Eliminate STOP_SIGNAL, use SIGTSTP directly

The STOP_SIGNAL macro was originally added for Convex Unix
(https://en.wikipedia.org/wiki/Convex_Computer).

In:

  git show 7a67dd45ca1c:gdb/m-convex.h

we see:

~~~
  /* Use SIGCONT rather than SIGTSTP because convex Unix occasionally
     turkeys SIGTSTP.  I think.  */

  #define STOP_SIGNAL SIGCONT
~~~

That's gdb-3.5, 1990...  In gdb/ChangeLog-3.x we see:

~~~
Tue Apr 18 13:43:37 1989  Randall Smith  (randy at apple-gunkies.ai.mit.edu)

        Various changes involved in 1) getting gdb to work on the convex,
	[...]
        Made whatever signal indicates a stop configurable (via macro
        STOP_SIGNAL).
        (main): Setup use of above as a signal handler.  Added check for
        "-nw" in args already processed.
        (command_line_input): SIGTSTP ==>STOP_SIGNAL.
~~~

Support for Convex Unix is long gone, and nothing else overrides
STOP_SIGNAL.  So just use SIGTSTP directly, removing a little
obfuscation.

(I don't really understand why we override [1] readline's SIGTSTP
handler (only) when reading scripts (and then fail to restore it
properly, assuming SIG_DFL...), but I'll leave that for another pass.

[1] - Actually, starting with readline 6.3, readline is no longer
installing its handlers while GDB is in control...)

gdb/ChangeLog:
2017-11-06  Pedro Alves  <palves@redhat.com>

	* event-top.c: Check SIGTSTP instead of STOP_SIGNAL thoughout.
	(async_init_signals): Adjust.
	(handle_stop_sig): Rename to ...
	(handle_sigtstp): ... this.
	(async_stop_sig): Rename to ...
	(async_sigtstp_handler): ... this, and delete STOP_SIGNAL !=
	SIGTSTP path.
	* event-top.h: Move signal.h include to the top.  Check SIGTSTP
	instead of STOP_SIGNAL thoughout.
	(handle_stop_sig): Rename to ...
	(handle_sigtstp): ... this.
	* top.c (command_line_input): Replace STOP_SIGNAL -> SIGTSTP.

1 files changed, 11 insertions, 15 deletions

diff --git a/gdb/event-top.c b/gdb/event-top.c
index 43e2a27..7377189 100644
--- a/gdb/event-top.c
+++ b/gdb/event-top.c
@@ -68,8 +68,8 @@ static void async_do_nothing (gdb_client_data);
 static void async_disconnect (gdb_client_data);
 #endif
 static void async_float_handler (gdb_client_data);
-#ifdef STOP_SIGNAL
-static void async_stop_sig (gdb_client_data);
+#ifdef SIGTSTP
+static void async_sigtstp_handler (gdb_client_data);
 #endif
 static void async_sigterm_handler (gdb_client_data arg);
 
@@ -111,7 +111,7 @@ static struct async_signal_handler *sighup_token;
 static struct async_signal_handler *sigquit_token;
 #endif
 static struct async_signal_handler *sigfpe_token;
-#ifdef STOP_SIGNAL
+#ifdef SIGTSTP
 static struct async_signal_handler *sigtstp_token;
 #endif
 static struct async_signal_handler *async_sigterm_token;
@@ -912,9 +912,9 @@ async_init_signals (void)
   sigfpe_token =
     create_async_signal_handler (async_float_handler, NULL);
 
-#ifdef STOP_SIGNAL
+#ifdef SIGTSTP
   sigtstp_token =
-    create_async_signal_handler (async_stop_sig, NULL);
+    create_async_signal_handler (async_sigtstp_handler, NULL);
 #endif
 }
 
@@ -1112,20 +1112,19 @@ async_disconnect (gdb_client_data arg)
 }
 #endif
 
-#ifdef STOP_SIGNAL
+#ifdef SIGTSTP
 void
-handle_stop_sig (int sig)
+handle_sigtstp (int sig)
 {
   mark_async_signal_handler (sigtstp_token);
-  signal (sig, handle_stop_sig);
+  signal (sig, handle_sigtstp);
 }
 
 static void
-async_stop_sig (gdb_client_data arg)
+async_sigtstp_handler (gdb_client_data arg)
 {
   char *prompt = get_prompt ();
 
-#if STOP_SIGNAL == SIGTSTP
   signal (SIGTSTP, SIG_DFL);
 #if HAVE_SIGPROCMASK
   {
@@ -1138,10 +1137,7 @@ async_stop_sig (gdb_client_data arg)
   sigsetmask (0);
 #endif
   raise (SIGTSTP);
-  signal (SIGTSTP, handle_stop_sig);
-#else
-  signal (STOP_SIGNAL, handle_stop_sig);
-#endif
+  signal (SIGTSTP, handle_sigtstp);
   printf_unfiltered ("%s", prompt);
   gdb_flush (gdb_stdout);
 
@@ -1149,7 +1145,7 @@ async_stop_sig (gdb_client_data arg)
      nothing.  */
   dont_repeat ();
 }
-#endif /* STOP_SIGNAL */
+#endif /* SIGTSTP */
 
 /* Tell the event loop what to do if SIGFPE is received.
    See event-signal.c.  */