[PATCH v3 1/1] gdb, breakpoint: add a destructor to the watchpoint struct

[PATCH v3 1/1] gdb, breakpoint: add a destructor to the watchpoint struct

[Mohamed Bouhaouel]

Make sure to unlink the related breakpoint when the watchpoint instance
is deleted.  This prevents having a wp-related breakpoint that is
linked to a NULL watchpoint (e.g.  the watchpoint instance is being
deleted when the 'watch' command fails).  With the below scenario,
having such a left out breakpoint will lead to a GDB hang, and this
is due to an infinite loop when deleting all inferior breakpoints.

Scenario:
	(gdb) set can-use-hw-watchpoints 0
	(gdb) awatch <SCOPE VAR>
	Can't set read/access watchpoint when hardware watchpoints are disabled.
	(gdb) rwatch <SCOPE VAR>
	Can't set read/access watchpoint when hardware watchpoints are disabled.
	(gdb) <continue the program until the end>
	>> HANG <<

Signed-off-by: Mohamed Bouhaouel <mohamed.bouhaouel@intel.com>
Reviewed-by: Bruno Larsen <blarsen@redhat.com>
---
 gdb/breakpoint.c                              | 14 +++++++
 gdb/breakpoint.h                              |  3 ++
 .../gdb.base/scope-hw-watch-disable.c         | 26 ++++++++++++
 .../gdb.base/scope-hw-watch-disable.exp       | 40 +++++++++++++++++++
 4 files changed, 83 insertions(+)
 create mode 100644 gdb/testsuite/gdb.base/scope-hw-watch-disable.c
 create mode 100644 gdb/testsuite/gdb.base/scope-hw-watch-disable.exp

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index da6c8de9d14..8e14b3ba939 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -9597,6 +9597,20 @@ break_range_command (const char *arg, int from_tty)
   install_breakpoint (false, std::move (br), true);
 }
 
+/* See breakpoint.h.  */
+
+watchpoint::~watchpoint ()
+{
+  /* Make sure to unlink the destroyed watchpoint from the related
+     breakpoint ring.  */
+
+  breakpoint *bpt = this;
+  while (bpt->related_breakpoint != this)
+    bpt = bpt->related_breakpoint;
+
+  bpt->related_breakpoint = this->related_breakpoint;
+}
+
 /*  Return non-zero if EXP is verified as constant.  Returned zero
     means EXP is variable.  Also the constant detection may fail for
     some constant expressions and in such case still falsely return
diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
index da150585f73..2de3fcec823 100644
--- a/gdb/breakpoint.h
+++ b/gdb/breakpoint.h
@@ -992,6 +992,9 @@ struct watchpoint : public breakpoint
   void print_recreate (struct ui_file *fp) const override;
   bool explains_signal (enum gdb_signal) override;
 
+  /* Destructor for WATCHPOINT.  */
+  ~watchpoint ();
+
   /* String form of exp to use for displaying to the user (malloc'd),
      or NULL if none.  */
   gdb::unique_xmalloc_ptr<char> exp_string;
diff --git a/gdb/testsuite/gdb.base/scope-hw-watch-disable.c b/gdb/testsuite/gdb.base/scope-hw-watch-disable.c
new file mode 100644
index 00000000000..30956fe1b84
--- /dev/null
+++ b/gdb/testsuite/gdb.base/scope-hw-watch-disable.c
@@ -0,0 +1,26 @@
+/* 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
+main ()
+{
+  int a = 0, b = 0;
+  b = a;
+  a = b + 10;
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/scope-hw-watch-disable.exp b/gdb/testsuite/gdb.base/scope-hw-watch-disable.exp
new file mode 100644
index 00000000000..54ebb4e4226
--- /dev/null
+++ b/gdb/testsuite/gdb.base/scope-hw-watch-disable.exp
@@ -0,0 +1,40 @@
+# 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/>.
+
+# Test that GDB displays the correct error message when hardware watchpoints
+# are not supported or explicitly disabled.  Test also that GDB terminates
+# successfully after several attempts to insert a hardware watchpoint.
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
+    return -1
+}
+
+gdb_test_no_output "set can-use-hw-watchpoints 0"
+
+if {![runto_main]} {
+    return -1
+}
+
+gdb_test "awatch a" \
+    "Can't set read/access watchpoint when hardware watchpoints are disabled." \
+    "unsuccessful attempt to create an access watchpoint"
+gdb_test "rwatch b" \
+    "Can't set read/access watchpoint when hardware watchpoints are disabled." \
+    "unsuccessful attempt to create a read watchpoint"
+
+# The program continues until termination.
+gdb_continue_to_end
-- 
2.25.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

RE: [PING][PATCH v3 1/1] gdb, breakpoint: add a destructor to the watchpoint struct

[Bouhaouel, Mohamed]

Dear all,

I kindly request that you review this patch.

Thanks,
-Mohamed

> -----Original Message-----
> From: Bouhaouel, Mohamed <mohamed.bouhaouel@intel.com>
> Sent: Friday, June 30, 2023 10:10 AM
> To: gdb-patches@sourceware.org
> Cc: blarsen@redhat.com; aburgess@redhat.com; tom@tromey.com; Bouhaouel,
> Mohamed <mohamed.bouhaouel@intel.com>
> Subject: [PATCH v3 1/1] gdb, breakpoint: add a destructor to the watchpoint
> struct
> 
> Make sure to unlink the related breakpoint when the watchpoint instance
> is deleted.  This prevents having a wp-related breakpoint that is
> linked to a NULL watchpoint (e.g.  the watchpoint instance is being
> deleted when the 'watch' command fails).  With the below scenario,
> having such a left out breakpoint will lead to a GDB hang, and this
> is due to an infinite loop when deleting all inferior breakpoints.
> 
> Scenario:
> 	(gdb) set can-use-hw-watchpoints 0
> 	(gdb) awatch <SCOPE VAR>
> 	Can't set read/access watchpoint when hardware watchpoints are
> disabled.
> 	(gdb) rwatch <SCOPE VAR>
> 	Can't set read/access watchpoint when hardware watchpoints are
> disabled.
> 	(gdb) <continue the program until the end>
> 	>> HANG <<
> 
> Signed-off-by: Mohamed Bouhaouel <mohamed.bouhaouel@intel.com>
> Reviewed-by: Bruno Larsen <blarsen@redhat.com>
> ---
>  gdb/breakpoint.c                              | 14 +++++++
>  gdb/breakpoint.h                              |  3 ++
>  .../gdb.base/scope-hw-watch-disable.c         | 26 ++++++++++++
>  .../gdb.base/scope-hw-watch-disable.exp       | 40 +++++++++++++++++++
>  4 files changed, 83 insertions(+)
>  create mode 100644 gdb/testsuite/gdb.base/scope-hw-watch-disable.c
>  create mode 100644 gdb/testsuite/gdb.base/scope-hw-watch-disable.exp
> 
> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
> index da6c8de9d14..8e14b3ba939 100644
> --- a/gdb/breakpoint.c
> +++ b/gdb/breakpoint.c
> @@ -9597,6 +9597,20 @@ break_range_command (const char *arg, int
> from_tty)
>    install_breakpoint (false, std::move (br), true);
>  }
> 
> +/* See breakpoint.h.  */
> +
> +watchpoint::~watchpoint ()
> +{
> +  /* Make sure to unlink the destroyed watchpoint from the related
> +     breakpoint ring.  */
> +
> +  breakpoint *bpt = this;
> +  while (bpt->related_breakpoint != this)
> +    bpt = bpt->related_breakpoint;
> +
> +  bpt->related_breakpoint = this->related_breakpoint;
> +}
> +
>  /*  Return non-zero if EXP is verified as constant.  Returned zero
>      means EXP is variable.  Also the constant detection may fail for
>      some constant expressions and in such case still falsely return
> diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
> index da150585f73..2de3fcec823 100644
> --- a/gdb/breakpoint.h
> +++ b/gdb/breakpoint.h
> @@ -992,6 +992,9 @@ struct watchpoint : public breakpoint
>    void print_recreate (struct ui_file *fp) const override;
>    bool explains_signal (enum gdb_signal) override;
> 
> +  /* Destructor for WATCHPOINT.  */
> +  ~watchpoint ();
> +
>    /* String form of exp to use for displaying to the user (malloc'd),
>       or NULL if none.  */
>    gdb::unique_xmalloc_ptr<char> exp_string;
> diff --git a/gdb/testsuite/gdb.base/scope-hw-watch-disable.c
> b/gdb/testsuite/gdb.base/scope-hw-watch-disable.c
> new file mode 100644
> index 00000000000..30956fe1b84
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/scope-hw-watch-disable.c
> @@ -0,0 +1,26 @@
> +/* 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
> +main ()
> +{
> +  int a = 0, b = 0;
> +  b = a;
> +  a = b + 10;
> +
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.base/scope-hw-watch-disable.exp
> b/gdb/testsuite/gdb.base/scope-hw-watch-disable.exp
> new file mode 100644
> index 00000000000..54ebb4e4226
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/scope-hw-watch-disable.exp
> @@ -0,0 +1,40 @@
> +# 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/>.
> +
> +# Test that GDB displays the correct error message when hardware watchpoints
> +# are not supported or explicitly disabled.  Test also that GDB terminates
> +# successfully after several attempts to insert a hardware watchpoint.
> +
> +standard_testfile
> +
> +if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
> +    return -1
> +}
> +
> +gdb_test_no_output "set can-use-hw-watchpoints 0"
> +
> +if {![runto_main]} {
> +    return -1
> +}
> +
> +gdb_test "awatch a" \
> +    "Can't set read/access watchpoint when hardware watchpoints are disabled."
> \
> +    "unsuccessful attempt to create an access watchpoint"
> +gdb_test "rwatch b" \
> +    "Can't set read/access watchpoint when hardware watchpoints are disabled."
> \
> +    "unsuccessful attempt to create a read watchpoint"
> +
> +# The program continues until termination.
> +gdb_continue_to_end
> --
> 2.25.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

Re: [PING][PATCH v3 1/1] gdb, breakpoint: add a destructor to the watchpoint struct

[Tom Tromey]

>>>>> Bouhaouel, Mohamed via Gdb-patches <gdb-patches@sourceware.org> writes:

> I kindly request that you review this patch.

Thank you for the patch.

>> +/* See breakpoint.h.  */
>> +
>> +watchpoint::~watchpoint ()
>> +{
>> +  /* Make sure to unlink the destroyed watchpoint from the related
>> +     breakpoint ring.  */
>> +
>> +  breakpoint *bpt = this;
>> +  while (bpt->related_breakpoint != this)
>> +    bpt = bpt->related_breakpoint;
>> +
>> +  bpt->related_breakpoint = this->related_breakpoint;

It took me a while to understand this, but I guess it is just the same
as the code in delete_breakpoint.

I think this is ok.
Approved-By: Tom Tromey <tom@tromey.com>

Tom

RE: [PING][PATCH v3 1/1] gdb, breakpoint: add a destructor to the watchpoint struct

[Bouhaouel, Mohamed]

Hi Tom,

Thanks a lot for your review.  This is my first accepted patch
in GDB.  Can you please push it for me?  I don't have any write access.

I plan to upstream more patches in the future and would like to have
"write after approval" access.  I guess I need to apply for access
in this form https://sourceware.org/cgi-bin/pdw/ps_form.cgi, after
my first patch is pushed!

Thanks again,
Mohamed


> -----Original Message-----
> From: Tom Tromey <tom@tromey.com>
> Sent: Friday, September 15, 2023 7:46 PM
> To: Bouhaouel, Mohamed via Gdb-patches <gdb-patches@sourceware.org>
> Cc: Bouhaouel, Mohamed <mohamed.bouhaouel@intel.com>; tom@tromey.com
> Subject: Re: [PING][PATCH v3 1/1] gdb, breakpoint: add a destructor to the
> watchpoint struct
> 
> >>>>> Bouhaouel, Mohamed via Gdb-patches <gdb-patches@sourceware.org>
> writes:
> 
> > I kindly request that you review this patch.
> 
> Thank you for the patch.
> 
> >> +/* See breakpoint.h.  */
> >> +
> >> +watchpoint::~watchpoint ()
> >> +{
> >> +  /* Make sure to unlink the destroyed watchpoint from the related
> >> +     breakpoint ring.  */
> >> +
> >> +  breakpoint *bpt = this;
> >> +  while (bpt->related_breakpoint != this)
> >> +    bpt = bpt->related_breakpoint;
> >> +
> >> +  bpt->related_breakpoint = this->related_breakpoint;
> 
> It took me a while to understand this, but I guess it is just the same
> as the code in delete_breakpoint.
> 
> I think this is ok.
> Approved-By: Tom Tromey <tom@tromey.com>
> 
> Tom
Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

Re: [PING][PATCH v3 1/1] gdb, breakpoint: add a destructor to the watchpoint struct

[Tom Tromey]

> Thanks a lot for your review.  This is my first accepted patch
> in GDB.  Can you please push it for me?  I don't have any write access.

I pushed it.

> I plan to upstream more patches in the future and would like to have
> "write after approval" access.  I guess I need to apply for access
> in this form https://sourceware.org/cgi-bin/pdw/ps_form.cgi, after
> my first patch is pushed!

Yeah.  You can use me as the referrer.
Once you have access you have to update the MAINTAINERS file.

thanks,
Tom