[PATCH v3 PR gdb/16841] virtual inheritance via typedef cannot find base
Weimin Pan
weimin.pan@oracle.com
Thu Sep 13 01:39:00 GMT 2018
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, 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().
Tested on amd64-linux-gnu. No regressions.
---
gdb/ChangeLog | 7 +++
gdb/testsuite/ChangeLog | 6 +++
gdb/testsuite/gdb.cp/virtbase2.cc | 46 +++++++++++++++++++++
gdb/testsuite/gdb.cp/virtbase2.exp | 78 ++++++++++++++++++++++++++++++++++++
gdb/valops.c | 63 ++++++++++++++++++++++++++++-
5 files changed, 199 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..9cbd8ca 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2018-09-12 Weimin Pan <weimin.pan@oracle.com>
+
+ PR gdb/16841
+ * valops.c (get_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..46f16d7 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-09-12 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..60c95c4
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/virtbase2.cc
@@ -0,0 +1,46 @@
+/* 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 superbase {
+ int x;
+ superbase () : x(22) {}
+};
+
+struct base : superbase {
+ 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..4c14419
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/virtbase2.exp
@@ -0,0 +1,78 @@
+# 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
+}
+
+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" " = 6.5999999999999996"
+ }
+}
+
+proc test_variables_in_superbase { scopes } {
+ foreach scope [make_scope_list $scopes] {
+ gdb_test "print ${scope}x" " = 22"
+ }
+}
+
+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}
+}
+
+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_superbase {foo derived base superbase}
+}
diff --git a/gdb/valops.c b/gdb/valops.c
index 9bdbf22..ce39330 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -3329,6 +3329,49 @@ 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 using value V; If found, store the offset
+ which is either fetched from the virtual base pointer if CLS
+ is virtual or accumulated offset of its parent classes if
+ CLS is non-virtual in *BOFFS, set ISVIRT to indicate if CLS
+ is virtual, and return true. If not found, return false. */
+
+static bool
+get_baseclass_offset (struct type *vt, struct type *cls,
+ struct value *v, int *boffs, bool *isvirt)
+{
+ for (int i = 0; i < TYPE_N_BASECLASSES (vt); i++)
+ {
+ struct type *t = TYPE_FIELD_TYPE (vt, i);
+ if (types_equal (t, 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);
+ *isvirt = true;
+ }
+ else
+ *isvirt = false;
+ return true;
+ }
+
+ if (get_baseclass_offset (check_typedef (t), cls, v, boffs, isvirt))
+ {
+ if (*isvirt == false) /* Add non-virtual base offset. */
+ {
+ 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;
+ }
+ }
+
+ 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
@@ -3382,7 +3425,7 @@ value_struct_elt_for_reference (struct type *domain, int offset,
v = value_of_this_silent (current_language);
if (v != NULL)
{
- struct value *ptr;
+ struct value *ptr, *this_v = v;
long mem_offset;
struct type *type, *tmp;
@@ -3393,6 +3436,24 @@ 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)
+ {
+ /* Find class offset of type CURTYPE from either its
+ parent type DOMAIN or the type of implied this. */
+ int boff = 0;
+ bool isvirt = false;
+ if (get_baseclass_offset (domain, curtype, v, &boff,
+ &isvirt))
+ mem_offset += boff;
+ else
+ {
+ struct type *t = check_typedef (value_type (this_v));
+ t = check_typedef (TYPE_TARGET_TYPE (t));
+ if (get_baseclass_offset (t, curtype, this_v,
+ &boff, &isvirt))
+ mem_offset += boff;
+ }
+ }
tmp = lookup_pointer_type (TYPE_TARGET_TYPE (type));
result = value_from_pointer (tmp,
value_as_long (v) + mem_offset);
--
1.7.1
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