[PATCH PR gdb/16841] virtual inheritance via typedef cannot find base

[Weimin Pan <weimin.pan@oracle.com>]

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
$2 = 0
(gdb) p derived::base::i
$3 = 0
(gdb) p derived::i
$4 = 4196392

To fix the problem, the virtual-base offset, relative to its derived class,
needs to be fetched, via baseclass_offset(), and used in calculating the
address of its data member in value_struct_elt_for_reference().

Tested on amd64-linux-gnu. No regressions.
---
 gdb/ChangeLog                      |    6 +++++
 gdb/testsuite/ChangeLog            |    6 +++++
 gdb/testsuite/gdb.cp/virtbase2.cc  |   28 ++++++++++++++++++++++++++
 gdb/testsuite/gdb.cp/virtbase2.exp |   38 ++++++++++++++++++++++++++++++++++++
 gdb/valops.c                       |   17 +++++++++++++++-
 5 files changed, 94 insertions(+), 1 deletions(-)
 create mode 100644 gdb/testsuite/gdb.cp/virtbase2.cc
 create mode 100644 gdb/testsuite/gdb.cp/virtbase2.exp

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index c47c111..1531ff1 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2018-07-20  Weimin Pan  <weimin.pan@oracle.com>
+
+	PR gdb/16841
+	* valops.c (value_struct_elt_for_reference): Calculate virtual
+	baseclass offset, relative to its derived class.
+
 2018-06-29  Pedro Alves  <palves@redhat.com>
 
 	* gdb/amd64-tdep.h (amd64_create_target_description): Add
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 93c849c..1577a54 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-07-20  Weimin Pan  <weimin.pan@oracle.com>
+
+	PR gdb/16841
+	* gdb.cp/virtbase2.cc: New file.
+	* gdb.cp/virtbase2.exp: New file.
+
 2018-06-29  Pedro Alves  <palves@redhat.com>
 
 	* gdb.threads/names.exp: Adjust expected "info threads" output.
diff --git a/gdb/testsuite/gdb.cp/virtbase2.cc b/gdb/testsuite/gdb.cp/virtbase2.cc
new file mode 100644
index 0000000..33753b3
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/virtbase2.cc
@@ -0,0 +1,28 @@
+/* This test script 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 left { int i; };
+struct right {int j;};
+struct derived: virtual left, virtual right
+{
+  void func() { }
+};
+
+int main()
+{
+  derived().func();
+}
diff --git a/gdb/testsuite/gdb.cp/virtbase2.exp b/gdb/testsuite/gdb.cp/virtbase2.exp
new file mode 100644
index 0000000..01dd298
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/virtbase2.exp
@@ -0,0 +1,38 @@
+# 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 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
+}
+
+gdb_breakpoint "derived::func"
+gdb_continue_to_breakpoint "continue to derived::func"
+gdb_test "print j" " = 0" "j in base class right"
+gdb_test "print i" " = 0" "i in base class left"
+gdb_test "print derived::j" " = 0" "j in base class right"
+gdb_test "print derived::i" " = 0" "i in base class left"
+gdb_test "print derived::right::j" " = 0" "j in base class right"
+gdb_test "print derived::left::i" " = 0" "i in base class left"
diff --git a/gdb/valops.c b/gdb/valops.c
index 9bdbf22..f0a8118 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -3385,6 +3385,7 @@ value_struct_elt_for_reference (struct type *domain, int offset,
 		  struct value *ptr;
 		  long mem_offset;
 		  struct type *type, *tmp;
+		  int index;
 
 		  ptr = value_aggregate_elt (domain, name, NULL, 1, noside);
 		  type = check_typedef (value_type (ptr));
@@ -3392,7 +3393,21 @@ value_struct_elt_for_reference (struct type *domain, int offset,
 			      && TYPE_CODE (type) == TYPE_CODE_MEMBERPTR);
 		  tmp = lookup_pointer_type (TYPE_SELF_TYPE (type));
 		  v = value_cast_pointers (tmp, v, 1);
-		  mem_offset = value_as_long (ptr);
+		  for (index = 0; index < TYPE_NFIELDS (domain); index++) 
+		    { 
+		      if (TYPE_FIELDS (domain)[index].type == curtype) 
+		        break; 
+		    } 
+		  if (index != TYPE_NFIELDS (domain) 
+		      && BASETYPE_VIA_VIRTUAL (domain, index)) 
+		    { 
+		      const gdb_byte *adr = value_contents_for_printing (ptr); 
+		      mem_offset = baseclass_offset (domain, index, adr, 
+						     value_offset (ptr), 
+						     value_as_long (v), ptr); 
+		    } 
+		  else 
+		      mem_offset = value_as_long (ptr);
 		  tmp = lookup_pointer_type (TYPE_TARGET_TYPE (type));
 		  result = value_from_pointer (tmp,
 					       value_as_long (v) + mem_offset);
-- 
1.7.1