Index: libcxx/benchmarks/CMakeLists.txt
===================================================================
--- libcxx/benchmarks/CMakeLists.txt
+++ libcxx/benchmarks/CMakeLists.txt
@@ -192,6 +192,7 @@
     std_format_spec_string_unicode.bench.cpp
     string.bench.cpp
     stringstream.bench.cpp
+    system_error.bench.cpp
     to_chars.bench.cpp
     unordered_set_operations.bench.cpp
     util_smartptr.bench.cpp
Index: libcxx/benchmarks/system_error.bench.cpp
===================================================================
--- /dev/null
+++ libcxx/benchmarks/system_error.bench.cpp
@@ -0,0 +1,30 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <string>
+#include <system_error>
+
+#include "benchmark/benchmark.h"
+
+static void BM_SystemErrorWithMessage(benchmark::State& state) {
+  for (auto _ : state) {
+    std::error_code ec{};
+    benchmark::DoNotOptimize(std::system_error{ec, ""});
+  }
+}
+BENCHMARK(BM_SystemErrorWithMessage);
+
+static void BM_SystemErrorWithoutMessage(benchmark::State& state) {
+  for (auto _ : state) {
+    std::error_code ec{};
+    benchmark::DoNotOptimize(std::system_error{ec});
+  }
+}
+BENCHMARK(BM_SystemErrorWithoutMessage);
+
+BENCHMARK_MAIN();
Index: libcxx/docs/ReleaseNotes/18.rst
===================================================================
--- libcxx/docs/ReleaseNotes/18.rst
+++ libcxx/docs/ReleaseNotes/18.rst
@@ -74,6 +74,8 @@
 ABI Affecting Changes
 ---------------------
 
+- The symbol of a non-visible function part of ``std::system_error`` was removed.
+  This is not a breaking change as the private function ``__init`` was never referenced internally outside of the dylib
 
 Build System Changes
 --------------------
Index: libcxx/include/__system_error/system_error.h
===================================================================
--- libcxx/include/__system_error/system_error.h
+++ libcxx/include/__system_error/system_error.h
@@ -36,9 +36,6 @@
   ~system_error() _NOEXCEPT override;
 
   _LIBCPP_HIDE_FROM_ABI const error_code& code() const _NOEXCEPT { return __ec_; }
-
-private:
-  static string __init(const error_code&, string);
 };
 
 _LIBCPP_NORETURN _LIBCPP_EXPORTED_FROM_ABI void __throw_system_error(int __ev, const char* __what_arg);
Index: libcxx/lib/abi/CHANGELOG.TXT
===================================================================
--- libcxx/lib/abi/CHANGELOG.TXT
+++ libcxx/lib/abi/CHANGELOG.TXT
@@ -12,6 +12,25 @@
 
 New entries should be added directly below the "Version" header.
 
+------------
+Version 18.0
+------------
+
+* [libc++] Remove symbol for std::system_error from the dylib
+
+  This patch removes a symbol defined in the library for std::system_error.
+  The symbol '__init' was defined as a private static function as part of the
+  system_error class and was never visible. The addition of this symbol to the ABI was most likely accidental.
+  The function '__init' is replaced by another equivalent function which is placed in the
+  anonymous namespace of the std::system_error source code file.
+  There are no internal references to this symbol which seems to support the reasoning that
+  this was never used outside of the dylib.
+  The deletion of the symbol should not be a breaking change.
+
+All platforms
+  -------------
+  Symbol removed: _ZNSt3__112system_error6__initERKNS_10error_codeENS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE
+
 ------------
 Version 17.0
 ------------
Index: libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
===================================================================
--- libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1062,7 +1062,6 @@
 {'is_defined': True, 'name': '__ZNSt3__112strstreambufD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112strstreambufD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112strstreambufD2Ev', 'type': 'FUNC'}
-{'is_defined': True, 'name': '__ZNSt3__112system_error6__initERKNS_10error_codeENS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112system_errorC1ENS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112system_errorC1ENS_10error_codeEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112system_errorC1ENS_10error_codeERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
Index: libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
===================================================================
--- libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -393,7 +393,6 @@
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112strstreambufD0Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112strstreambufD1Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112strstreambufD2Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
-{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112system_error6__initERKNS_10error_codeENS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeEPKc', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
Index: libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
===================================================================
--- libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -393,7 +393,6 @@
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112strstreambufD0Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112strstreambufD1Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112strstreambufD2Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
-{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112system_error6__initERKNS_10error_codeENS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeEPKc', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
Index: libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
===================================================================
--- libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1062,7 +1062,6 @@
 {'is_defined': True, 'name': '__ZNSt3__112strstreambufD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112strstreambufD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112strstreambufD2Ev', 'type': 'FUNC'}
-{'is_defined': True, 'name': '__ZNSt3__112system_error6__initERKNS_10error_codeENS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112system_errorC1ENS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112system_errorC1ENS_10error_codeEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__112system_errorC1ENS_10error_codeERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
Index: libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
===================================================================
--- libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -757,7 +757,6 @@
 {'is_defined': True, 'name': '_ZNSt3__112strstreambufD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112strstreambufD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112strstreambufD2Ev', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__112system_error6__initERKNS_10error_codeENS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
Index: libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
===================================================================
--- libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -755,7 +755,6 @@
 {'is_defined': True, 'name': '_ZNSt3__112strstreambufD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112strstreambufD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112strstreambufD2Ev', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__112system_error6__initERKNS_10error_codeENS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
Index: libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
===================================================================
--- libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
+++ libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
@@ -727,7 +727,6 @@
 {'is_defined': True, 'name': '_ZNSt3__112strstreambufD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112strstreambufD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112strstreambufD2Ev', 'type': 'FUNC'}
-{'is_defined': True, 'name': '_ZNSt3__112system_error6__initERKNS_10error_codeENS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeEPKc', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112system_errorC1ENS_10error_codeERKNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE', 'type': 'FUNC'}
Index: libcxx/src/system_error.cpp
===================================================================
--- libcxx/src/system_error.cpp
+++ libcxx/src/system_error.cpp
@@ -59,8 +59,8 @@
     return *this == code.category() && code.value() == condition;
 }
 
-#if !defined(_LIBCPP_HAS_NO_THREADS)
 namespace {
+#if !defined(_LIBCPP_HAS_NO_THREADS)
 
 //  GLIBC also uses 1024 as the maximum buffer size internally.
 constexpr size_t strerror_buff_size = 1024;
@@ -128,8 +128,26 @@
     return string(error_message);
 }
 #endif
+
+#endif // !defined(_LIBCPP_HAS_NO_THREADS)
+
+string make_error_str(const error_code& ec, string what_arg) {
+    if (ec) {
+        if (!what_arg.empty()) {
+            what_arg += ": ";
+        }
+        what_arg += ec.message();
+    }
+    return what_arg;
+}
+
+string make_error_str(const error_code& ec) {
+    if (ec) {
+        return ec.message();
+    }
+    return string();
+}
 } // end namespace
-#endif
 
 string
 __do_message::message(int ev) const
@@ -232,50 +250,38 @@
 
 // system_error
 
-string
-system_error::__init(const error_code& ec, string what_arg)
-{
-    if (ec)
-    {
-        if (!what_arg.empty())
-            what_arg += ": ";
-        what_arg += ec.message();
-    }
-    return what_arg;
-}
-
 system_error::system_error(error_code ec, const string& what_arg)
-    : runtime_error(__init(ec, what_arg)),
+    : runtime_error(make_error_str(ec, what_arg)),
       __ec_(ec)
 {
 }
 
 system_error::system_error(error_code ec, const char* what_arg)
-    : runtime_error(__init(ec, what_arg)),
+    : runtime_error(make_error_str(ec, what_arg)),
       __ec_(ec)
 {
 }
 
 system_error::system_error(error_code ec)
-    : runtime_error(__init(ec, "")),
+    : runtime_error(make_error_str(ec)),
       __ec_(ec)
 {
 }
 
 system_error::system_error(int ev, const error_category& ecat, const string& what_arg)
-    : runtime_error(__init(error_code(ev, ecat), what_arg)),
+    : runtime_error(make_error_str(error_code(ev, ecat), what_arg)),
       __ec_(error_code(ev, ecat))
 {
 }
 
 system_error::system_error(int ev, const error_category& ecat, const char* what_arg)
-    : runtime_error(__init(error_code(ev, ecat), what_arg)),
+    : runtime_error(make_error_str(error_code(ev, ecat), what_arg)),
       __ec_(error_code(ev, ecat))
 {
 }
 
 system_error::system_error(int ev, const error_category& ecat)
-    : runtime_error(__init(error_code(ev, ecat), "")),
+    : runtime_error(make_error_str(error_code(ev, ecat))),
       __ec_(error_code(ev, ecat))
 {
 }