this should be enclosed in if (MVS) or whatever the CMake check is, then. Otherwise, if another compiler supports that flag (I assume Clang will support that flag at some point?), we'd start using it everywhere.

[muiez]

safeguard to z/OS, use double underscore function names

[muiez]

Great points! Updated to account for this.

[ldionne]

LGTM with my __to_lower suggestion.

libcxx/include/regex

1357

Can we change this into:

__ch = __to_lower(__ch_);

Sorry I didn't spot it before. As it stands, it really looks like a bug until you realize __ch is passed by reference.

[muiez]

addressed comment to be more readable

libcxx/CMakeLists.txt

 
 # Include macros for adding and removing libc++ flags.
 include(HandleLibcxxFlags)
 
 # Target flags ================================================================
 # These flags get added to CMAKE_CXX_FLAGS and CMAKE_C_FLAGS so that
 # 'config-ix' use them during feature checks. It also adds them to both
 # 'LIBCXX_COMPILE_FLAGS' and 'LIBCXX_LINK_FLAGS'
+add_target_flags_if_supported("-fzos-le-char-mode=ebcdic")
+
 if(LIBCXX_TARGET_TRIPLE)
   add_target_flags_if_supported("--target=${LIBCXX_TARGET_TRIPLE}")
 endif()
 if(LIBCXX_SYSROOT)
   add_target_flags_if_supported("--sysroot=${LIBCXX_SYSROOT}")
 endif()
 if(LIBCXX_GCC_TOOLCHAIN)
   add_target_flags_if_supported("--gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")

libcxx/include/__config

 #  include <features.h>
 #  if defined(__GLIBC_PREREQ)
 #    define _LIBCPP_GLIBC_PREREQ(a, b) __GLIBC_PREREQ(a, b)
 #  else
 #    define _LIBCPP_GLIBC_PREREQ(a, b) 0
 #  endif // defined(__GLIBC_PREREQ)
 #endif // defined(__linux__)
 
+#if defined(__MVS__)
+#  include <features.h> // for __NATIVE_ASCII_F
+#endif
+
 #ifdef __LITTLE_ENDIAN__
 #  if __LITTLE_ENDIAN__
 #    define _LIBCPP_LITTLE_ENDIAN
 #  endif  // __LITTLE_ENDIAN__
 #endif // __LITTLE_ENDIAN__
 
 #ifdef __BIG_ENDIAN__
 #  if __BIG_ENDIAN__

 // Some systems do not provide gets() in their C library, for security reasons.
 #if defined(_LIBCPP_MSVCRT) || \
     (defined(__FreeBSD_version) && __FreeBSD_version >= 1300043) || \
     defined(__OpenBSD__)
 #   define _LIBCPP_C_HAS_NO_GETS
 #endif
 
 #if defined(__BIONIC__) || defined(__NuttX__) ||      \
-    defined(__Fuchsia__) || defined(__wasi__) || defined(_LIBCPP_HAS_MUSL_LIBC) || \
-    defined(__MVS__) || defined(__OpenBSD__)
+    defined(__Fuchsia__) || defined(__wasi__) ||      \
+    defined(_LIBCPP_HAS_MUSL_LIBC) || defined(__OpenBSD__)
 #define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE
 #endif
 
 #if __has_feature(cxx_atomic) || __has_extension(c_atomic) || __has_keyword(_Atomic)
 #  define _LIBCPP_HAS_C_ATOMIC_IMP
 #elif defined(_LIBCPP_COMPILER_GCC)
 #  define _LIBCPP_HAS_GCC_ATOMIC_IMP
 #endif

libcxx/include/__locale

#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;
     static const mask __regex_word = 0x80;
 # define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_PRINT
 # define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_ALPHA
 # define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_XDIGIT
+#elif defined(__MVS__)
+    static const mask __regex_word = 0x8000;
+# if defined(__NATIVE_ASCII_F)`
+    typedef unsigned int mask;
+    static const mask space  = _ISSPACE_A;
+    static const mask print  = _ISPRINT_A;
+    static const mask cntrl  = _ISCNTRL_A;
+    static const mask upper  = _ISUPPER_A;
+    static const mask lower  = _ISLOWER_A;
+    static const mask alpha  = _ISALPHA_A;
+    static const mask digit  = _ISDIGIT_A;
+    static const mask punct  = _ISPUNCT_A;
+    static const mask xdigit = _ISXDIGIT_A;
+    static const mask blank  = _ISBLANK_A;
+# else
+    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;
+    static const mask punct  = __ISPUNCT;
+    static const mask xdigit = __ISXDIGIT;
+    static const mask blank  = __ISBLANK;
+# endif
 #else
 # error unknown rune table for this platform -- do you mean to define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE?
 #endif
     static const mask alnum  = alpha | digit;
     static const mask graph  = alnum | punct;
 
     _LIBCPP_INLINE_VISIBILITY ctype_base() {}
 };

 #if defined(__GLIBC__) || defined(__EMSCRIPTEN__)
     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
+#if defined(__MVS__)
+    static const unsigned short* __classic_upper_table() _NOEXCEPT;
+    static const unsigned short* __classic_lower_table() _NOEXCEPT;
+#endif
 
 protected:
     ~ctype();
     virtual char_type do_toupper(char_type __c) const;
     virtual const char_type* do_toupper(char_type* __low, const char_type* __high) const;
     virtual char_type do_tolower(char_type __c) const;
     virtual const char_type* do_tolower(char_type* __low, const char_type* __high) const;
     virtual char_type do_widen(char __c) const;

libcxx/include/regex

 bool
 regex_traits<_CharT>::isctype(char_type __c, char_class_type __m) const
 {
     if (__ct_->is(__m, __c))
         return true;
     return (__c == '_' && (__m & __regex_word));
 }
 
+inline _LIBCPP_INLINE_VISIBILITY
+bool is_07(unsigned char c)
+{
+    return (c & 0xF8u) ==
+#if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
+        0xF0;
+#else
+        0x30;
+#endif
+}
+
+inline _LIBCPP_INLINE_VISIBILITY
+bool is_89(unsigned char c)
+{
+    return (c & 0xFEu) ==
+#if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
+        0xF8;
+#else
+        0x38;
+#endif
+}
+
+inline _LIBCPP_INLINE_VISIBILITY
+void to_lower(unsigned char& c)
+{
+#if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
+    c &= 0xBF;
+#else
+    c |= 0x20;
+#endif
+}
+
 template <class _CharT>
 int
 regex_traits<_CharT>::__regex_traits_value(unsigned char __ch, int __radix)
 {
-    if ((__ch & 0xF8u) == 0x30)  // '0' <= __ch && __ch <= '7'
+    if (is_07(__ch))  // '0' <= __ch && __ch <= '7'
         return __ch - '0';
     if (__radix != 8)
     {
-        if ((__ch & 0xFEu) == 0x38)  // '8' <= __ch && __ch <= '9'
+        if (is_89(__ch))  // '8' <= __ch && __ch <= '9'
             return __ch - '0';
         if (__radix == 16)
         {
-            __ch |= 0x20;  // tolower
+            to_lower(__ch);  // tolower
             if ('a' <= __ch && __ch <= 'f')
                 return __ch - ('a' - 10);
         }
     }
     return -1;
 }
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS

libcxx/src/locale.cpp

 }
 
 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__)
+      defined(__NetBSD__) || defined(__MVS__)
     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__)
+      defined(__NetBSD__) || defined(__MVS__)
         *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__)
+      defined(__NetBSD__) || defined(__MVS__)
     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__)
+      defined(__NetBSD__) || defined(__MVS__)
         *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__)
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(__MVS__)
     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(__MVS__)
         *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__)
+#elif defined(__GLIBC__) || defined(__EMSCRIPTEN__) || defined(__MVS__)
     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(__MVS__)
         *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
#elif defined(_LIBCPP_MSVCRT) || defined(__MINGW32__)
     return __pctype_func();
 #elif defined(__EMSCRIPTEN__)
     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;
+#elif defined(__MVS__)
+# if defined(__NATIVE_ASCII_F)
+    return const_cast<const ctype<char>::mask*> (__OBJ_DATA(__lc_ctype_a)->mask);
+# else
+    return const_cast<const ctype<char>::mask*> (__ctypec);
+# endif
 #else
     // Platform not supported: abort so the person doing the port knows what to
     // fix
 # warning  ctype<char>::classic_table() is not implemented
     printf("ctype<char>::classic_table() is not implemented\n");
     abort();
     return NULL;
 #endif
ctype<char>::__classic_lower_table() noexcept
     return *__ctype_tolower_loc();
 }
 
 const int*
 ctype<char>::__classic_upper_table() noexcept
 {
     return *__ctype_toupper_loc();
 }
-#endif // __GLIBC__ || __NETBSD__ || __EMSCRIPTEN__
+#elif defined(__MVS__)
+const unsigned short*
+ctype<char>::__classic_lower_table() _NOEXCEPT
+{
+# if defined(__NATIVE_ASCII_F)
+  return const_cast<const unsigned short*>(__OBJ_DATA(__lc_ctype_a)->lower);
+# else
+  return const_cast<const unsigned short*>(__ctype + __TOLOWER_INDEX);
+# endif
+}
+const unsigned short *
+ctype<char>::__classic_upper_table() _NOEXCEPT
+{
+# if defined(__NATIVE_ASCII_F)
+  return const_cast<const unsigned short*>(__OBJ_DATA(__lc_ctype_a)->upper);
+# else
+  return const_cast<const unsigned short*>(__ctype + __TOUPPER_INDEX);
+# endif
+}
+#endif // __GLIBC__ || __NETBSD__ || __EMSCRIPTEN__ || __MVS__
 
 // 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))
 {
     if (__l == 0)

libcxx/src/regex.cpp

 namespace {
 
 struct collationnames
 {
     const char* elem_;
     char char_;
 };
 
+#if defined(__MVS__) && !defined(__NATIVE_ASCII_F)
+// EBCDIC IBM-1047
+// Sorted via the EBCDIC collating sequence
+const collationnames collatenames[] =
+{
+    {"a", 0x81},
+    {"alert", 0x2f},
+    {"ampersand", 0x50},
+    {"apostrophe", 0x7d},
+    {"asterisk", 0x5c},
+    {"b", 0x82},
+    {"backslash", 0xe0},
+    {"backspace", 0x16},
+    {"c", 0x83},
+    {"carriage-return", 0xd},
+    {"circumflex", 0x5f},
+    {"circumflex-accent", 0x5f},
+    {"colon", 0x7a},
+    {"comma", 0x6b},
+    {"commercial-at", 0x7c},
+    {"d", 0x84},
+    {"dollar-sign", 0x5b},
+    {"e", 0x85},
+    {"eight", 0xf8},
+    {"equals-sign", 0x7e},
+    {"exclamation-mark", 0x5a},
+    {"f", 0x86},
+    {"five", 0xf5},
+    {"form-feed", 0xc},
+    {"four", 0xf4},
+    {"full-stop", 0x4b},
+    {"g", 0x87},
+    {"grave-accent", 0x79},
+    {"greater-than-sign", 0x6e},
+    {"h", 0x88},
+    {"hyphen", 0x60},
+    {"hyphen-minus", 0x60},
+    {"i", 0x89},
+    {"j", 0x91},
+    {"k", 0x92},
+    {"l", 0x93},
+    {"left-brace", 0xc0},
+    {"left-curly-bracket", 0xc0},
+    {"left-parenthesis", 0x4d},
+    {"left-square-bracket", 0xad},
+    {"less-than-sign", 0x4c},
+    {"low-line", 0x6d},
+    {"m", 0x94},
+    {"n", 0x95},
+    {"newline", 0x15},
+    {"nine", 0xf9},
+    {"number-sign", 0x7b},
+    {"o", 0x96},
+    {"one", 0xf1},
+    {"p", 0x97},
+    {"percent-sign", 0x6c},
+    {"period", 0x4b},
+    {"plus-sign", 0x4e},
+    {"q", 0x98},
+    {"question-mark", 0x6f},
+    {"quotation-mark", 0x7f},
+    {"r", 0x99},
+    {"reverse-solidus", 0xe0},
+    {"right-brace", 0xd0},
+    {"right-curly-bracket", 0xd0},
+    {"right-parenthesis", 0x5d},
+    {"right-square-bracket", 0xbd},
+    {"s", 0xa2},
+    {"semicolon", 0x5e},
+    {"seven", 0xf7},
+    {"six", 0xf6},
+    {"slash", 0x61},
+    {"solidus", 0x61},
+    {"space", 0x40},
+    {"t", 0xa3},
+    {"tab", 0x5},
+    {"three", 0xf3},
+    {"tilde", 0xa1},
+    {"two", 0xf2},
+    {"u", 0xa4},
+    {"underscore", 0x6d},
+    {"v", 0xa5},
+    {"vertical-line", 0x4f},
+    {"vertical-tab", 0xb},
+    {"w", 0xa6},
+    {"x", 0xa7},
+    {"y", 0xa8},
+    {"z", 0xa9},
+    {"zero", 0xf0},
+    {"A", 0xc1},
+    {"B", 0xc2},
+    {"C", 0xc3},
+    {"D", 0xc4},
+    {"E", 0xc5},
+    {"F", 0xc6},
+    {"G", 0xc7},
+    {"H", 0xc8},
+    {"I", 0xc9},
+    {"J", 0xd1},
+    {"K", 0xd2},
+    {"L", 0xd3},
+    {"M", 0xd4},
+    {"N", 0xd5},
+    {"NUL", 0},
+    {"O", 0xd6},
+    {"P", 0xd7},
+    {"Q", 0xd8},
+    {"R", 0xd9},
+    {"S", 0xe2},
+    {"T", 0xe3},
+    {"U", 0xe4},
+    {"V", 0xe5},
+    {"W", 0xe6},
+    {"X", 0xe7},
+    {"Y", 0xe8},
+    {"Z", 0xe9}
+};
+#else
+// ASCII
 const collationnames collatenames[] =
 {
     {"A", 0x41},
     {"B", 0x42},
     {"C", 0x43},
     {"D", 0x44},
     {"E", 0x45},
     {"F", 0x46},
const collationnames collatenames[] =
     {"vertical-line", 0x7c},
     {"vertical-tab", 0x0b},
     {"w", 0x77},
     {"x", 0x78},
     {"y", 0x79},
     {"z", 0x7a},
     {"zero", 0x30}
 };
+#endif
 
 struct classnames
 {
     const char* elem_;
     regex_traits<char>::char_class_type mask_;
 };
 
 const classnames ClassNames[] =

libcxxabi/CMakeLists.txt

 # Include macros for adding and removing libc++abi flags.
 include(HandleLibcxxabiFlags)
 
 #===============================================================================
 # Setup Compiler Flags
 #===============================================================================
 
 # Configure target flags
+add_target_flags_if_supported("-fzos-le-char-mode=ebcdic")
+
 if(LIBCXXABI_TARGET_TRIPLE)
   add_target_flags_if_supported("--target=${LIBCXXABI_TARGET_TRIPLE}")
 endif()
 if(LIBCXXABI_GCC_TOOLCHAIN)
   add_target_flags_if_supported("--gcc-toolchain=${LIBCXXABI_GCC_TOOLCHAIN}")
 endif()
 if(LIBCXXABI_SYSROOT)
   add_target_flags_if_supported("--sysroot=${LIBCXXABI_SYSROOT}")