[PATCHv6 07/10] gdb: don't set breakpoint::pspace for in create_breakpoint

Andrew Burgess
2023-12-02T10:43:23Z

While working on the previous commit, I ran into this code within
create_breakpoint:

if ((type_wanted != bp_breakpoint
&& type_wanted != bp_hardware_breakpoint) || thread != -1)
b->pspace = current_program_space;

this code is only executed when creating a pending breakpoint, and
sets the breakpoint::pspace member variable.

The above code gained the 'thread != -1' clause with this commit:

commit cc72b2a2da6d6372cbdb1d14639a5fce84e1a325
Date: Fri Dec 23 17:06:16 2011 +0000

Introduce gdb.FinishBreakpoint in Python

While the type_wanted checks were added with this commit:

commit f8eba3c61629b3c03ac1f33853eab4d8507adb9c
Date: Tue Dec 6 18:54:43 2011 +0000

the "ambiguous linespec" series

Before this breakpoint::pspace was set unconditionally.

If we look at how breakpoint::pspace is used today, some breakpoint
types specifically set this field, either in their constructors, or in
a wrapper function that calls the constructor. So, the watchpoint
type and its sub-class set this variable, as does the catchpoint type,
and all it's sub-classes.

However, code_breakpoint doesn't specifically set this field within
its constructor, though some sub-classes of
code_breakpoint (ada_catchpoint, exception_catchpoint,
internal_breakpoint, and momentary_breakpoint) do set this field.

When I examine all the places that breakpoint::pspace is used, I
believe that in every place where it is expected that this field is
set, the breakpoint type will be one that specifically sets this
field.

Next, I observe two problems with the existing code.

First, the above code is only hit for pending breakpoints, there's no
equivalent code for non-pending breakpoints. This opens up the
possibility of GDB entering non-consistent states; if a breakpoint is
first created pending and then later gets a location, the pspace field
will be set, while if the breakpoint is immediately non-pending, then
the pspace field will never be set.

Second, if we look at how breakpoint::pspace is used in the function
breakpoint_program_space_exit, we see that when a program space is
removed, any breakpoint with breakpoint::pspace set to the removed
program space, will be deleted. This makes sense, but does mean we
need to ensure breakpoint::pspace is only set for breakpoints that
apply to a single program space.

So, if I create pending dprintf breakpoint (type bp_dprintf) then the
breakpoint::pspace variable will be set even though the dprintf is not
really tied to that one program space. As a result, when the matching
program space is removed the dprintf is incorrectly removed.

Also, if I create a thread specific breakpoint, then, thanks to the
'thread != -1' clause the wrong program space will be stored in
breakpoint::pspace (the current program space is always used, which
might not be the program space that corresponds to the selected
thread), as a result, the thread specific breakpoint will be deleted
when the matching program space is removed.

If we look at commit cc72b2a2da6d which added the 'thread != -1'
clause, we can see this change was entirely redundant, the
breakpoint::pspace is also set in bpfinishpy_init after
create_breakpoint has been called. As such, I think we can safely
drop the 'thread != -1' clause.

For the other problems, I'm proposing to be pretty aggressive - I'd
like to drop the breakpoint::pspace assignment completely from
create_breakpoint. Having looked at how this variable is used, I
believe that it is already set elsewhere in all the cases that it is
needed. Maybe this code was needed at one time, but I can't see how
it's needed any more.

There's tests to expose the issues I've spotted with this code, and
there's no regressions in testing.
---
gdb/breakpoint.c | 3 -
gdb/breakpoint.h | 18 +-
.../gdb.multi/pending-bp-del-inferior.c | 28 +++
.../gdb.multi/pending-bp-del-inferior.exp | 216 ++++++++++++++++++
4 files changed, 259 insertions(+), 6 deletions(-)
create mode 100644 gdb/testsuite/gdb.multi/pending-bp-del-inferior.c
create mode 100644 gdb/testsuite/gdb.multi/pending-bp-del-inferior.exp

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index e2cd4d360f2..bbf28d82558 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -9207,9 +9207,6 @@ create_breakpoint (struct gdbarch *gdbarch,
b->disposition = tempflag ? disp_del : disp_donttouch;
b->condition_not_parsed = 1;
b->enable_state = enabled ? bp_enabled : bp_disabled;
- if ((type_wanted != bp_breakpoint
- && type_wanted != bp_hardware_breakpoint) || thread != -1)
- b->pspace = current_program_space;

if (b->type == bp_dprintf)
update_dprintf_command_list (b.get ());
diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
index 95f98b59e41..2bf63b90072 100644
--- a/gdb/breakpoint.h
+++ b/gdb/breakpoint.h
@@ -823,9 +823,21 @@ struct breakpoint : public intrusive_list_node<breakpoint>
equals this. */
struct frame_id frame_id = null_frame_id;

- /* The program space used to set the breakpoint. This is only set
- for breakpoints which are specific to a program space; for
- non-thread-specific ordinary breakpoints this is NULL. */
+ /* The program space used to set the breakpoint. This is only set for
+ breakpoints that are not type bp_breakpoint or bp_hardware_breakpoint.
+ For thread or inferior specific breakpoints, the breakpoints are
+ managed via the thread and inferior member variables. */
+
+ /* If not nullptr then this is the program space for which this
+ breakpoint was created. All watchpoint and catchpoint sub-types set
+ this field, but not all of the code_breakpoint sub-types do;
+ generally, user created breakpoint types don't set this field, though
+ things might be more consistent if they did.
+
+ When this variable is nullptr then a breakpoint might be associated
+ with multiple program spaces, though you need to check the thread,
+ inferior and task variables to see if a breakpoint was created for a
+ specific thread, inferior, or Ada task respectively. */
program_space *pspace = NULL;

/* The location specification we used to set the breakpoint. */
diff --git a/gdb/testsuite/gdb.multi/pending-bp-del-inferior.c b/gdb/testsuite/gdb.multi/pending-bp-del-inferior.c
new file mode 100644
index 00000000000..51b6492085f
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/pending-bp-del-inferior.c
@@ -0,0 +1,28 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2023 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/>. */
+
+int
+foo ()
+{
+ return 0;
+}
+
+int
+main ()
+{
+ return foo ();
+}
diff --git a/gdb/testsuite/gdb.multi/pending-bp-del-inferior.exp b/gdb/testsuite/gdb.multi/pending-bp-del-inferior.exp
new file mode 100644
index 00000000000..cb1f119ff94
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/pending-bp-del-inferior.exp
@@ -0,0 +1,216 @@
+# Copyright 2023 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/>.
+
+# Setup two inferiors. Select one inferior and create a pending
+# thread specific breakpoint in the other inferior.
+#
+# Delete the selected inferior (the one for which the thread specific
+# breakpoint doesn't apply), and check that the breakpoint still exists.
+#
+# Repeat this process, but this time, create an inferior specific
+# breakpoint.
+
+# The plain remote target can't do multiple inferiors.
+require !use_gdb_stub
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile]} {
+ return -1
+}
+
+# Setup for the tests. Create two inferiors, both running the global
+# BINFILE, and proceed to main in both inferiors. Delete all
+# breakpoints, and check that we do have two threads.
+#
+# Return true after a successful setup, otherwise, return false.
+proc test_setup {} {
+ clean_restart $::binfile
+
+ if {![runto_main]} {
+ return 0
+ }
+
+ gdb_test "add-inferior -exec ${::binfile}" "Added inferior 2.*" \
+ "add inferior 2"
+ gdb_test "inferior 2" "Switching to inferior 2 .*" \
+ "select inferior 2"
+
+ if {![runto_main]} {
+ return 0
+ }
+
+ delete_breakpoints
+
+ gdb_test "info threads" \
+ [multi_line \
+ " Id\\s+Target Id\\s+Frame\\s*" \
+ " 1\\.1\\s+\[^\r\n\]+" \
+ "\\* 2\\.1\\s+\[^\r\n\]+"] \
+ "check we have the expected threads"
+
+ return 1
+}
+
+# Assuming inferior 2 is already selected, kill the current inferior
+# (inferior 2), selected inferior 1, and then remove inferior 2.
+proc kill_and_remove_inferior_2 {} {
+ gdb_test "kill" "" "kill inferior 2" \
+ "Kill the program being debugged.*y or n. $" "y"
+
+ gdb_test "inferior 1" "Switching to inferior 1 .*" \
+ "select inferior 1"
+
+ gdb_test_no_output "remove-inferiors 2"
+}
+
+# Setup two inferiors, then created a breakpoint. If BP_PENDING is
+# true then the breakpoint will be pending, otherwise, the breakpoint
+# will be non-pending.
+#
+# BP_TYPE is either 'thread' or 'inferior', and indicates if the
+# created breakpoint should be thread or inferior specific.
+#
+# The breakpoint is created while inferior 2 is selected, and the
+# thread/inferior restriction always identifies inferior 1.
+#
+# Then inferior 2 is killed and removed.
+#
+# Finally, check that the breakpoint still exists and correctly refers
+# to inferior 1.
+proc do_bp_test { bp_type bp_pending } {
+ if {![test_setup]} {
+ return
+ }
+
+ if { $bp_pending } {
+ set bp_func "bar"
+ } else {
+ set bp_func "foo"
+ }
+
+ if { $bp_type eq "thread" } {
+ set bp_restriction "thread 1.1"
+ } else {
+ set bp_restriction "inferior 1"
+ }
+
+ gdb_breakpoint "$bp_func $bp_restriction" allow-pending
+ set bp_number [get_integer_valueof "\$bpnum" "INVALID" \
+ "get b/p number for previous breakpoint"]
+
+ if { $bp_restriction eq "thread 1.1" } {
+ set bp_after_restriction "thread 1"
+ } else {
+ set bp_after_restriction $bp_restriction
+ }
+
+ if { $bp_pending } {
+ set bp_pattern_before \
+ [multi_line \
+ "$bp_number\\s+breakpoint\\s+keep\\s+y\\s+<PENDING>\\s+${bp_func}" \
+ "\\s+stop only in [string_to_regexp $bp_restriction]"]
+ set bp_pattern_after \
+ [multi_line \
+ "$bp_number\\s+breakpoint\\s+keep\\s+y\\s+<PENDING>\\s+${bp_func}" \
+ "\\s+stop only in [string_to_regexp $bp_after_restriction]"]
+ } else {
+ set bp_pattern_before \
+ [multi_line \
+ "$bp_number\\s+breakpoint\\s+keep\\s+y\\s+<MULTIPLE>\\s*" \
+ "\\s+stop only in [string_to_regexp $bp_restriction]" \
+ "$bp_number\\.1\\s+y\\s+$::hex in $bp_func at \[^\r\n\]+ inf 1" \
+ "$bp_number\\.2\\s+y\\s+$::hex in $bp_func at \[^\r\n\]+ inf 2"]
+
+ set bp_pattern_after \
+ [multi_line \
+ "$bp_number\\s+breakpoint\\s+keep\\s+y\\s+$::hex in $bp_func at \[^\r\n\]+" \
+ "\\s+stop only in [string_to_regexp $bp_after_restriction]"]
+ }
+
+ gdb_test "info breakpoints" $bp_pattern_before \
+ "info breakpoints before inferior removal"
+
+ kill_and_remove_inferior_2
+
+ gdb_test "info breakpoints" $bp_pattern_after \
+ "info breakpoints after inferior removal"
+}
+
+# Setup two inferiors, then created a dprintf. If BP_PENDING is
+# true then the dprintf will be pending, otherwise, the dprintf
+# will be non-pending.
+#
+# The dprintf is created while inferior 2. Then inferior 2 is killed
+# and removed.
+#
+# Finally, check that the dprintf still exists.
+proc do_dprintf_test { bp_pending } {
+ if {![test_setup]} {
+ return
+ }
+
+ if { $bp_pending } {
+ set bp_func "bar"
+
+ gdb_test "dprintf $bp_func,\"in $bp_func\"" ".*" \
+ "create dprintf breakpoint" \
+ "Make dprintf pending on future shared library load\\? \\(y or .n.\\) $" "y"
+ } else {
+ set bp_func "foo"
+
+ gdb_test "dprintf $bp_func,\"in $bp_func\"" ".*" \
+ "create dprintf breakpoint"
+ }
+
+ set bp_number [get_integer_valueof "\$bpnum" "INVALID" \
+ "get b/p number for previous breakpoint"]
+
+ if { $bp_pending } {
+ set bp_pattern_before \
+ [multi_line \
+ "$bp_number\\s+dprintf\\s+keep\\s+y\\s+<PENDING>\\s+${bp_func}" \
+ "\\s+printf \"in $bp_func\""]
+ set bp_pattern_after $bp_pattern_before
+ } else {
+ set bp_pattern_before \
+ [multi_line \
+ "$bp_number\\s+dprintf\\s+keep\\s+y\\s+<MULTIPLE>\\s*" \
+ "\\s+printf \"in $bp_func\"" \
+ "$bp_number\\.1\\s+y\\s+$::hex in $bp_func at \[^\r\n\]+ inf 1" \
+ "$bp_number\\.2\\s+y\\s+$::hex in $bp_func at \[^\r\n\]+ inf 2"]
+
+ set bp_pattern_after \
+ [multi_line \
+ "$bp_number\\s+dprintf\\s+keep\\s+y\\s+$::hex in $bp_func at \[^\r\n\]+" \
+ "\\s+printf \"in $bp_func\""]
+ }
+
+ gdb_test "info breakpoints" $bp_pattern_before \
+ "info breakpoints before inferior removal"
+
+ kill_and_remove_inferior_2
+
+ gdb_test "info breakpoints" $bp_pattern_after \
+ "info breakpoints after inferior removal"
+}
+
+foreach_with_prefix bp_pending { true false } {
+ foreach_with_prefix bp_type { thread inferior } {
+ do_bp_test $bp_type $bp_pending
+ }
+
+ do_dprintf_test $bp_pending
+}
--
2.25.4