[gdb/symtab] Fix incorrect filenames with inter-CU refs

With target board unix we get:
...
$ gdb -q -batch outputs/gdb.cp/cplusfuncs/cplusfuncs \
  -ex "info function operator\*"
All functions matching regular expression "operator\*":

File /home/vries/gdb/src/gdb/testsuite/gdb.cp/cplusfuncs.cc:
72:     void foo::operator*(foo&);
85:     void foo::operator*=(foo&);
...
but with target board cc-with-dwz-m:
...
All functions matching regular expression "operator\*":

File /usr/lib/gcc/aarch64-redhat-linux/14/include/stddef.h:
72:     void foo::operator*(foo&);
85:     void foo::operator*=(foo&);
...

The first operator:
...
$ c++filt _ZN3foomlERS_
foo::operator*(foo&)
...
matches address 0x410250 which is defined here in the CU in the exec:
...
 <1><10f1>: Abbrev Number: 13 (DW_TAG_subprogram)
    <10f2>   DW_AT_specification: <alt 0x93>
    <10f6>   DW_AT_decl_line   : 72
    <10f7>   DW_AT_decl_column : 7
    <10f7>   DW_AT_object_pointer: <0x1106>
    <10f9>   DW_AT_low_pc      : 0x410250
    <1101>   DW_AT_high_pc     : 32
    <1102>   DW_AT_frame_base  : 1 byte block: 9c       (DW_OP_call_frame_cfa)
    <1104>   DW_AT_call_all_calls: 1
...
and declared here in the PU in the .dwz file:
...
 <2><93>: Abbrev Number: 20 (DW_TAG_subprogram)
    <94>   DW_AT_external    : 1
    <94>   DW_AT_name        : operator*
    <98>   DW_AT_decl_file   : 2
    <98>   DW_AT_decl_line   : 10
    <99>   DW_AT_decl_column : 9
    <9a>   DW_AT_linkage_name: _ZN3foomlERS_
    <9e>   DW_AT_accessibility: 1       (public)
    <9e>   DW_AT_declaration : 1
    <9e>   DW_AT_object_pointer: <0xa2>
...

When creating a new symbol for the operator, the DW_AT_decl_file attribute is
looked up, and found to be 2.

The 2 is supposed to be mapped using the PU, which has this file name table:
...
 The File Name Table (offset 0x78, lines 3, columns 2):
  Entry Dir     Name
  0     0       <dwz>
  1     1       stddef.h
  2     2       cplusfuncs.cc
...

Instead, it's mapped using the CU, which has this file name table:
...
 The File Name Table (offset 0x34, lines 3, columns 2):
  Entry Dir     Name
  0     1       cplusfuncs.cc
  1     1       cplusfuncs.cc
  2     2       stddef.h
...

This is PR symtab/30814.  There's a similar PR for lto, PR symtab/25771, where
the same problem happens for two CUs.

Fix this by using the correct file name table.

Add a dwarf assembly test-case for PR25771.

Tested on aarch64-linux.

Reviewed-By: Tom Tromey <tom@tromey.com>

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=25771
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30814

2 files changed, 96 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-inter-cu-symbol.exp b/gdb/testsuite/gdb.dwarf2/dw2-inter-cu-symbol.exp
new file mode 100644
index 0000000..13a6993
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-inter-cu-symbol.exp
@@ -0,0 +1,92 @@
+# Copyright 2024 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.
+require dwarf2_support
+
+standard_testfile main.c -dw.S
+
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    global srcdir subdir srcfile srcfile2
+    declare_labels var_label int_label L1 L2
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {stmt_list $L1 DW_FORM_sec_offset}
+	} {
+	    tag_variable {
+		{name var1}
+		{abstract_origin %$var_label}
+		{const_value 1 DW_FORM_sdata}
+	    }
+	    subprogram {
+		{external 1 flag}
+		{MACRO_AT_func {main}}
+	    }
+	    int_label: base_type {
+		{byte_size 4 udata}
+		{encoding @DW_ATE_signed}
+		{name int}
+	    }
+	}
+    }
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {stmt_list $L2 DW_FORM_sec_offset}
+	} {
+	    var_label: tag_variable {
+		{name "var1"}
+		{type %$int_label}
+		{decl_file 1}
+		{decl_line 1}
+	    }
+	}
+    }
+
+    lines {version 2} L1 {
+	file_name "file1.c" 0
+	file_name "file2.c" 0
+    }
+
+    lines {version 2} L2 {
+	file_name "file3.c" 0
+	file_name "file4.c" 0
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+if ![runto main] {
+    return -1
+}
+
+gdb_test "p var1" " = 1"
+
+set re \
+    [multi_line \
+	 "All variables matching regular expression \"var1\":" \
+	 "" \
+	 "File file3.c:" \
+	 "1:\tstatic int var1;"]
+gdb_test "info var var1" $re
diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index f9be6c4..6a5afec 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -887,6 +887,10 @@ namespace eval Dwarf {
 	    DW_AT_GNU_addr_base {
 		return DW_FORM_sec_offset
 	    }
+	    DW_AT_decl_file -
+	    DW_AT_decl_line {
+		return DW_FORM_udata
+	    }
 	}
 	return ""
     }