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. A 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, we need to use "vptr" in the virtual class object,
which indexes to its derived class's vtable, to fetch the virtual base
offset. The offset is then added to the virtual class object to access
its member in value_struct_elt_for_reference().
The new function add_virtual_base_offset searches recursively for the
base class along the class hierarchy and returns the virtual base offset
for the virtual class.
Tested on amd64-linux-gnu. No regressions.
---
gdb/ChangeLog | 7 +++++
gdb/testsuite/ChangeLog | 6 ++++
gdb/testsuite/gdb.cp/virtbase2.cc | 21 +++++++++++++++
gdb/testsuite/gdb.cp/virtbase2.exp | 50 ++++++++++++++++++++++++++++++++++++
gdb/valops.c | 38 +++++++++++++++++++++++++++
5 files changed, 122 insertions(+), 0 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..9d86f1c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2018-08-23 Weimin Pan <weimin.pan@oracle.com>
+
+ PR gdb/16841
+ * valops.c (add_virtual_base_offset): New function.
+ (value_struct_elt_for_reference): Use it to get virtual base offset
+ and add it in calculating class member address.
+
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..7be2e1d 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-08-23 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..4f7631e
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/virtbase2.cc
@@ -0,0 +1,21 @@
+struct base {
+ int i; double d;
+ base() : i(55), d(6.6) {}
+};
+typedef base tbase;
+struct derived: 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..c29ff1c
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/virtbase2.exp
@@ -0,0 +1,50 @@
+# 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_d"
+gdb_continue_to_breakpoint "continue to derived::func_d"
+gdb_test "print i" " = 55" "i in base class"
+gdb_test "print derived::i" " = 55" "i in base class"
+gdb_test "print derived::base::i" " = 55" "i in base class"
+gdb_test "print base::i" " = 55" "i in base class"
+gdb_test "print d" " = 6.5999999999999996" "d in base class"
+gdb_test "print derived::d" " = 6.5999999999999996" "d in base class"
+gdb_test "print derived::base::d" " = 6.5999999999999996" "d in base class"
+gdb_test "print base::d" " = 6.5999999999999996" "d in base class"
+gdb_breakpoint "foo::func_f"
+gdb_continue_to_breakpoint "continue to foo::func_f"
+gdb_test "print i" " = 55" "i in base class"
+gdb_test "print derived::i" " = 55" "i in base class"
+gdb_test "print derived::base::i" " = 55" "i in base class"
+gdb_test "print base::i" " = 55" "i in base class"
+gdb_test "print d" " = 6.5999999999999996" "d in base class"
+gdb_test "print derived::d" " = 6.5999999999999996" "d in base class"
+gdb_test "print derived::base::d" " = 6.5999999999999996" "d in base class"
+gdb_test "print base::d" " = 6.5999999999999996" "d in base class"
diff --git a/gdb/valops.c b/gdb/valops.c
index 9bdbf22..754e7d0 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -3329,6 +3329,35 @@ compare_parameters (struct type *t1, struct type *t2, int skip_artificial)
return 0;
}
+/* C++: Given an aggregate type VT, and a class type CLS,
+ search recursively for CLS and return its offset,
+ relative to VT, if it is a virtual base member. */
+
+static int
+add_virtual_base_offset (struct type *vt, struct type *cls,
+ struct value *v, int &boffs)
+{
+ for (int i = 0; i < TYPE_N_BASECLASSES (vt); i++)
+ {
+ struct type *ftype = TYPE_FIELD_TYPE (vt, i);
+ if (check_typedef (ftype) == cls)
+ {
+ if (BASETYPE_VIA_VIRTUAL (vt, i))
+ {
+ const gdb_byte *adr = value_contents_for_printing (v);
+ boffs = baseclass_offset (vt, i, adr, value_offset (v),
+ value_as_long (v), v);
+ }
+ return true;
+ }
+
+ if (add_virtual_base_offset (ftype, cls, v, boffs))
+ return true;
+ }
+
+ return false;
+}
+
/* C++: Given an aggregate type CURTYPE, and a member name NAME,
return the address of this member as a "pointer to member" type.
If INTYPE is non-null, then it will be the type of the member we
@@ -3393,6 +3422,15 @@ value_struct_elt_for_reference (struct type *domain, int offset,
tmp = lookup_pointer_type (TYPE_SELF_TYPE (type));
v = value_cast_pointers (tmp, v, 1);
mem_offset = value_as_long (ptr);
+ if (domain != curtype)
+ {
+ struct value *v2 = value_of_this_silent (current_language);
+ struct type *vtype = check_typedef (value_type (v2));
+ struct type *vt = check_typedef (TYPE_TARGET_TYPE (vtype));
+ int base_offs = 0;
+ if (add_virtual_base_offset (vt, curtype, v, base_offs))
+ mem_offset += base_offs;
+ }
tmp = lookup_pointer_type (TYPE_TARGET_TYPE (type));
result = value_from_pointer (tmp,
value_as_long (v) + mem_offset);