[gdb/symtab] Fix assert in read_addrmap_from_aranges

When loading the debug-names-duplicate-cu executable included in this
test-case, we run into:
...
(gdb) file debug-names-duplicate-cu^M
Reading symbols from debug-names-duplicate-cu...^M
src/gdb/dwarf2/read.c:2353: internal-error: read_addrmap_from_aranges: \
  Assertion `insertpair.second' failed.^M
...

This assert was added in recent commit 75337cbc14 ("[gdb/symtab] Fix
.debug_aranges duplicate offset warning").

The assert triggers because the CU table in the .debug_names section contains
a duplicate:
...
Version 5
Augmentation string: 47 44 42 00  ("GDB")
CU table:
[  0] 0x0
[  1] 0x0
...

Fix this by rejecting the .debug_names index:
...
(gdb) file debug-names-duplicate-cu^M
Reading symbols from debug-names-duplicate-cu...^M
warning: Section .debug_names has duplicate entry in CU table, \
  ignoring .debug_names.^M
...

Likewise for the case where the CU table is not sorted by increasing offset.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29436

gdb/dwarf2/read.c

@@ -4599,7 +4599,7 @@ read_debug_names_from_section (struct objfile *objfile,
 /* A helper for create_cus_from_debug_names that handles the MAP's CU
    list.  */
 
-static void
+static bool
 create_cus_from_debug_names_list (dwarf2_per_bfd *per_bfd,
 				  const mapped_debug_names &map,
 				  dwarf2_section_info &section,
@@ -4624,7 +4624,7 @@ create_cus_from_debug_names_list (dwarf2_per_bfd *per_bfd,
 					 sect_off, 0);
 	  per_bfd->all_comp_units.push_back (std::move (per_cu));
 	}
-      return;
+      return true;
     }
 
   sect_offset sect_off_prev;
@@ -4643,6 +4643,18 @@ create_cus_from_debug_names_list (dwarf2_per_bfd *per_bfd,
 	sect_off_next = (sect_offset) section.size;
       if (i >= 1)
 	{
+	  if (sect_off_next == sect_off_prev)
+	    {
+	      warning (_("Section .debug_names has duplicate entry in CU table,"
+			 " ignoring .debug_names."));
+	      return false;
+	    }
+	  if (sect_off_next < sect_off_prev)
+	    {
+	      warning (_("Section .debug_names has non-ascending CU table,"
+			 " ignoring .debug_names."));
+	      return false;
+	    }
 	  const ULONGEST length = sect_off_next - sect_off_prev;
 	  dwarf2_per_cu_data_up per_cu
 	    = create_cu_from_index_list (per_bfd, &section, is_dwz,
@@ -4651,12 +4663,14 @@ create_cus_from_debug_names_list (dwarf2_per_bfd *per_bfd,
 	}
       sect_off_prev = sect_off_next;
     }
+
+  return true;
 }
 
 /* Read the CU list from the mapped index, and use it to create all
    the CU objects for this dwarf2_per_objfile.  */
 
-static void
+static bool
 create_cus_from_debug_names (dwarf2_per_bfd *per_bfd,
 			     const mapped_debug_names &map,
 			     const mapped_debug_names &dwz_map)
@@ -4664,15 +4678,16 @@ create_cus_from_debug_names (dwarf2_per_bfd *per_bfd,
   gdb_assert (per_bfd->all_comp_units.empty ());
   per_bfd->all_comp_units.reserve (map.cu_count + dwz_map.cu_count);
 
-  create_cus_from_debug_names_list (per_bfd, map, per_bfd->info,
+  if (!create_cus_from_debug_names_list (per_bfd, map, per_bfd->info,
-				    false /* is_dwz */);
+					 false /* is_dwz */))
+    return false;
 
   if (dwz_map.cu_count == 0)
-    return;
+    return true;
 
   dwz_file *dwz = dwarf2_get_dwz_file (per_bfd);
-  create_cus_from_debug_names_list (per_bfd, dwz_map, dwz->info,
+  return create_cus_from_debug_names_list (per_bfd, dwz_map, dwz->info,
-				    true /* is_dwz */);
+					   true /* is_dwz */);
 }
 
 /* Read .debug_names.  If everything went ok, initialize the "quick"
@@ -4709,7 +4724,11 @@ dwarf2_read_debug_names (dwarf2_per_objfile *per_objfile)
 	}
     }
 
-  create_cus_from_debug_names (per_bfd, *map, dwz_map);
+  if (!create_cus_from_debug_names (per_bfd, *map, dwz_map))
+    {
+      per_bfd->all_comp_units.clear ();
+      return false;
+    }
 
   if (map->tu_count != 0)
     {

gdb/testsuite/gdb.dwarf2/debug-names-duplicate-cu.exp

@@ -0,0 +1,78 @@
+# Copyright 2022 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+}
+
+standard_testfile _start.c debug-names.S
+
+set func_info_vars \
+    [get_func_info _start [list debug additional_flags=-nostartfiles]]
+
+# Create the DWARF.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble {
+    filename $asm_file
+    add_dummy_cus 0
+} {
+    global func_info_vars
+    foreach var $func_info_vars {
+	global $var
+    }
+
+    cu { label cu_label } {
+	compile_unit {{language @DW_LANG_C}} {
+	    subprogram {
+		{DW_AT_name _start}
+		{DW_AT_low_pc $_start_start DW_FORM_addr}
+		{DW_AT_high_pc $_start_end DW_FORM_addr}
+	    }
+	    base_type {
+		{name int}
+		{byte_size 4 sdata}
+		{encoding @DW_ATE_signed}
+	    }
+	}
+    }
+
+    debug_names {} {
+	cu cu_label
+	cu cu_label
+	name _start subprogram cu_label 0xEDDB6232
+	name int base_type cu_label 0xB888030
+    }
+}
+
+if [prepare_for_testing "failed to prepare" $testfile "${asm_file} ${srcfile}" \
+	[list additional_flags=-nostartfiles]] {
+    return -1
+}
+
+# Check for warning.
+set re \
+    [list \
+	 "warning:" \
+	 "Section .debug_names has duplicate entry in CU table," \
+	 "ignoring .debug_names."]
+set re [join $re]
+gdb_assert {[regexp $re $gdb_file_cmd_msg]} "warning"
+
+# Verify that .debug_names section is ignored.
+set index [have_index $binfile]
+gdb_assert { [string equal $index ""] } ".debug_names not used"

gdb/testsuite/gdb.dwarf2/debug-names-non-ascending-cu.exp

@@ -0,0 +1,83 @@
+# Copyright 2022 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+}
+
+standard_testfile _start.c debug-names.S
+
+set func_info_vars \
+    [get_func_info _start [list debug additional_flags=-nostartfiles]]
+
+# Create the DWARF.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble {
+    filename $asm_file
+    add_dummy_cus 0
+} {
+    global func_info_vars
+    foreach var $func_info_vars {
+	global $var
+    }
+
+    cu { label cu_label } {
+	compile_unit {{language @DW_LANG_C}} {
+	    subprogram {
+		{DW_AT_name _start}
+		{DW_AT_low_pc $_start_start DW_FORM_addr}
+		{DW_AT_high_pc $_start_end DW_FORM_addr}
+	    }
+	}
+    }
+
+    cu { label cu_label_2 } {
+	compile_unit {{language @DW_LANG_C}} {
+	    base_type {
+		{name int}
+		{byte_size 4 sdata}
+		{encoding @DW_ATE_signed}
+	    }
+	}
+    }
+
+    debug_names {} {
+	cu cu_label_2
+	cu cu_label
+	name _start subprogram cu_label 0xEDDB6232
+	name int base_type cu_label 0xB888030
+    }
+}
+
+if [prepare_for_testing "failed to prepare" $testfile "${asm_file} ${srcfile}" \
+	[list additional_flags=-nostartfiles]] {
+    return -1
+}
+
+# Check for warning.
+set re \
+    [list \
+	 "warning:" \
+	 "Section .debug_names has non-ascending CU table," \
+	 "ignoring .debug_names."]
+set re [join $re]
+gdb_assert {[regexp $re $gdb_file_cmd_msg]} "warning"
+
+# Verify that .debug_names section is ignored.
+set index [have_index $binfile]
+gdb_assert { [string equal $index ""] } ".debug_names not used"