[Bug libstdc++/106477] With -fno-exception operator new(nothrow) aborts instead of returning null

["redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106477

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
A partial solution, but needs better preprocessor checks around it:

diff --git a/libstdc++-v3/libsupc++/new_op.cc
b/libstdc++-v3/libsupc++/new_op.cc
index 3a6540a3cd9..b1f31bac7e8 100644
--- a/libstdc++-v3/libsupc++/new_op.cc
+++ b/libstdc++-v3/libsupc++/new_op.cc
@@ -57,3 +57,16 @@ operator new (std::size_t sz) _GLIBCXX_THROW
(std::bad_alloc)

   return p;
 }
+
+#if _GLIBCXX_SHARED && __pic__ && defined _GLIBCXX_MANGLE_SIZE_T \
+  && __has_cpp_attribute(gnu::alias) && __has_cpp_attribute(gnu::visibility)
+namespace __gnu_cxx
+{
+#define STR_(A) #A
+#define STR(A) STR_(A)
+#define OP_NEW "_Znw" STR(_GLIBCXX_MANGLE_SIZE_T)
+
+  [[gnu::alias(OP_NEW), gnu::visibility("hidden")]]
+  void * __default_op_new (std::size_t sz) _GLIBCXX_THROW (std::bad_alloc);
+}
+#endif
diff --git a/libstdc++-v3/libsupc++/new_opnt.cc
b/libstdc++-v3/libsupc++/new_opnt.cc
index 3822e04c8cf..23e9981a958 100644
--- a/libstdc++-v3/libsupc++/new_opnt.cc
+++ b/libstdc++-v3/libsupc++/new_opnt.cc
@@ -26,11 +26,43 @@
 #include <bits/exception_defines.h>
 #include "new"

+
+#if _GLIBCXX_SHARED && __pic__
 extern "C" void *malloc (std::size_t);
+namespace __gnu_cxx { void * __default_op_new (std::size_t sz); }
+#endif

 _GLIBCXX_WEAK_DEFINITION void *
 operator new (std::size_t sz, const std::nothrow_t&) noexcept
 {
+  // TODO: Only do this for libstdc++.so not libstdc++.a
+  // TODO: Need proper checks that alias + visibility works correctly.
+#if _GLIBCXX_SHARED && __pic__ && defined _GLIBCXX_MANGLE_SIZE_T \
+  && __has_cpp_attribute(gnu::alias) && __has_cpp_attribute(gnu::visibility)
+  void* (*op_new)(std::size_t) = &::operator new;
+  if (op_new == __gnu_cxx::__default_op_new)
+    {
+      // We know that operator new(size_t) has not been replaced,
+      // and we know that the default version just uses malloc.
+      // So we can implement this directly, without the overhead
+      // of handling bad_alloc exceptions.
+
+      /* malloc (0) is unpredictable; avoid it.  */
+      if (__builtin_expect (sz == 0, false))
+       sz = 1;
+
+      void *p;
+      while ((p = malloc (sz)) == 0)
+       {
+         std::new_handler handler = std::get_new_handler ();
+         if (! handler)
+           return nullptr;
+         handler ();
+       }
+      return p;
+    }
+#endif
+
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // 206. operator new(size_t, nothrow) may become unlinked to ordinary
   // operator new if ordinary version replaced