[gdb/testsuite] Add gdb.dwarf2/debug-names-bad-cu-index.exp

Add test-case gdb.dwarf2/debug-names-bad-cu-index.exp, a regression test for
commit 2fe9a3c41fa ("[gdb/symtab] Fix bad compile unit index complaint").

Tested on x86_64-linux.

gdb/testsuite/gdb.dwarf2/debug-names-bad-cu-index.exp

@@ -0,0 +1,90 @@
+# 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 $_start_end DW_FORM_addr}
+	    }
+	}
+    }
+
+    tu { label tu_label } 0x8ece66f4224fddb3 "" {
+	type_unit {} {
+	    declare_labels int_type
+
+	    structure_type {
+		{name struct_with_int_member}
+		{byte_size 4 sdata}
+	    } {
+		member {
+		    {name member}
+		    {type :$int_type}
+		}
+	    }
+	    int_type: base_type {
+		{name int}
+		{encoding @DW_ATE_signed}
+		{byte_size 4 sdata}
+	    }
+	}
+    }
+
+    debug_names {} {
+	cu cu_label
+	tu tu_label
+	name _start subprogram CU-1 0xEDDB6232
+	name struct_with_int_member structure_type tu_label 0x53A2AE86
+    }
+}
+
+if [prepare_for_testing "failed to prepare" $testfile "${asm_file} ${srcfile}" \
+	[list additional_flags=-nostartfiles]] {
+    return -1
+}
+
+# Verify that .debug_names section is not ignored.
+set index [have_index $binfile]
+gdb_assert { [string equal $index "debug_names"] } ".debug_names used"
+
+set re "During symbol reading: .debug_names entry has bad CU index 1 "
+with_complaints 1 {
+    gdb_test "p _start" "$re.*"
+}

gdb/testsuite/lib/dwarf.exp

@@ -2957,6 +2957,8 @@ namespace eval Dwarf {
     #     -- add a name.
 
     proc debug_names { options body } {
+	global decimal
+
 	parse_options {
 	    { is_64 0 }
 	    { version 5 }
@@ -3111,6 +3113,13 @@ namespace eval Dwarf {
 	    set tag [lindex $idx 1]
 	    set cu [lindex $idx 2]
 
+	    if { [regexp "^CU-($decimal)$" $cu dummy cu_index] } {
+		set attr_name compile_unit
+		set attr_val 1
+	    } elseif { [regexp "^TU-($decimal)$" $cu dummy cu_index] } {
+		set attr_name type_unit
+		set attr_val 2
+	    } else {
 		set cu_index [lsearch -exact $_debug_names_cus $cu]
 		if { $cu_index == -1 } {
 		    set attr_name type_unit
@@ -3119,6 +3128,7 @@ namespace eval Dwarf {
 		    set attr_name compile_unit
 		    set attr_val 1
 		}
+	    }
 
 	    _op .byte $abbrev "abbrev $abbrev"
 	    _op .uleb128 $_constants(DW_TAG_$tag) "DW_TAG_$tag"
@@ -3138,6 +3148,11 @@ namespace eval Dwarf {
 	    set cu [lindex $idx 2]
 	    set label [lindex $idx 4]
 
+	    if { [regexp "^CU-($decimal)$" $cu dummy cu_index] } {
+		set comment "$name: CU index"
+	    } elseif { [regexp "^TU-($decimal)$" $cu dummy cu_index] } {
+		set comment "$name: TU index"
+	    } else {
 		set cu_index [lsearch -exact $_debug_names_cus $cu]
 		if { $cu_index == -1 } {
 		    set cu_index [lsearch -exact $_debug_names_tus $cu]
@@ -3145,6 +3160,7 @@ namespace eval Dwarf {
 		} else {
 		    set comment "$name: CU index"
 		}
+	    }
 	    define_label $label
 	    _op .byte $abbrev "$name: abbrev"
 	    _op .uleb128 $cu_index $comment