diff --git a/NEWS b/NEWS
index 79c895e382..9e59cde737 100644
--- a/NEWS
+++ b/NEWS
@@ -9,11 +9,16 @@ Version 2.35
 
 Major new features:
 
-  [Add new features here]
+* Bump r_version in the debugger interface to 2 and add a new field,
+  r_next, support multiple namespaces.
 
 Deprecated and removed features, and other changes affecting compatibility:
 
-  [Add deprecations, removals and changes affecting compatibility here]
+* The r_version update in the debugger interface makes the glibc binary
+  incompatible with GDB binaries built without the following commits:
+
+  c0154a4a21a gdb: Don't assume r_ldsomap when r_version > 1 on Linux
+  4eb629d50d4 gdbserver: Check r_version < 1 for Linux debugger interface
 
 Changes to build and runtime requirements:
 
diff --git a/csu/Makefile b/csu/Makefile
index 3054329cea..e2390e4a7d 100644
--- a/csu/Makefile
+++ b/csu/Makefile
@@ -88,6 +88,9 @@ endif
 before-compile += $(objpfx)abi-tag.h
 generated += abi-tag.h
 
+# Put it here to generate it earlier.
+gen-as-const-headers += rtld-sizes.sym
+
 # These are the special initializer/finalizer files.  They are always the
 # first and last file in the link.  crti.o ... crtn.o define the global
 # "functions" _init and _fini to run the .init and .fini sections.
diff --git a/csu/rtld-sizes.sym b/csu/rtld-sizes.sym
new file mode 100644
index 0000000000..40dd8edaec
--- /dev/null
+++ b/csu/rtld-sizes.sym
@@ -0,0 +1,4 @@
+#include <link.h>
+
+--
+COMPAT_R_DEBUG_SIZE	sizeof (struct r_debug)
diff --git a/elf/Makefile b/elf/Makefile
index 725537c40b..1444a53405 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -35,7 +35,8 @@ dl-routines	= $(addprefix dl-,load lookup object reloc deps \
 				  execstack open close trampoline \
 				  exception sort-maps lookup-direct \
 				  call-libc-early-init write \
-				  thread_gscope_wait tls_init_tp)
+				  thread_gscope_wait tls_init_tp \
+				  debug-symbols)
 ifeq (yes,$(use-ldconfig))
 dl-routines += dl-cache
 endif
@@ -203,7 +204,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-tls16 tst-tls17 tst-tls18 tst-tls19 tst-tls-dlinfo \
 	 tst-align tst-align2 \
 	 tst-dlmodcount tst-dlopenrpath tst-deep1 \
-	 tst-dlmopen1 tst-dlmopen3 \
+	 tst-dlmopen1 tst-dlmopen3 tst-dlmopen4 \
 	 unload3 unload4 unload5 unload6 unload7 unload8 tst-global1 order2 \
 	 tst-audit1 tst-audit2 tst-audit8 tst-audit9 \
 	 tst-addr1 tst-thrlock \
@@ -672,6 +673,21 @@ LC_ALL=C sed $(ldd-rewrite) < $< \
 endef
 endif
 
+ifeq ($(build-shared),yes)
+generated += dl-debug-compat-symbols.os dl-debug-compat-symbols.o
+
+libof-dl-debug-compat-symbols = rtld
+
+$(objpfx)dl-debug-compat-symbols.os: dl-debug-symbols-gen.c
+	$(compile-command.c) -S
+
+$(objpfx)dl-debug-compat-symbols.o: dl-debug-symbols-gen.c
+	$(compile-command.c) -S
+
+$(objpfx)dl-debug-symbols.os: $(objpfx)dl-debug-compat-symbols.os
+$(objpfx)dl-debug-symbols.o: $(objpfx)dl-debug-compat-symbols.o
+endif
+
 $(objpfx)ldd: ldd.bash.in $(common-objpfx)soversions.mk \
 	      $(common-objpfx)config.make
 	$(gen-ldd)
@@ -1242,6 +1258,8 @@ $(objpfx)tst-dlmopen2.out: $(objpfx)tst-dlmopen1mod.so
 
 $(objpfx)tst-dlmopen3.out: $(objpfx)tst-dlmopen1mod.so
 
+$(objpfx)tst-dlmopen4.out: $(objpfx)tst-dlmopen1mod.so
+
 $(objpfx)tst-audit1.out: $(objpfx)tst-auditmod1.so
 tst-audit1-ENV = LD_AUDIT=$(objpfx)tst-auditmod1.so
 
diff --git a/elf/dl-close.c b/elf/dl-close.c
index f39001cab9..f9cddf90e2 100644
--- a/elf/dl-close.c
+++ b/elf/dl-close.c
@@ -500,7 +500,7 @@ _dl_close_worker (struct link_map *map, bool force)
 #endif
 
   /* Notify the debugger we are about to remove some loaded objects.  */
-  struct r_debug *r = _dl_debug_initialize (0, nsid);
+  struct r_debug_extended *r = _dl_debug_initialize (0, nsid);
   r->r_state = RT_DELETE;
   _dl_debug_state ();
   LIBC_PROBE (unmap_start, 2, nsid, r);
@@ -709,6 +709,27 @@ _dl_close_worker (struct link_map *map, bool force)
 	      assert (nsid != LM_ID_BASE);
 	      ns->_ns_loaded = imap->l_next;
 
+	      if (ns->_ns_loaded == NULL)
+		{
+		  /* Remove the empty namespace from the namespace linked
+		     list.  */
+		  struct r_debug_extended **pp, *p;
+
+		  for (pp = &_r_debug_extended.r_next;
+		       (p = *pp) != NULL;
+		       pp = &p->r_next)
+		    if (p == &ns->_ns_debug)
+		      {
+			/* Remove the empty namespace.  */
+			*pp = p->r_next;
+
+			/* Clear r_version to indicate that it is
+			   unused.  */
+			p->r_version = 0;
+			break;
+		      }
+		}
+
 	      /* Update the pointer to the head of the list
 		 we leave for debuggers to examine.  */
 	      r->r_map = (void *) ns->_ns_loaded;
diff --git a/elf/dl-debug-symbols-gen.c b/elf/dl-debug-symbols-gen.c
new file mode 100644
index 0000000000..2406260bcb
--- /dev/null
+++ b/elf/dl-debug-symbols-gen.c
@@ -0,0 +1,24 @@
+/* Generate the _r_debug_extended symbol used to communicate dynamic
+   linker state to the debugger at runtime.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <link.h>
+
+/* This structure communicates dl state to the debugger.  The debugger
+   finds it via the DT_DEBUG entry in the dynamic section.  */
+struct r_debug_extended _r_debug_extended;
diff --git a/elf/dl-debug-symbols.S b/elf/dl-debug-symbols.S
new file mode 100644
index 0000000000..0966b172ab
--- /dev/null
+++ b/elf/dl-debug-symbols.S
@@ -0,0 +1,31 @@
+/* Define symbols used to communicate dynamic linker state to the
+   debugger at runtime.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <rtld-sizes.h>
+
+#ifdef SHARED
+# include "dl-debug-compat-symbols.os"
+#else
+# include "dl-debug-compat-symbols.o"
+#endif
+
+/* Define the compatibility symbol, _r_debug, with size of struct r_debug,
+   as an alias of _r_debug_extended.  */
+declare_object_symbol_alias (_r_debug, _r_debug_extended,
+			     COMPAT_R_DEBUG_SIZE);
diff --git a/elf/dl-debug.c b/elf/dl-debug.c
index 2cd5f09753..9137d59da4 100644
--- a/elf/dl-debug.c
+++ b/elf/dl-debug.c
@@ -30,36 +30,42 @@ extern const int verify_link_map_members[(VERIFY_MEMBER (l_addr)
 					  && VERIFY_MEMBER (l_prev))
 					 ? 1 : -1];
 
-/* This structure communicates dl state to the debugger.  The debugger
-   normally finds it via the DT_DEBUG entry in the dynamic section, but in
-   a statically-linked program there is no dynamic section for the debugger
-   to examine and it looks for this particular symbol name.  */
-struct r_debug _r_debug;
+/* Initialize _r_debug_extended if it has not already been done.  The
+   argument is the run-time load address of the dynamic linker, to be
+   put in _r_debug_extended.r_ldbase.  Returns the address of
+   _r_debug_extended.  */
 
-
-/* Initialize _r_debug if it has not already been done.  The argument is
-   the run-time load address of the dynamic linker, to be put in
-   _r_debug.r_ldbase.  Returns the address of _r_debug.  */
-
-struct r_debug *
+struct r_debug_extended *
 _dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
 {
-  struct r_debug *r;
+  struct r_debug_extended *r;
 
   if (ns == LM_ID_BASE)
-    r = &_r_debug;
+    r = &_r_debug_extended;
   else
-    r = &GL(dl_ns)[ns]._ns_debug;
+    {
+      r = &GL(dl_ns)[ns]._ns_debug;
+      if (DL_NNS > 1 && r->r_version == 0)
+	{
+	  /* Add the new namespace to the linked list.  */
+	  r->r_next = _r_debug_extended.r_next;
+	  _r_debug_extended.r_next = r;
+	}
+    }
 
-  if (r->r_map == NULL || ldbase != 0)
+  if (r->r_version == 0)
     {
-      /* Tell the debugger where to find the map of loaded objects.  */
-      r->r_version = 1	/* R_DEBUG_VERSION XXX */;
-      r->r_ldbase = ldbase ?: _r_debug.r_ldbase;
-      r->r_map = (void *) GL(dl_ns)[ns]._ns_loaded;
+      /* Tell the debugger where to find the map of loaded objects.
+	 Bump r_version to 2 for the r_next field.  */
+      r->r_version = 2;
+      r->r_ldbase = ldbase ?: _r_debug_extended.r_ldbase;
       r->r_brk = (ElfW(Addr)) &_dl_debug_state;
+      r->r_next = NULL;
     }
 
+  if (r->r_map == NULL)
+    r->r_map = (void *) GL(dl_ns)[ns]._ns_loaded;
+
   return r;
 }
 
diff --git a/elf/dl-load.c b/elf/dl-load.c
index dc911e326a..aab290bea6 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -949,7 +949,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
   /* Initialize to keep the compiler happy.  */
   const char *errstring = NULL;
   int errval = 0;
-  struct r_debug *r = _dl_debug_initialize (0, nsid);
+  struct r_debug_extended *r = _dl_debug_initialize (0, nsid);
   bool make_consistent = false;
 
   /* Get file information.  To match the kernel behavior, do not fill
diff --git a/elf/dl-open.c b/elf/dl-open.c
index 98f8bf81b3..5c54df5b7f 100644
--- a/elf/dl-open.c
+++ b/elf/dl-open.c
@@ -630,7 +630,7 @@ dl_open_worker (void *a)
 #endif
 
   /* Notify the debugger all new objects are now ready to go.  */
-  struct r_debug *r = _dl_debug_initialize (0, args->nsid);
+  struct r_debug_extended *r = _dl_debug_initialize (0, args->nsid);
   r->r_state = RT_CONSISTENT;
   _dl_debug_state ();
   LIBC_PROBE (map_complete, 3, args->nsid, r, new);
diff --git a/elf/dl-reloc-static-pie.c b/elf/dl-reloc-static-pie.c
index d5bd2f31e9..bb1687d3d9 100644
--- a/elf/dl-reloc-static-pie.c
+++ b/elf/dl-reloc-static-pie.c
@@ -51,8 +51,8 @@ _dl_relocate_static_pie (void)
   ELF_DYNAMIC_RELOCATE (main_map, 0, 0, 0);
   main_map->l_relocated = 1;
 
-  /* Initialize _r_debug.  */
-  struct r_debug *r = _dl_debug_initialize (0, LM_ID_BASE);
+  /* Initialize _r_debug_extended.  */
+  struct r_debug_extended *r = _dl_debug_initialize (0, LM_ID_BASE);
   r->r_state = RT_CONSISTENT;
 
   /* Set up debugging before the debugger is notified for the first
diff --git a/elf/link.h b/elf/link.h
index ff3a85c847..60110f74bc 100644
--- a/elf/link.h
+++ b/elf/link.h
@@ -34,14 +34,20 @@
 #include <bits/elfclass.h>		/* Defines __ELF_NATIVE_CLASS.  */
 #include <bits/link.h>
 
-/* Rendezvous structure used by the run-time dynamic linker to communicate
-   details of shared object loading to the debugger.  If the executable's
-   dynamic section has a DT_DEBUG element, the run-time linker sets that
-   element's value to the address where this structure can be found.  */
+enum r_debug_state
+  {
+    RT_CONSISTENT,	/* Mapping change is complete.  */
+    RT_ADD,		/* Beginning to add a new object.  */
+    RT_DELETE		/* Beginning to remove an object mapping.  */
+  };
+
+/* The legacy rendezvous structure used by the run-time dynamic linker to
+   communicate details of shared object loading to the debugger.  */
 
 struct r_debug
   {
-    int r_version;		/* Version number for this protocol.  */
+    /* Version number for this protocol.  It should be greater than 0.  */
+    int r_version;
 
     struct link_map *r_map;	/* Head of the chain of loaded objects.  */
 
@@ -51,28 +57,57 @@ struct r_debug
        The debugger can set a breakpoint at this address if it wants to
        notice shared object mapping changes.  */
     ElfW(Addr) r_brk;
-    enum
-      {
-	/* This state value describes the mapping change taking place when
-	   the `r_brk' address is called.  */
-	RT_CONSISTENT,		/* Mapping change is complete.  */
-	RT_ADD,			/* Beginning to add a new object.  */
-	RT_DELETE		/* Beginning to remove an object mapping.  */
-      } r_state;
+    /* This state value describes the mapping change taking place when
+       the `r_brk' address is called.  */
+    enum r_debug_state r_state;
 
     ElfW(Addr) r_ldbase;	/* Base address the linker is loaded at.  */
   };
 
-/* This is the instance of that structure used by the dynamic linker.  */
+/* This is the compatibility symbol of that structure provided by the
+   dynamic linker.  */
 extern struct r_debug _r_debug;
 
+/* The extended rendezvous structure used by the run-time dynamic linker
+   to communicate details of shared object loading to the debugger.  If
+   the executable's dynamic section has a DT_DEBUG element, the run-time
+   linker sets that element's value to the address where this structure
+   can be found.  */
+
+struct r_debug_extended
+  {
+    /* Version number for this protocol.  It should be greater than 0.  */
+    int r_version;
+
+    struct link_map *r_map;	/* Head of the chain of loaded objects.  */
+
+    /* This is the address of a function internal to the run-time linker,
+       that will always be called when the linker begins to map in a
+       library or unmap it, and again when the mapping change is complete.
+       The debugger can set a breakpoint at this address if it wants to
+       notice shared object mapping changes.  */
+    ElfW(Addr) r_brk;
+    /* This state value describes the mapping change taking place when
+       the `r_brk' address is called.  */
+    enum r_debug_state r_state;
+
+    ElfW(Addr) r_ldbase;	/* Base address the linker is loaded at.  */
+
+    /* The following field is added by r_version == 2.  */
+
+    /* Link to the next r_debug_extended structure.  Each r_debug_extended
+       structure represents a different namespace.  The first
+       r_debug_extended structure is for the default namespace.  */
+    struct r_debug_extended *r_next;
+  };
+
 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
    of whatever module refers to `_DYNAMIC'.  So, to find its own
-   `struct r_debug', a program could do:
+   `struct r_debug_extended', a program could do:
      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
        if (dyn->d_tag == DT_DEBUG)
-	 r_debug = (struct r_debug *) dyn->d_un.d_ptr;
-   */
+	 r_debug_extended = (struct r_debug_extended *) dyn->d_un.d_ptr;
+ */
 extern ElfW(Dyn) _DYNAMIC[];
 
 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
diff --git a/elf/rtld-debugger-interface.txt b/elf/rtld-debugger-interface.txt
index 61bc99e4b0..f6aaa28706 100644
--- a/elf/rtld-debugger-interface.txt
+++ b/elf/rtld-debugger-interface.txt
@@ -9,6 +9,9 @@ structure can be found.
 
 The r_debug structure contains (amongst others) the following fields:
 
+  int r_version:
+    Version number for this protocol.  It should be greater than 0.
+
   struct link_map *r_map:
     A linked list of loaded objects.
 
@@ -32,6 +35,17 @@ but there is no way for the debugger to discover whether any of the
 objects in the link-map have been relocated or not.
 
 
+Extension to the r_debug structure
+==================================
+
+The r_debug_extended structure is an extension of the r_debug interface.
+If r_version is 2, one additional field is available:
+
+  struct r_debug_extended *r_next;
+    Link to the next r_debug_extended structure.  Each r_debug_extended
+    structure represents a different namespace.  The first r_debug_extended
+    structure is for the default namespace.
+
 Probe-based debugger interface
 ==============================
 
diff --git a/elf/rtld.c b/elf/rtld.c
index 878e6480f4..17bb1262fb 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -1660,9 +1660,9 @@ dl_main (const ElfW(Phdr) *phdr,
      objects.  */
   call_init_paths (&state);
 
-  /* Initialize _r_debug.  */
-  struct r_debug *r = _dl_debug_initialize (GL(dl_rtld_map).l_addr,
-					    LM_ID_BASE);
+  /* Initialize _r_debug_extended.  */
+  struct r_debug_extended *r
+    = _dl_debug_initialize (GL(dl_rtld_map).l_addr, LM_ID_BASE);
   r->r_state = RT_CONSISTENT;
 
   /* Put the link_map for ourselves on the chain so it can be found by
diff --git a/elf/tst-dlmopen4.c b/elf/tst-dlmopen4.c
new file mode 100644
index 0000000000..936e180f5e
--- /dev/null
+++ b/elf/tst-dlmopen4.c
@@ -0,0 +1,68 @@
+/* Test struct r_debug_extended via DT_DEBUG.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <link.h>
+#include <stdlib.h>
+#include <string.h>
+#include <gnu/lib-names.h>
+#include <support/xdlfcn.h>
+#include <support/check.h>
+#include <support/test-driver.h>
+
+#ifndef ELF_MACHINE_GET_R_DEBUG
+# define ELF_MACHINE_GET_R_DEBUG(d) \
+    (__extension__ ({ 						\
+      struct r_debug_extended *debug;				\
+      if ((d)->d_tag == DT_DEBUG)				\
+	debug = (struct r_debug_extended *) (d)->d_un.d_ptr;	\
+      else							\
+	debug = NULL;						\
+      debug; }))
+#endif
+
+static int
+do_test (void)
+{
+  void *h = xdlmopen (LM_ID_NEWLM, "$ORIGIN/tst-dlmopen1mod.so",
+		      RTLD_LAZY);
+
+  int status = EXIT_FAILURE;
+  ElfW(Dyn) *d;
+  for (d = _DYNAMIC; d->d_tag != DT_NULL; ++d)
+    {
+      struct r_debug_extended *debug = ELF_MACHINE_GET_R_DEBUG (d);
+      if (debug != NULL)
+	{
+	  TEST_VERIFY_EXIT (debug->r_version == 2);
+	  TEST_VERIFY_EXIT (debug->r_next != NULL);
+	  TEST_VERIFY_EXIT (debug->r_next->r_next == NULL);
+	  TEST_VERIFY_EXIT (debug->r_next->r_map != NULL);
+	  TEST_VERIFY_EXIT (debug->r_next->r_map->l_name != NULL);
+	  const char *name = basename (debug->r_next->r_map->l_name);
+	  TEST_VERIFY_EXIT (strcmp (name, "tst-dlmopen1mod.so") == 0);
+	  status = EXIT_SUCCESS;
+	}
+    }
+
+  xdlclose (h);
+
+  return status;
+}
+
+#include <support/test-driver.c>
diff --git a/include/link.h b/include/link.h
index 4af16cb596..7b8250db36 100644
--- a/include/link.h
+++ b/include/link.h
@@ -353,6 +353,10 @@ struct auditstate
 };
 
 
+/* This is the hidden instance of struct r_debug_extended used by the
+   dynamic linker.  */
+extern struct r_debug_extended _r_debug_extended attribute_hidden;
+
 #if __ELF_NATIVE_CLASS == 32
 # define symbind symbind32
 #elif __ELF_NATIVE_CLASS == 64
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 9c15259236..a37b3fec82 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -355,7 +355,7 @@ struct rtld_global
       void (*free) (void *);
     } _ns_unique_sym_table;
     /* Keep track of changes to each namespace' list.  */
-    struct r_debug _ns_debug;
+    struct r_debug_extended _ns_debug;
   } _dl_ns[DL_NNS];
   /* One higher than index of last used namespace.  */
   EXTERN size_t _dl_nns;
@@ -1096,7 +1096,8 @@ rtld_hidden_proto (_dl_debug_state)
 /* Initialize `struct r_debug' if it has not already been done.  The
    argument is the run-time load address of the dynamic linker, to be put
    in the `r_ldbase' member.  Returns the address of the structure.  */
-extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
+extern struct r_debug_extended *_dl_debug_initialize (ElfW(Addr) ldbase,
+						      Lmid_t ns)
      attribute_hidden;
 
 /* Initialize the basic data structure for the search paths.  SOURCE
