[v2,PR,python/29603] Disable out-of-scope watchpoints
Commit Message
Currently, when a local software watchpoint goes out of scope, GDB sets the
watchpoint's disposition to `delete at next stop' and then normal stops
(i.e., stop and wait for the next GDB command). When GDB normal stops, it
automatically deletes the breakpoints with disposition set to
`delete at next stop'.
Suppose a Python script decides not to normal stop when a local software
watchpoint goes out of scope, the watchpoint will not be automatically
deleted even when its disposition is set to `delete at next stop'.
Since GDB single-steps the program and tests the watched expression after each
instruction, not deleting the watchpoint causes the watchpoint to be hit many
more times than it should, as reported in PR python/29603.
This was happening because the watchpoint is not disabled when going out of
scope.
This commit fixes this issue by disabling the watchpoint when going out of
scope. It also adds a test to ensure this feature isn't regressed in the
future.
There are two other solutions that seem to solve this issue but don't:
1. Automatically delete breakpoints on all kinds of stops
(in `fetch_inferior_event'). This solution is very slow since the deletion
requires O(N) time for N breakpoints.
2. Disable the watchpoint when the watchpoint's disposition is set to
`delete at next stop' (in `watchpoint_del_at_next_stop'). This solution
will not trigger a breakpoint stop callback when the watchpoint goes out of
scope.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29603
---
gdb/breakpoint.c | 2 +
gdb/testsuite/gdb.python/py-watchpoint.c | 27 ++++++++++++
gdb/testsuite/gdb.python/py-watchpoint.exp | 50 ++++++++++++++++++++++
gdb/testsuite/gdb.python/py-watchpoint.py | 30 +++++++++++++
4 files changed, 109 insertions(+)
create mode 100644 gdb/testsuite/gdb.python/py-watchpoint.c
create mode 100644 gdb/testsuite/gdb.python/py-watchpoint.exp
create mode 100644 gdb/testsuite/gdb.python/py-watchpoint.py
Comments
Hi,
I revised the patch after further investigation and
will send version 3 shortly.
Cheers,
Johnson
@@ -5340,6 +5340,8 @@ bpstat_check_breakpoint_conditions (bpstat *bs, thread_info *thread)
/* Evaluate extension language breakpoints that have a "stop" method
implemented. */
bs->stop = breakpoint_ext_lang_cond_says_stop (b);
+ if (b->disposition == disp_del_at_next_stop)
+ disable_breakpoint(b);
if (is_watchpoint (b))
{
new file mode 100644
@@ -0,0 +1,27 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2022 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/>. */
+
+#include <stdio.h>
+
+int
+main ()
+{
+ int i;
+ for (i = 0; i < 3; i++)
+ printf ("%d", i);
+ return 0;
+}
new file mode 100644
@@ -0,0 +1,50 @@
+# Copyright (C) 2022 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/>.
+
+# This file is part of the GDB testsuite. It checks Watchpoints
+# are deleted after used.
+
+load_lib gdb-python.exp
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile]} {
+ return -1
+}
+
+# Skip all tests if Python scripting is not enabled.
+if { [skip_python_tests] } { continue }
+
+if ![runto_main] then {
+ return 0
+}
+
+#
+# Check Watchpoints are deleted after used
+#
+
+gdb_test_no_output "set can-use-hw-watchpoints 0" "Don't use hardware watchpoints"
+gdb_test "python print(len(gdb.breakpoints()))" "1" "check default BP count"
+gdb_test "source ${srcdir}/${subdir}/${testfile}.py" ".*Python script imported.*" \
+ "import python scripts"
+gdb_test "python print(len(gdb.breakpoints()))" "2" "check modified BP count"
+gdb_test_sequence "continue" "run until program stops" {
+ "Watchpoint Hit: ."
+ "\[\r\n\]+Watchpoint . deleted because the program has left the block in"
+ "\[\r\n\]+which its expression is valid\."
+ "Watchpoint Hit: ."
+ "\[\r\n\]+012\\[Inferior 1 \\(process .*\\) exited normally\\]"
+}
+gdb_test "python print(len(gdb.breakpoints()))" "1" "check BP count"
new file mode 100644
@@ -0,0 +1,30 @@
+# Copyright (C) 2022 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/>.
+
+# This file is part of the GDB testsuite. It checks Watchpoints
+# are deleted after used.
+
+class MyBreakpoint(gdb.Breakpoint):
+ def __init__(self, *args, **kwargs):
+ gdb.Breakpoint.__init__(self, *args, **kwargs)
+ self.i = 0
+ def stop(self):
+ self.i += 1
+ print("Watchpoint Hit:", self.i)
+ return False
+
+MyBreakpoint('i', gdb.BP_WATCHPOINT)
+
+print("Python script imported")