--- gcc/cp/mangle.cc.jj	2024-01-12 10:07:31.248231747 +0100
+++ gcc/cp/mangle.cc	2024-01-12 11:37:35.790915463 +0100
@@ -1247,6 +1247,8 @@ write_nested_name (const tree decl)
 	    write_char ('R');
 	}
     }
+  else if (DECL_XOBJ_MEMBER_FUNCTION_P (decl))
+    write_char ('H');
 
   /* Is this a template instance?  */
   if (tree info = maybe_template_info (decl))
--- gcc/testsuite/g++.dg/abi/mangle79.C.jj	2024-01-12 13:18:20.782917924 +0100
+++ gcc/testsuite/g++.dg/abi/mangle79.C	2024-01-12 13:26:01.297433970 +0100
@@ -0,0 +1,61 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+struct S {
+  static void foo (S);
+  void foo (this S);		// { dg-warning "explicit object member function only available with" "" { target c++20_down } }
+  template <int N, typename T>
+  static void bar (S, T);
+  template <int N, typename T>
+  void bar (this S, T);		// { dg-warning "explicit object member function only available with" "" { target c++20_down } }
+  static void baz (const S &);
+  void baz (this const S &);	// { dg-warning "explicit object member function only available with" "" { target c++20_down } }
+};
+
+void
+S::foo (S)
+{
+}
+
+void
+S::foo (this S)			// { dg-warning "explicit object member function only available with" "" { target c++20_down } }
+{
+}
+
+template <int N, typename T>
+void
+S::bar (S, T)
+{
+}
+
+template <int N, typename T>
+void
+S::bar (this S, T)		// { dg-warning "explicit object member function only available with" "" { target c++20_down } }
+{
+}
+
+void
+S::baz (const S &)
+{
+}
+
+void
+S::baz (this const S &)		// { dg-warning "explicit object member function only available with" "" { target c++20_down } }
+{
+}
+
+void
+qux (S *p)
+{
+  S::foo (*p);
+  p->foo ();
+  S::bar <5> (*p, 0);
+  p->bar <5> (0);
+}
+
+// { dg-final { scan-assembler "_ZN1S3fooES_" } }
+// { dg-final { scan-assembler "_ZNH1S3fooES_" } }
+// { dg-final { scan-assembler "_ZN1S3barILi5EiEEvS_T0_" } }
+// { dg-final { scan-assembler "_ZNH1S3barILi5EiEEvS_T0_" } }
+// { dg-final { scan-assembler "_ZN1S3bazERKS_" } }
+// { dg-final { scan-assembler "_ZNH1S3bazERKS_" } }
--- include/demangle.h.jj	2024-01-03 12:07:25.330409694 +0100
+++ include/demangle.h	2024-01-12 11:43:27.543915280 +0100
@@ -314,6 +314,8 @@ enum demangle_component_type
   /* C++11: An rvalue reference modifying a member function.  The one
      subtree is the type which is being referenced.  */
   DEMANGLE_COMPONENT_RVALUE_REFERENCE_THIS,
+  /* C++23: A member function with explict object parameter.  */
+  DEMANGLE_COMPONENT_XOBJ_MEMBER_FUNCTION,
   /* A vendor qualifier.  The left subtree is the type which is being
      qualified, and the right subtree is the name of the
      qualifier.  */
--- libiberty/cp-demangle.c.jj	2024-01-03 12:07:48.498085118 +0100
+++ libiberty/cp-demangle.c	2024-01-12 13:06:04.526281733 +0100
@@ -581,6 +581,7 @@ static char *d_demangle (const char *, i
     case DEMANGLE_COMPONENT_CONST_THIS:			\
     case DEMANGLE_COMPONENT_REFERENCE_THIS:		\
     case DEMANGLE_COMPONENT_RVALUE_REFERENCE_THIS:	\
+    case DEMANGLE_COMPONENT_XOBJ_MEMBER_FUNCTION:	\
     case DEMANGLE_COMPONENT_TRANSACTION_SAFE:		\
     case DEMANGLE_COMPONENT_NOEXCEPT:			\
     case DEMANGLE_COMPONENT_THROW_SPEC
@@ -749,6 +750,9 @@ d_dump (struct demangle_component *dc, i
     case DEMANGLE_COMPONENT_RVALUE_REFERENCE_THIS:
       printf ("rvalue reference this\n");
       break;
+    case DEMANGLE_COMPONENT_XOBJ_MEMBER_FUNCTION:
+      printf ("explicit object parameter\n");
+      break;
     case DEMANGLE_COMPONENT_TRANSACTION_SAFE:
       printf ("transaction_safe this\n");
       break;
@@ -1547,6 +1551,8 @@ d_name (struct d_info *di, int substable
 
 /* <nested-name> ::= N [<CV-qualifiers>] [<ref-qualifier>] <prefix> <unqualified-name> E
                  ::= N [<CV-qualifiers>] [<ref-qualifier>] <template-prefix> <template-args> E
+                 ::= N H <prefix> <unqualified-name> E
+                 ::= N H <template-prefix> <template-args> E
 */
 
 static struct demangle_component *
@@ -1559,13 +1565,24 @@ d_nested_name (struct d_info *di)
   if (! d_check_char (di, 'N'))
     return NULL;
 
-  pret = d_cv_qualifiers (di, &ret, 1);
-  if (pret == NULL)
-    return NULL;
+  if (d_peek_char (di) == 'H')
+    {
+      d_advance (di, 1);
+      di->expansion += sizeof "this";
+      pret = &ret;
+      rqual = d_make_comp (di, DEMANGLE_COMPONENT_XOBJ_MEMBER_FUNCTION,
+			   NULL, NULL);
+    }
+  else
+    {
+      pret = d_cv_qualifiers (di, &ret, 1);
+      if (pret == NULL)
+	return NULL;
 
-  /* Parse the ref-qualifier now and then attach it
-     once we have something to attach it to.  */
-  rqual = d_ref_qualifier (di, NULL);
+      /* Parse the ref-qualifier now and then attach it
+	 once we have something to attach it to.  */
+      rqual = d_ref_qualifier (di, NULL);
+    }
 
   *pret = d_prefix (di, 1);
   if (*pret == NULL)
@@ -4427,6 +4444,7 @@ d_count_templates_scopes (struct d_print
     case DEMANGLE_COMPONENT_CONST_THIS:
     case DEMANGLE_COMPONENT_REFERENCE_THIS:
     case DEMANGLE_COMPONENT_RVALUE_REFERENCE_THIS:
+    case DEMANGLE_COMPONENT_XOBJ_MEMBER_FUNCTION:
     case DEMANGLE_COMPONENT_TRANSACTION_SAFE:
     case DEMANGLE_COMPONENT_NOEXCEPT:
     case DEMANGLE_COMPONENT_THROW_SPEC:
@@ -6521,6 +6539,8 @@ d_print_mod (struct d_print_info *dpi, i
     case DEMANGLE_COMPONENT_RVALUE_REFERENCE:
       d_append_string (dpi, "&&");
       return;
+    case DEMANGLE_COMPONENT_XOBJ_MEMBER_FUNCTION:
+      return;
     case DEMANGLE_COMPONENT_COMPLEX:
       d_append_string (dpi, " _Complex");
       return;
@@ -6559,11 +6579,13 @@ d_print_function_type (struct d_print_in
 {
   int need_paren;
   int need_space;
+  int xobj_memfn;
   struct d_print_mod *p;
   struct d_print_mod *hold_modifiers;
 
   need_paren = 0;
   need_space = 0;
+  xobj_memfn = 0;
   for (p = mods; p != NULL; p = p->next)
     {
       if (p->printed)
@@ -6586,7 +6608,8 @@ d_print_function_type (struct d_print_in
 	  need_space = 1;
 	  need_paren = 1;
 	  break;
-	FNQUAL_COMPONENT_CASE:
+	case DEMANGLE_COMPONENT_XOBJ_MEMBER_FUNCTION:
+	  xobj_memfn = 1;
 	  break;
 	default:
 	  break;
@@ -6617,6 +6640,8 @@ d_print_function_type (struct d_print_in
     d_append_char (dpi, ')');
 
   d_append_char (dpi, '(');
+  if (xobj_memfn)
+    d_append_string (dpi, "this ");
 
   if (d_right (dc) != NULL)
     d_print_comp (dpi, options, d_right (dc));
--- libiberty/testsuite/demangle-expected.jj	2023-12-03 17:44:57.266453553 +0100
+++ libiberty/testsuite/demangle-expected	2024-01-12 12:22:56.647587418 +0100
@@ -1700,3 +1700,12 @@ void f<int>() requires C<int>
 # requires after ()
 _Z1fIiEvvQ1CIT_E
 void f<int>() requires C<int>
+
+_ZNH1S3fooES_
+S::foo(this S)
+
+_ZNH1S3barILi5EiEEvS_T0_
+void S::bar<5, int>(this S, int)
+
+_ZNH1S3bazERKS_
+S::baz(this S const&)
