[gdb/symtab] Add symbol with inherited DW_AT_const_value to psymtabs

Consider the test-case added in this patch, with resulting dwarf (related to
variable aaa):
...
 <0><d2>: Abbrev Number: 2 (DW_TAG_partial_unit)
 <1><eb>: Abbrev Number: 4 (DW_TAG_variable)
    <ec>   DW_AT_name        : aaa
    <f0>   DW_AT_type        : <0xe4>
    <f4>   DW_AT_const_value : 1
 <0><10c>: Abbrev Number: 2 (DW_TAG_compile_unit)
    <10e>   DW_AT_name        : <artificial>
 <1><11b>: Abbrev Number: 3 (DW_TAG_variable)
    <11c>   DW_AT_abstract_origin: <0xeb>
...

When running the test-case, we see:
...
(gdb) p aaa^M
No symbol "aaa" in current context.^M
(gdb) FAIL: gdb.dwarf2/imported-unit-abstract-const-value.exp: p aaa
...
while with target board readnow.exp, we have:
...
(gdb) p aaa^M
$1 = 1^M
...

This is due to the fact that there's no aaa symbol in the partial symtabs:
...
Partial symtab for source file <artificial>@0x101 (object 0x351cf40)^M
   ...
Global partial symbols:^M
    `main', function, 0x4004a7^M
^M
...
which is due to the fact that when attempting to add the symbol corresponding
to DIE 0x11b in add_partial_symbol:
...
(gdb) p /x pdi->sect_off
$4 = 0x11b
(gdb) p pdi.has_const_value
$5 = 0
...
it seems the DW_AT_const_value was not inherited from DIE 0xeb, and
consequently we leave without adding a partial symbol.

Fix this by making sure that partial_die_info::has_const_value is inherited
in partial_die_info::fixup.

Build and reg-tested on x86_64-linux.

Tested test-case with target boards readnow, cc-with-gdb-index and
cc-with-debug-names.  The "print aaa" test fails for cc-with-gdb-index, that's
PR25791, the test passes when applying the corresponding proposed patch.

gdb/ChangeLog:

2020-04-07  Tom de Vries  <tdevries@suse.de>

	PR symtab/25796
	* dwarf2/read.c (can_have_DW_AT_const_value_p): New function.
	(partial_die_info::fixup): Inherit has_const_value.

gdb/testsuite/ChangeLog:

2020-04-07  Tom de Vries  <tdevries@suse.de>

	PR symtab/25796
	* gdb.dwarf2/imported-unit-abstract-const-value.exp: New file.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2020-04-07  Tom de Vries  <tdevries@suse.de>
+
+	PR symtab/25796
+	* dwarf2/read.c (can_have_DW_AT_const_value_p): New function.
+	(partial_die_info::fixup): Inherit has_const_value.
+
 2020-04-07  Tom de Vries  <tdevries@suse.de>
 
 	* psymtab.c (maintenance_check_psymtabs): Skip static LOC_BLOCK

gdb/dwarf2/read.c

@@ -18259,6 +18259,25 @@ guess_partial_die_structure_name (struct partial_die_info *struct_pdi,
     }
 }
 
+/* Return true if a DIE with TAG may have the DW_AT_const_value
+   attribute.  */
+
+static bool
+can_have_DW_AT_const_value_p (enum dwarf_tag tag)
+{
+  switch (tag)
+    {
+    case DW_TAG_constant:
+    case DW_TAG_enumerator:
+    case DW_TAG_formal_parameter:
+    case DW_TAG_template_value_param:
+    case DW_TAG_variable:
+      return true;
+    }
+
+  return false;
+}
+
 void
 partial_die_info::fixup (struct dwarf2_cu *cu)
 {
@@ -18291,6 +18310,24 @@ partial_die_info::fixup (struct dwarf2_cu *cu)
 	}
     }
 
+  if (!has_const_value && has_specification
+      && can_have_DW_AT_const_value_p (tag))
+    {
+      struct partial_die_info *spec_die;
+
+      auto res = find_partial_die (spec_offset, spec_is_dwz, cu);
+      spec_die = res.pdi;
+      cu = res.cu;
+
+      spec_die->fixup (cu);
+
+      if (spec_die->has_const_value)
+	{
+	  /* Copy DW_AT_const_value attribute if it is set.  */
+	  has_const_value = spec_die->has_const_value;
+	}
+    }
+
   /* Set default names for some unnamed DIEs.  */
 
   if (name == NULL && tag == DW_TAG_namespace)

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2020-04-07  Tom de Vries  <tdevries@suse.de>
+
+	PR symtab/25796
+	* gdb.dwarf2/imported-unit-abstract-const-value.exp: New file.
+
 2020-04-07  Tom de Vries  <tdevries@suse.de>
 
 	* gdb.base/check-psymtab.c: New test.

gdb/testsuite/gdb.dwarf2/imported-unit-abstract-const-value.exp

@@ -0,0 +1,98 @@
+# Copyright 2020 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/>.
+
+# Test that a concrete var importing an abstract var using
+# DW_AT_abstract_origin inherits the DW_AT_const_value attribute.
+
+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 main.c .S
+
+set executable ${testfile}
+set asm_file [standard_output_file ${srcfile2}]
+
+# We need to know the size of integer type in order
+# to write some of the debugging info we'd like to generate.
+if [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] {
+    return -1
+}
+
+# Create the DWARF.
+Dwarf::assemble $asm_file {
+    declare_labels cu_label main_label int_label
+    declare_labels aaa_label
+    set int_size [get_sizeof "int" 4]
+
+    global srcdir subdir srcfile
+
+    extern main
+
+    set main_range [function_range main ${srcdir}/${subdir}/${srcfile}]
+    set main_start [lindex $main_range 0]
+    set main_length [lindex $main_range 1]
+
+    cu {} {
+	cu_label: partial_unit {
+	    {language @DW_LANG_C}
+	    {name "imported_unit.c"}
+	} {
+	    int_label: base_type {
+		{byte_size $int_size sdata}
+		{encoding @DW_ATE_signed}
+		{name int}
+	    }
+
+	    aaa_label: DW_TAG_variable {
+		{name aaa}
+		{type :$int_label}
+		{const_value 1 DW_FORM_sdata}
+	    }
+
+	    main_label: subprogram {
+		{name main}
+		{type :$int_label}
+		{external 1 flag}
+	    }
+	}
+    }
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name "<artificial>"}
+	} {
+	    DW_TAG_variable {
+		{abstract_origin %$aaa_label}
+	    }
+	    subprogram {
+		{abstract_origin %$main_label}
+		{low_pc $main_start addr}
+		{high_pc "$main_start + $main_length" addr}
+	    }
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+gdb_test "p aaa" "= 1"