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

[Andrew Burgess <aburgess@redhat.com>]

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
>
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