Re: [External] : Re: [PATCH v4] gdb : Signal to pstack/gdb kills the attached process.

[Partha Satapathy <partha.satapathy@oracle.com>]

On 3/7/2024 3:28 PM, Partha Satapathy wrote:
> Author: Partha Sarathi Satapathy <partha.satapathy@oracle.com>
> Date:   Fri Nov 17 09:18:56 2023 +0000
> 
> gdb : Signal to pstack/gdb kills the attached process.
> 
> Problem: While gdb is attaching an inferior, if ctrl-c is pressed in the
> middle of the process attach,  the sigint is passed to the debugged
> process. This triggers the exit of the inferior. For example in pstack,
> printing a stack can take significant time, and ctrl-c is pressed to
> abort the pstack/gdb application. This in turn kills the debugged
> process, which can be critical for the system. In this case, the
> intention of ctrl+c is to kill pstack/gdb, but not the inferior
> application.
> gdb -p <<pid>>
> or gdb /proc/<<pid>>/exe pid
> Attaching to process
> << ctrl+c is pressed during attach
> (gdb) q
> <<<< inferior process exited >>>>
> 
> A Ctrl-C/sigint received by gdb during the attachment of an inferior
> passed to the debugged at some definite points during the window of
> process attachment. The process of attaching an inferior is a multistep
> process, and it takes time to get ready with the GDB prompt. As the
> debugger and debugger are not fully attached during this period, the
> sigint takes its default action to terminate the process.
> 
> Solution: While GDB attaches processes, the inferior is not the current
> session leader. Hence, until attach is complete and the GDB prompt is
> available, the sigint should not be passed to the inferior.
> The signal should be skipped if the process runs in the background. With
> this approach, we can skip passing the signature if the process is
> attached to the GDB and the process attach is not complete.
> 
> Reviewed-By: Guinevere Larsen <blarsen@redhat.com>
> ---
>   gdb/infcmd.c   | 2 ++
>   gdb/inferior.h | 3 +++
>   gdb/target.c   | 3 +++
>   3 files changed, 8 insertions(+)
> 
> diff --git a/gdb/infcmd.c b/gdb/infcmd.c
> index c1fdbb300c67..8ab2d50477f4 100644
> --- a/gdb/infcmd.c
> +++ b/gdb/infcmd.c
> @@ -2528,6 +2528,8 @@ enum async_reply_reason
>     target_post_attach (inferior_ptid.pid ());
> 
>     post_create_inferior (from_tty);
> +  current_inferior ()->sync_flag = true;
> +  check_quit_flag();
>   }
> 
>   /* What to do after the first program stops after attaching.  */
> diff --git a/gdb/inferior.h b/gdb/inferior.h
> index 7be28423aeb1..a6065da19a87 100644
> --- a/gdb/inferior.h
> +++ b/gdb/inferior.h
> @@ -600,6 +600,9 @@ class inferior : public refcounted_object,
>     /* True if this child process was attached rather than forked.  */
>     bool attach_flag = false;
> 
> +  /* True if inferior has been fully synced and prompt is no longer 
> blocked */
> +  bool sync_flag = false;
> +
>     /* If this inferior is a vfork child, then this is the pointer to
>        its vfork parent, if GDB is still attached to it.  */
>     inferior *vfork_parent = NULL;
> diff --git a/gdb/target.c b/gdb/target.c
> index bbc1badc9e19..7c7df9c2ed87 100644
> --- a/gdb/target.c
> +++ b/gdb/target.c
> @@ -3794,6 +3794,9 @@ struct target_ops *
>                   through the target_stack.  */
>                scoped_restore_current_inferior restore_inferior;
>                set_current_inferior (inf);
> +             if ((current_inferior ()->attach_flag)
> +               && !(current_inferior ()->sync_flag))
> +                 return;
>                current_inferior ()->top_target ()->pass_ctrlc ();
>                return;
>              }