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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().
This commit is contained in:
Weimin Pan 2018-10-08 21:16:59 +00:00
parent 780f601cf3
commit 9f6b697b0e
5 changed files with 235 additions and 1 deletions
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7
gdb/ChangeLog
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@ -1,3 +1,10 @@
2018-10-08 Weimin Pan <weimin.pan@oracle.com>
PR c++/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.
2018-10-08 John Darrington <john@darrington.wattle.id.au>
* dwarf2read.c (dwarf2_cu) <producer_is_codewarrior>: New field.

6
gdb/testsuite/ChangeLog
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@ -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:

49
gdb/testsuite/gdb.cp/virtbase2.cc Normal file
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@ -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();
}

111
gdb/testsuite/gdb.cp/virtbase2.exp Normal file
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@ -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}
}

63
gdb/valops.c
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@ -3321,6 +3321,49 @@ 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
@ -3374,7 +3417,7 @@ value_struct_elt_for_reference (struct type *domain, int offset,
struct value *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;
@ -3385,6 +3428,24 @@ 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);