Finding data member in virtual base class

This patch fixes the original problem - printing member in a virtual base,
using various expressions, do not yield the same value. Simple test case
below demonstrates the problem:

% cat t.cc
struct base { int i; };
typedef base tbase;
struct derived: virtual tbase { void func() { } };
int main() { derived().func(); }
% g++ -g t.cc
% gdb a.out
(gdb) break derived::func
(gdb) run
(gdb) p i
$1 = 0
(gdb) p base::i
$3 = 0
(gdb) p derived::i
$4 = 4196392

To fix the problem, add function get_baseclass_offset() which searches
recursively for the base class along the class hierarchy. If the base
is virtual, it uses "vptr" in virtual class object, which indexes to
its derived class's vtable, to get and returns the baseclass offset.
If the base is non-virtual, it returns the accumulated offset of its
parent classes. The offset is then added to the address of the class
object to access its member in value_struct_elt_for_reference().

3 files changed, 166 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 9473646..d35abb5 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-10-08  Weimin Pan  <weimin.pan@oracle.com>
+
+	PR c++/16841
+	* gdb.cp/virtbase2.cc: New file.
+	* gdb.cp/virtbase2.exp: New file.
+
 2018-10-06  Tom Tromey  <tom@tromey.com>
 
 	PR python/19399:
diff --git a/gdb/testsuite/gdb.cp/virtbase2.cc b/gdb/testsuite/gdb.cp/virtbase2.cc
new file mode 100644
index 0000000..8b2fb77
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/virtbase2.cc
@@ -0,0 +1,49 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2018 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/>.  */
+
+struct super {
+  int w;
+  super () : w(17) {}
+};
+
+struct superbase {
+  int x;
+  superbase () : x(22) {}
+};
+
+struct base : superbase {
+  int i;
+  double d;
+  base() : i(55), d(6.25) {}
+};
+
+typedef base tbase;
+struct derived: virtual super, virtual tbase
+{
+  void func_d() { }
+};
+
+struct foo: virtual derived
+{
+  void func_f() { }
+};
+
+int main()
+{
+  derived().func_d();
+  foo().func_f();
+}
diff --git a/gdb/testsuite/gdb.cp/virtbase2.exp b/gdb/testsuite/gdb.cp/virtbase2.exp
new file mode 100644
index 0000000..cfb48cf
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/virtbase2.exp
@@ -0,0 +1,111 @@
+# Copyright 2018 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/>.
+
+# Make sure printing virtual base class data member works correctly (PR16841)
+
+if { [skip_cplus_tests] } { continue }
+
+standard_testfile .cc
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug c++}]} {
+    return -1
+}
+
+if {![runto_main]} then {
+    perror "couldn't run to main"
+    continue
+}
+
+# From a list of nested scopes, generate all possible ways of accessing something
+# in those scopes.  For example, with the argument {foo bar baz}, this proc will
+# return:
+#  - {} (empty string)
+#  - baz::
+#  - bar::
+#  - bar::baz::
+#  - foo::
+#  - foo::baz::
+#  - foo::bar::
+#  - foo::bar::baz::
+
+proc make_scope_list { scopes } {
+    if { [llength $scopes] == 1 } {
+        return [list "" "${scopes}::"]
+    }
+
+    # Pop the first element, save the first scope.
+    set this_scope [lindex $scopes 0]
+    set scopes [lreplace $scopes 0 0]
+
+    set child_result [make_scope_list $scopes]
+
+    # Add a copy of the child's result without this scope...
+    set result $child_result
+
+    # ... and a copy of the child's result with this scope.
+    foreach r $child_result {
+        lappend result "${this_scope}::$r"
+    }
+
+    return $result
+}
+
+proc test_variables_in_base { scopes } {
+    foreach scope [make_scope_list $scopes] {
+        gdb_test "print ${scope}i" " = 55"
+        gdb_test "print ${scope}d" " = 6.25"
+        gdb_test "print ${scope}x" " = 22"
+    }
+}
+
+proc test_variables_in_superbase { scopes } {
+    foreach scope [make_scope_list $scopes] {
+        gdb_test "print ${scope}x" " = 22"
+    }
+}
+
+proc test_variables_in_super { scopes } {
+    foreach scope [make_scope_list $scopes] {
+        gdb_test "print ${scope}w" " = 17"
+    }
+}
+
+with_test_prefix "derived::func_d" {
+    gdb_breakpoint "derived::func_d"
+    gdb_continue_to_breakpoint "continue to derived::func_d"
+    test_variables_in_base {derived base}
+    test_variables_in_superbase {derived base superbase}
+    test_variables_in_superbase {base superbase}
+    test_variables_in_superbase {derived superbase}
+    test_variables_in_superbase {superbase}
+    test_variables_in_superbase {base}
+    test_variables_in_super {super}
+    test_variables_in_super {derived super}
+}
+
+with_test_prefix "foo::func_f" {
+    gdb_breakpoint "foo::func_f"
+    gdb_continue_to_breakpoint "continue to foo::func_f"
+    test_variables_in_base {foo derived base}
+    test_variables_in_base {foo base}
+    test_variables_in_base {base}
+    test_variables_in_superbase {superbase}
+    test_variables_in_superbase {foo superbase}
+    test_variables_in_superbase {foo derived superbase}
+    test_variables_in_superbase {foo derived base superbase}
+    test_variables_in_super {super}
+    test_variables_in_super {foo super}
+    test_variables_in_super {foo derived super}
+}