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Re: Don't delete local watchpoints just because a different thread stopped.
On Thursday 19 November 2009 17:45:39, Daniel Jacobowitz wrote:
> On Thu, Nov 19, 2009 at 02:07:01AM +0000, Pedro Alves wrote:
> > One could even come up with a test case where the current
> > frame id on this other thread does happen to be in the
> > frame chain. Shouldn't be hard to trigger if the threads
> > are running the same function --- GDB can then mistakenly
> > try to extract a new current watchpoint value on the wrong
> > thread context.
>
> I hope your threads have different stacks :-) So I don't think this
> case happens.
Urgh, talk about braino! :-P :-)
>
> > Index: src/gdb/breakpoint.h
> > ===================================================================
> > --- src.orig/gdb/breakpoint.h 2009-11-19 01:10:05.000000000 +0000
> > +++ src/gdb/breakpoint.h 2009-11-19 01:10:16.000000000 +0000
> > @@ -457,6 +457,10 @@ struct breakpoint
> > should be evaluated on the outermost frame. */
> > struct frame_id watchpoint_frame;
> >
> > + /* Holds the thread which identifies the frame this watchpoint
> > + should be considered in scope for, or -1 if don't care. */
> > + int watchpoint_thread;
> > +
> > /* For hardware watchpoints, the triggered status according to the
> > hardware. */
> > enum watchpoint_triggered watchpoint_triggered;
>
> Why not just use a ptid? If the answer has to do with ptid reuse,
> then we ought to delete the watchpoint before that comes up - anyway,
> at least deserves a comment of what units this is in.
No reason. I started out with a hack using the bkpt->thread field, then
decided to keep user visible things distinct from internal things, and
just copy/pasted the field --- the int'ness sticked. Indeed a ptid
makes things simpler. Thanks.
> > @@ -1004,6 +1028,12 @@ update_watchpoint (struct breakpoint *b,
> > bpstat bs;
> > struct program_space *frame_pspace;
> >
> > + /* If this is a local watchpoint, we only want to check if the
> > + watchpoint frame is in scope if the current thread is the thread
> > + that was used to create the watchpoint. */
> > + if (!watchpoint_thread_match (b))
> > + return;
> > +
> > /* We don't free locations. They are stored in bp_location array and
> > update_global_locations will eventually delete them and remove
> > breakpoints if needed. */
>
> For all-stop, do we want to check whenever the watchpoint's thread is
> stopped?
Yep (non-stop), good catch. Usually we'd get here with a stopped
thread, but there's always say,
'(gdb) file' -> breakpoint_re_set -> update_watchpoint.
I'm actually thinking that path may need further
tweaking if the current thread is running, but I'll defer
putting more brain cycles on that until more non-stop watchpoint
support is in place.
Here's the updated patch. New test unchanged. Tested on x86_64-linux.
2009-11-19 Pedro Alves <pedro@codesourcery.com>
gdb/
* breakpoint.h (struct breakpoint) <watchpoint_thread>: New field.
* breakpoint.c (watchpoint_in_thread_scope): New.
(update_watchpoint): Skip if the local watchpoint's thread doesn't
match the current thread, or if the current thread is running.
(watchpoint_check): Ditto.
(watch_command_1): Set the watchpoint's watchpoint_thread field.
2009-11-19 Pedro Alves <pedro@codesourcery.com>
gdb/testsuite/
* local-watch-wrong-thread.c, local-watch-wrong-thread.exp: New
files.
More comments?
--
Pedro Alves
2009-11-19 Pedro Alves <pedro@codesourcery.com>
gdb/
* breakpoint.h (struct breakpoint) <watchpoint_thread>: New field.
* breakpoint.c (watchpoint_in_thread_scope): New.
(update_watchpoint): Skip if the local watchpoint's thread doesn't
match the current thread, or if the current thread is running.
(watchpoint_check): Ditto.
(watch_command_1): Set the watchpoint's watchpoint_thread field.
---
gdb/breakpoint.c | 39 +++++++++++++++++++++++++++++++++++++--
gdb/breakpoint.h | 5 +++++
2 files changed, 42 insertions(+), 2 deletions(-)
Index: src/gdb/breakpoint.h
===================================================================
--- src.orig/gdb/breakpoint.h 2009-11-20 00:07:15.000000000 +0000
+++ src/gdb/breakpoint.h 2009-11-20 00:15:39.000000000 +0000
@@ -457,6 +457,11 @@ struct breakpoint
should be evaluated on the outermost frame. */
struct frame_id watchpoint_frame;
+ /* Holds the thread which identifies the frame this watchpoint
+ should be considered in scope for, or `null_ptid' if the
+ watchpoint should be evaluated in all threads. */
+ ptid_t watchpoint_thread;
+
/* For hardware watchpoints, the triggered status according to the
hardware. */
enum watchpoint_triggered watchpoint_triggered;
Index: src/gdb/breakpoint.c
===================================================================
--- src.orig/gdb/breakpoint.c 2009-11-20 00:07:15.000000000 +0000
+++ src/gdb/breakpoint.c 2009-11-20 00:26:07.000000000 +0000
@@ -985,6 +985,23 @@ fetch_watchpoint_value (struct expressio
}
}
+/* Assuming that B is a watchpoint: returns true if the current thread
+ and its running state are safe to evaluate or update watchpoint B.
+ Watchpoints on local expressions need to evaluated in the context
+ of the thread that was current when the watchpoint was created,
+ and, that thread needs to be stopped to be able to select the
+ correct frame context. Watchpoints on global expressions can be
+ evaluated on any thread, and in any state. It is presently left to
+ the target allowing memory accesses when threads are running. */
+
+static int
+watchpoint_in_thread_scope (struct breakpoint *b)
+{
+ return (ptid_equal (b->watchpoint_thread, null_ptid)
+ || (ptid_equal (inferior_ptid, b->watchpoint_thread)
+ && !is_executing (inferior_ptid)));
+}
+
/* Assuming that B is a watchpoint:
- Reparse watchpoint expression, if REPARSE is non-zero
- Evaluate expression and store the result in B->val
@@ -1004,6 +1021,12 @@ update_watchpoint (struct breakpoint *b,
bpstat bs;
struct program_space *frame_pspace;
+ /* If this is a local watchpoint, we only want to check if the
+ watchpoint frame is in scope if the current thread is the thread
+ that was used to create the watchpoint. */
+ if (!watchpoint_in_thread_scope (b))
+ return;
+
/* We don't free locations. They are stored in bp_location array and
update_global_locations will eventually delete them and remove
breakpoints if needed. */
@@ -3085,6 +3108,12 @@ watchpoint_check (void *p)
b = bs->breakpoint_at->owner;
+ /* If this is a local watchpoint, we only want to check if the
+ watchpoint frame is in scope if the current thread is the thread
+ that was used to create the watchpoint. */
+ if (!watchpoint_in_thread_scope (b))
+ return WP_VALUE_NOT_CHANGED;
+
if (b->exp_valid_block == NULL)
within_current_scope = 1;
else
@@ -7151,9 +7180,15 @@ watch_command_1 (char *arg, int accessfl
b->cond_string = 0;
if (frame)
- b->watchpoint_frame = get_frame_id (frame);
+ {
+ b->watchpoint_frame = get_frame_id (frame);
+ b->watchpoint_thread = inferior_ptid;
+ }
else
- b->watchpoint_frame = null_frame_id;
+ {
+ b->watchpoint_frame = null_frame_id;
+ b->watchpoint_thread = null_ptid;
+ }
if (scope_breakpoint != NULL)
{
===================================================================
2009-11-19 Pedro Alves <pedro@codesourcery.com>
gdb/testsuite/
* local-watch-wrong-thread.c, local-watch-wrong-thread.exp: New
files.
---
gdb/testsuite/gdb.threads/local-watch-wrong-thread.c | 80 +++++++++++
gdb/testsuite/gdb.threads/local-watch-wrong-thread.exp | 118 +++++++++++++++++
2 files changed, 198 insertions(+)
Index: src/gdb/testsuite/gdb.threads/local-watch-wrong-thread.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ src/gdb/testsuite/gdb.threads/local-watch-wrong-thread.c 2009-11-19 01:10:15.000000000 +0000
@@ -0,0 +1,80 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2002, 2003, 2004, 2007, 2008, 2009 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 <unistd.h>
+#include <stdlib.h>
+#include <pthread.h>
+
+unsigned int args[2];
+int trigger = 0;
+
+void *
+thread_function0 (void *arg)
+{
+ int my_number = (long) arg;
+ volatile int *myp = (volatile int *) &args[my_number];
+
+ while (*myp > 0)
+ {
+ (*myp) ++;
+ usleep (1); /* Loop increment 1. */
+ }
+
+ return NULL;
+}
+
+void *
+thread_function1 (void *arg)
+{
+ int my_number = (long) arg;
+
+ volatile int *myp = (volatile int *) &args[my_number];
+
+ while (*myp > 0)
+ {
+ (*myp) ++;
+ usleep (1); /* Loop increment 2. */
+ }
+
+ return NULL;
+}
+
+int
+main ()
+{
+ int res;
+ pthread_t threads[2];
+ void *thread_result;
+ long i = 0;
+
+ args[i] = 1; /* Init value. */
+ res = pthread_create (&threads[i], NULL,
+ thread_function0,
+ (void *) i);
+
+ i++;
+ args[i] = 1; /* Init value. */
+ res = pthread_create(&threads[i], NULL,
+ thread_function1,
+ (void *) i);
+
+ pthread_join (threads[0], &thread_result);
+ pthread_join (threads[1], &thread_result);
+ exit(EXIT_SUCCESS);
+}
Index: src/gdb/testsuite/gdb.threads/local-watch-wrong-thread.exp
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ src/gdb/testsuite/gdb.threads/local-watch-wrong-thread.exp 2009-11-19 02:02:12.000000000 +0000
@@ -0,0 +1,118 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2004, 2007, 2008, 2009 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/>.
+
+# Check that GDB can support multiple watchpoints across threads.
+
+# This test verifies that a local watchpoint isn't deleted when a
+# thread other than the thread the local watchpoint was set in stops
+# for a breakpoint.
+if [target_info exists gdb,no_hardware_watchpoints] {
+ return 0;
+}
+
+set testfile "local-watch-wrong-thread"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+if {[gdb_compile_pthreads \
+ "${srcdir}/${subdir}/${srcfile}" \
+ "${binfile}" executable {debug} ] != "" } {
+ return -1
+}
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
+gdb_test "set can-use-hw-watchpoints 1" "" ""
+
+if ![runto_main] then {
+ fail "Can't run to main"
+ return
+}
+
+set inc_line_1 [gdb_get_line_number "Loop increment 1"]
+set inc_line_2 [gdb_get_line_number "Loop increment 2"]
+
+# Run to the loop within thread_function0, so we can set our local
+# watchpoint.
+gdb_test "break ${srcfile}:${inc_line_1}" \
+ "Breakpoint 2 at .*: file .*${srcfile}, line .*" \
+ "breakpoint on thread_function0"
+
+gdb_test "continue" \
+ ".*Breakpoint 2.*thread_function0.*" \
+ "continue to thread_function0"
+
+delete_breakpoints
+
+# Set the local watchpoint, and confirm that it traps as expected.
+gdb_test "watch *myp" \
+ "Hardware watchpoint 3\: \\*myp.*" \
+ "set local watchpoint on *myp"
+
+gdb_test "continue" \
+ "Hardware watchpoint.*Old value.*New value.*thread_function0.*" \
+ "local watchpoint triggers"
+
+delete_breakpoints
+
+# Recreate the watchpoint, but this time with a condition we know
+# won't trigger. This is so the watchpoint is inserted, and the
+# target reports events, but GDB doesn't stop for them. We want to
+# hit the breakpoints on the other thread, and make sure this
+# watchpoint isn't deleted then.
+gdb_test "watch *myp if trigger != 0" \
+ "Hardware watchpoint 4\: \\*myp.*" \
+ "set local watchpoint on *myp, with false conditional"
+
+# Run to a breakpoint on a different thread. The previous local
+# watchpoint should not be deleted with the standard 'the program has
+# left the block in which its expression is valid', because the
+# thread_function0 thread should still be running in the loop.
+gdb_test "break ${srcfile}:${inc_line_2}" \
+ "Breakpoint 5 at .*: file .*${srcfile}, line .*" \
+ "breakpoint on the other thread"
+
+gdb_test "continue" \
+ "Breakpoint 5, thread_function1.*" \
+ "the other thread stopped on breakpoint"
+
+# Delete the new breakpoint, we don't need it anymore.
+gdb_test "delete 5" "" ""
+
+# Check if the local watchpoint hasn't been deleted (is still listed).
+# This is simpler to check than expecting 'the program has left ...',
+# and, is immune to string changes in that warning.
+gdb_test "info breakpoints" \
+ ".*4.*hw watchpoint.*keep.*y.*\\*myp.*" \
+ "local watchpoint is still in breakpoint list"
+
+# Make the watchpoint condition eval true.
+gdb_test "set trigger=1" "" "let local watchpoint trigger"
+
+gdb_test "continue" \
+ "Hardware watchpoint.*Old value.*New value.*thread_function0.*" \
+ "local watchpoint still triggers"
+
+# Confirm that the local watchpoint is indeed deleted if
+# thread_function0 returns.
+gdb_test "set *myp=0" "" "let thread_function0 return"
+
+gdb_test "continue" \
+ ".*Watchpoint.*deleted.*" \
+ "local watchpoint automatically deleted"