Re: [PATCH v2] Fix signal unsafe call inside a signal

[Andrew Burgess <aburgess@redhat.com>]

Thank you for spotting and fixing this.

Bernd Edlinger <bernd.edlinger@hotmail.de> writes:

> As mentioned in
> https://sourceware.org/bugzilla/show_bug.cgi?id=31713#c9
> it can easily happen that the signal handler function
> handle_fatal_signal() uses various signal unsafe functions.
> Fix that by pre-computing the necessary language specific
> strings.
> ---
>  gdb/bt-utils.c  | 22 +++++++++++--
>  gdb/bt-utils.h  |  4 +++
>  gdb/event-top.c | 83 ++++++++++++++++++++++++++++++++++++++++++++-----
>  3 files changed, 99 insertions(+), 10 deletions(-)
>
> v2: moved initalization of language specific string to an init function
>
> diff --git a/gdb/bt-utils.c b/gdb/bt-utils.c
> index f658ce0d4bc..5626662a9c1 100644
> --- a/gdb/bt-utils.c
> +++ b/gdb/bt-utils.c
> @@ -125,6 +125,8 @@ gdb_internal_backtrace_1 ()
>  
>  /* See the comment on previous version of this function.  */
>  
> +static const char *str_backtrace_incomplete;
> +

You've placed this string between the comment and the function that the
comment applies too.

>  static void
>  gdb_internal_backtrace_1 ()
>  {
> @@ -139,12 +141,26 @@ gdb_internal_backtrace_1 ()
>  
>    backtrace_symbols_fd (buffer, frames, gdb_stderr->fd ());
>    if (frames == ARRAY_SIZE (buffer))
> -    sig_write (_("Backtrace might be incomplete.\n"));
> +    sig_write (str_backtrace_incomplete);
>  }
>  
>  #else
>  #error "unexpected internal backtrace policy"
>  #endif
> +
> +static const char *str_backtrace;
> +static const char *str_backtrace_unavailable;
> +
> +void
> +init_str_internal_backtrace ()

Rather than placing this initialisation into an extern function and then
calling it from event-top.c I think it would be better to place this
initialisation into a function like:

  void _initialize_bt_utils ();
  void
  _initialize_bt_utils ()
  {
    ...
  }

GDB will then take care of calling this automatically for you.  My
reasoning is that this breaks the dependency between the signal handling
setup and the backtrace utility function.

> +{
> +  str_backtrace = _("----- Backtrace -----\n");
> +  str_backtrace_unavailable = _("Backtrace unavailable\n");
> +#ifdef GDB_PRINT_INTERNAL_BACKTRACE_USING_EXECINFO
> +  str_backtrace_incomplete = _("Backtrace might be incomplete.\n");
> +#endif
> +}
> +
>  #endif /* GDB_PRINT_INTERNAL_BACKTRACE */
>  
>  /* See bt-utils.h.  */
> @@ -161,12 +177,12 @@ gdb_internal_backtrace ()
>      gdb_stderr->write_async_safe (msg, strlen (msg));
>    };
>  
> -  sig_write (_("----- Backtrace -----\n"));
> +  sig_write (str_backtrace);
>  
>    if (gdb_stderr->fd () > -1)
>      gdb_internal_backtrace_1 ();
>    else
> -    sig_write (_("Backtrace unavailable\n"));
> +    sig_write (str_backtrace_unavailable);
>  
>    sig_write ("---------------------\n");
>  #endif
> diff --git a/gdb/bt-utils.h b/gdb/bt-utils.h
> index ec2d14a5484..b6a7ef5464d 100644
> --- a/gdb/bt-utils.h
> +++ b/gdb/bt-utils.h
> @@ -71,4 +71,8 @@ extern void gdb_internal_backtrace ();
>  extern void gdb_internal_backtrace_set_cmd (const char *args, int from_tty,
>  					    cmd_list_element *c);
>  
> +#ifdef GDB_PRINT_INTERNAL_BACKTRACE
> +extern void init_str_internal_backtrace ();
> +#endif
> +
>  #endif /* BT_UTILS_H */

If you pick up the _initialize_bt_utils() approach then this will no
longer be needed.

> diff --git a/gdb/event-top.c b/gdb/event-top.c
> index b81970d11bb..02e21634ce5 100644
> --- a/gdb/event-top.c
> +++ b/gdb/event-top.c
> @@ -892,6 +892,50 @@ unblock_signal (int sig)
>    return false;
>  }
>  
> +/* Signal safe language specific strings.  */
> +
> +#ifdef GDB_PRINT_INTERNAL_BACKTRACE
> +static const char *str_fatal_signal;
> +static const char *str_sigsegv;
> +#ifdef SIGFPE
> +static const char *str_sigfpe;
> +#endif
> +#ifdef SIGBUS
> +static const char *str_sigbus;
> +#endif
> +#ifdef SIGABRT
> +static const char *str_sigabrt;
> +#endif
> +static const char *str_unknown_signal;
> +static const char *str_fatal_error_detected_gdb_will_now_terminate;
> +static const char *str_this_is_a_bug;
> +static const char *str_for_instructions_see;
> +
> +static void
> +init_str_handle_fatal_signal ()

Static functions should have a comment on them please.

> +{
> +  str_fatal_signal = _("Fatal signal: ");
> +  str_sigsegv = strsignal(SIGSEGV);
> +#ifdef SIGFPE
> +  str_sigfpe = strsignal(SIGFPE);
> +#endif
> +#ifdef SIGBUS
> +  str_sigbus = strsignal(SIGBUS);
> +#endif
> +#ifdef SIGABRT
> +  str_sigabrt = strsignal(SIGABRT);

Missing a space after strsignal and the '(' in 4 places above.

Thanks,
Andrew

> +#endif
> +  str_unknown_signal = _("Unknown signal");
> +  str_fatal_error_detected_gdb_will_now_terminate =
> +	_("A fatal error internal to GDB has been detected, "
> +	  "further\ndebugging is not possible.  GDB will now "
> +	  "terminate.\n\n");
> +  str_this_is_a_bug = _("This is a bug, please report it.");
> +  str_for_instructions_see = _("  For instructions, see:\n");
> +  init_str_internal_backtrace ();
> +}
> +#endif
> +
>  /* Called to handle fatal signals.  SIG is the signal number.  */
>  
>  static void ATTRIBUTE_NORETURN
> @@ -910,19 +954,40 @@ handle_fatal_signal (int sig)
>    if (bt_on_fatal_signal)
>      {
>        sig_write ("\n\n");
> -      sig_write (_("Fatal signal: "));
> -      sig_write (strsignal (sig));
> +      sig_write (str_fatal_signal);
> +      switch (sig)
> +	{
> +	case SIGSEGV:
> +	  sig_write (str_sigsegv);
> +	  break;
> +#ifdef SIGFPE
> +	case SIGFPE:
> +	  sig_write (str_sigfpe);
> +	  break;
> +#endif
> +#ifdef SIGBUS
> +	case SIGBUS:
> +	  sig_write (str_sigbus);
> +	  break;
> +#endif
> +#ifdef SIGABRT
> +	case SIGABRT:
> +	  sig_write (str_sigabrt);
> +	  break;
> +#endif
> +	default:
> +	  sig_write (str_unknown_signal);
> +	  break;
> +	}
>        sig_write ("\n");
>  
>        gdb_internal_backtrace ();
>  
> -      sig_write (_("A fatal error internal to GDB has been detected, "
> -		   "further\ndebugging is not possible.  GDB will now "
> -		   "terminate.\n\n"));
> -      sig_write (_("This is a bug, please report it."));
> +      sig_write (str_fatal_error_detected_gdb_will_now_terminate);
> +      sig_write (str_this_is_a_bug);
>        if (REPORT_BUGS_TO[0] != '\0')
>  	{
> -	  sig_write (_("  For instructions, see:\n"));
> +	  sig_write (str_for_instructions_see);
>  	  sig_write (REPORT_BUGS_TO);
>  	  sig_write (".");
>  	}
> @@ -1050,6 +1115,10 @@ gdb_init_signals (void)
>      create_async_signal_handler (async_sigtstp_handler, NULL, "sigtstp");
>  #endif
>  
> +#ifdef GDB_PRINT_INTERNAL_BACKTRACE
> +  init_str_handle_fatal_signal ();
> +#endif
> +
>  #ifdef SIGFPE
>    signal (SIGFPE, handle_fatal_signal);
>  #endif
> -- 
> 2.39.2