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

["Bouhaouel, Mohamed" <mohamed.bouhaouel@intel.com>]

Thanks Andrew for your feedback.

> > Scenario:
> > 	(gdb) awatch <VAR>
> > 	Target does not support this type of hardware watchpoint.
> > 	(gdb) rwatch <VAR>
> > 	Target does not support this type of hardware watchpoint.
> > 	(gdb) <continue the program until the end>
> > 	>> HANG <<
> >
> 
> Is it not possible to create a test case based on this scenario?

It is difficult to produce such scenario due to a weird behavior [1],
which needs to be addressed as well.  As a result, deleting watchpoints
before resuming would hide the issue.


[1] When the watch command fails, it is not possible to resume
unless we explicitly delete the watchpoint.  More details can be
found here:
https://sourceware.org/pipermail/gdb-patches/2023-March/198371.html)

Kind regards,
Mohamed



> -----Original Message-----
> From: Andrew Burgess <aburgess@redhat.com>
> Sent: Tuesday, April 4, 2023 1:38 PM
> To: Bouhaouel, Mohamed <mohamed.bouhaouel@intel.com>; gdb-
> patches@sourceware.org
> Subject: Re: [PATCH 1/1] gdb, breakpoint: add a destructor to the watchpoint
> struct
> 
> Mohamed Bouhaouel via Gdb-patches <gdb-patches@sourceware.org>
> writes:
> 
> > 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) awatch <VAR>
> > 	Target does not support this type of hardware watchpoint.
> > 	(gdb) rwatch <VAR>
> > 	Target does not support this type of hardware watchpoint.
> > 	(gdb) <continue the program until the end>
> > 	>> HANG <<
> >
> 
> Is it not possible to create a test case based on this scenario?
> 
> Thanks,
> Andrew
> 
> > Signed-off-by: Mohamed Bouhaouel <mohamed.bouhaouel@intel.com>
> > ---
> >  gdb/breakpoint.c | 15 +++++++++++++++
> >  gdb/breakpoint.h |  3 +++
> >  2 files changed, 18 insertions(+)
> >
> > diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
> > index 7228acfd8fe..b9ddc85c30c 100644
> > --- a/gdb/breakpoint.c
> > +++ b/gdb/breakpoint.c
> > @@ -9581,6 +9581,21 @@ 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;
> > +  breakpoint *related = bpt;
> > +  while (related->related_breakpoint != bpt)
> > +    related = related->related_breakpoint;
> > +
> > +  related->related_breakpoint = bpt->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 7c5cf3f2bef..4f19e42dd83 100644
> > --- a/gdb/breakpoint.h
> > +++ b/gdb/breakpoint.h
> > @@ -933,6 +933,9 @@ struct watchpoint : public breakpoint
> >    void print_recreate (struct ui_file *fp) const override;
> >    bool explains_signal (enum gdb_signal) override;
> >
> > +  /* Destructor for WATCHPOINT.  */
> > +  virtual ~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;
> > --
> > 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

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