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[PATCH] Fix watching structs in C++
- From: Andreas Arnez <arnez at linux dot vnet dot ibm dot com>
- To: gdb-patches at sourceware dot org
- Date: Tue, 27 Feb 2018 19:07:23 +0100
- Subject: [PATCH] Fix watching structs in C++
- Authentication-results: sourceware.org; auth=none
Some of the watchpoint logic depends on the fact that the head of the
value chain represents the user-specified value to watch. Thus no
additional values should be added to the value chain after that. However,
this may happen in gnuv3_rrti_type, where value_addr is invoked. If no
RTTI is found, then the pointer value built by value_addr, rather than the
original value, stays in front of the value chain.
With such a "polluted" value chain the watchpoint logic does not recognize
when the user intended to watch a struct, and can_use_hardware_watchpoint
returns zero. Instead of a hardware watchpoint, a software watchpoint
will then be set for no apparent reason.
This is fixed by adding an early exit to gnuv3_rtti_type when the input
value is not a dynamic class object.
gdb/testsuite/ChangeLog:
* gdb.cp/watch-cp.cc: New test.
* gdb.cp/watch-cp.exp: New file.
gdb/ChangeLog:
* gnu-v3-abi.c (gnuv3_rtti_type): Add early exit if the given
value is not a dynamic class object.
---
gdb/gnu-v3-abi.c | 5 +++--
gdb/testsuite/gdb.cp/watch-cp.cc | 28 ++++++++++++++++++++++++++++
gdb/testsuite/gdb.cp/watch-cp.exp | 35 +++++++++++++++++++++++++++++++++++
3 files changed, 66 insertions(+), 2 deletions(-)
create mode 100644 gdb/testsuite/gdb.cp/watch-cp.cc
create mode 100644 gdb/testsuite/gdb.cp/watch-cp.exp
diff --git a/gdb/gnu-v3-abi.c b/gdb/gnu-v3-abi.c
index 0965846ce6..859187f2e9 100644
--- a/gdb/gnu-v3-abi.c
+++ b/gdb/gnu-v3-abi.c
@@ -299,8 +299,9 @@ gnuv3_rtti_type (struct value *value,
LONGEST offset_to_top;
const char *atsign;
- /* We only have RTTI for class objects. */
- if (TYPE_CODE (values_type) != TYPE_CODE_STRUCT)
+ /* We only have RTTI for dynamic class objects. */
+ if (TYPE_CODE (values_type) != TYPE_CODE_STRUCT
+ || !gnuv3_dynamic_class (values_type))
return NULL;
/* Determine architecture. */
diff --git a/gdb/testsuite/gdb.cp/watch-cp.cc b/gdb/testsuite/gdb.cp/watch-cp.cc
new file mode 100644
index 0000000000..6954e854c9
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/watch-cp.cc
@@ -0,0 +1,28 @@
+/* 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/>. */
+
+/* A class that does not have RTTI and is small enough to fit in a
+ hardware watchpoint on all targets. */
+class smallstuff { public: int n; };
+
+smallstuff watchme[5];
+
+int
+main ()
+{
+ for (int i = 0; i < sizeof (watchme) / sizeof (watchme[0]); i++)
+ watchme[i].n = i;
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.cp/watch-cp.exp b/gdb/testsuite/gdb.cp/watch-cp.exp
new file mode 100644
index 0000000000..bdf0f13886
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/watch-cp.exp
@@ -0,0 +1,35 @@
+# 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/>.
+
+if { [skip_cplus_tests] || [skip_hw_watchpoint_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_test "watch watchme\[3\]" "atchpoint .*: watchme.*" "set watchpoint"
+
+# Verify that a hardware watchpoint is used.
+gdb_test "info watchpoints" " hw watchpoint .* watchme.*"
+
+# Now see whether it actually works.
+gdb_test "continue" "Hardware watchpoint .*New value = \\{n = 3\\}.*"
--
2.14.3