From fb550a919a88bf4e3950dd7bcdf72f0a18d94206 Mon Sep 17 00:00:00 2001 From: Andrew Burgess Date: Thu, 10 Jun 2021 10:44:43 +0100 Subject: gdb: terminate upon receipt of SIGFPE GDB's SIGFPE handling is broken, this is PR gdb/16505 and PR gdb/17891. We currently try to use an async event token to process SIGFPE. So, when a SIGFPE arrives the signal handler calls mark_async_signal_handler then returns, effectively ignoring the signal (for now). The intention is that later the event loop will see that the async token associated with SIGFPE has been marked and will call the async handler, which just throws an error. The problem is that SIGFPE is not safe to ignore. Ignoring a SIGFPE (unless it is generated artificially, e.g. by raise()) is undefined behaviour, after ignoring the signal on many targets we return to the instruction that caused the SIGFPE to be raised, which immediately causes another SIGFPE to be raised, we get stuck in an infinite loop. The behaviour is certainly true on x86-64. To view this behaviour I simply added some dummy code to GDB that performed an integer divide by zero, compiled this on x86-64 GNU/Linux, ran GDB and saw GDB hang. In this commit, I propose to remove all special handling of SIGFPE and instead just let GDB make use of the default SIGFPE action, that is, to terminate the process. The only user visible change here should be: - If a user sends a SIGFPE to GDB using something like kill, previously GDB would just print an error and remain alive, now GDB will terminate. This is inline with what happens if the user sends GDB a SIGSEGV from kill though, so I don't see this as an issue. - If a bug in GDB causes a real SIGFPE, previously the users GDB session would hang. Now the GDB session will terminate. Again, this is inline with what happens if GDB receives a SIGSEGV due to an internal bug. In bug gdb/16505 there is mention that it would be nice if GDB did more than just terminate when receiving a fatal signal. I haven't done that in this commit, but later commits will move in that direction. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=16505 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=17891 --- gdb/event-top.c | 25 +------------------------ 1 file changed, 1 insertion(+), 24 deletions(-) diff --git a/gdb/event-top.c b/gdb/event-top.c index 002a7dc..ab5179b 100644 --- a/gdb/event-top.c +++ b/gdb/event-top.c @@ -58,7 +58,6 @@ static void handle_sigquit (int sig); #ifdef SIGHUP static void handle_sighup (int sig); #endif -static void handle_sigfpe (int sig); /* Functions to be invoked by the event loop in response to signals. */ @@ -68,7 +67,6 @@ static void async_do_nothing (gdb_client_data); #ifdef SIGHUP static void async_disconnect (gdb_client_data); #endif -static void async_float_handler (gdb_client_data); #ifdef SIGTSTP static void async_sigtstp_handler (gdb_client_data); #endif @@ -111,7 +109,6 @@ static struct async_signal_handler *sighup_token; #ifdef SIGQUIT static struct async_signal_handler *sigquit_token; #endif -static struct async_signal_handler *sigfpe_token; #ifdef SIGTSTP static struct async_signal_handler *sigtstp_token; #endif @@ -904,7 +901,7 @@ static struct serial_event *quit_serial_event; /* Initialization of signal handlers and tokens. There is a function handle_sig* for each of the signals GDB cares about. Specifically: - SIGINT, SIGFPE, SIGQUIT, SIGTSTP, SIGHUP, SIGWINCH. These + SIGINT, SIGQUIT, SIGTSTP, SIGHUP, SIGWINCH. These functions are the actual signal handlers associated to the signals via calls to signal(). The only job for these functions is to enqueue the appropriate event/procedure with the event loop. Such @@ -955,9 +952,6 @@ async_init_signals (void) sighup_token = create_async_signal_handler (async_do_nothing, NULL, "sighup"); #endif - signal (SIGFPE, handle_sigfpe); - sigfpe_token = - create_async_signal_handler (async_float_handler, NULL, "sigfpe"); #ifdef SIGTSTP sigtstp_token = @@ -1198,23 +1192,6 @@ async_sigtstp_handler (gdb_client_data arg) } #endif /* SIGTSTP */ -/* Tell the event loop what to do if SIGFPE is received. - See event-signal.c. */ -static void -handle_sigfpe (int sig) -{ - mark_async_signal_handler (sigfpe_token); - signal (sig, handle_sigfpe); -} - -/* Event loop will call this function to process a SIGFPE. */ -static void -async_float_handler (gdb_client_data arg) -{ - /* This message is based on ANSI C, section 4.7. Note that integer - divide by zero causes this, so "float" is a misnomer. */ - error (_("Erroneous arithmetic operation.")); -} /* Set things up for readline to be invoked via the alternate -- cgit v1.1