Suppress SIGTTOU when handling errors

[ Backport of commit 766f883622. ]

Calls to error () can cause SIGTTOU to send gdb to the background.

For example, on an Arm build:
  (gdb) b main
  Breakpoint 1 at 0x10774: file /build/gdb/testsuite/../../../src/binutils-gdb/gdb/testsuite/gdb.base/watchpoint.c, line 174.
  (gdb) r
  Starting program: /build/gdb/testsuite/outputs/gdb.base/watchpoint/watchpoint

  [1]+  Stopped                 ../gdb ./outputs/gdb.base/watchpoint/watchpoint
  localhost$ fg
  ../gdb ./outputs/gdb.base/watchpoint/watchpoint
  Cannot parse expression `.L1199 4@r4'.
  warning: Probes-based dynamic linker interface failed.
  Reverting to original interface.

The SIGTTOU is raised whilst inside a syscall during the call to tcdrain.
Fix is to use scoped_ignore_sigttou to ensure SIGTTOU is blocked.

In addition fix include comments - job_control is not included via terminal.h

gdb/ChangeLog:

	* event-top.c: Remove include comment.
	* inflow.c (class scoped_ignore_sigttou): Move from here...
	* inflow.h (class scoped_ignore_sigttou): ...to here.
	* ser-unix.c (hardwire_drain_output): Block SIGTTOU during drain.
	* top.c:  Remove include comment.

gdb/ChangeLog

@@ -1,3 +1,11 @@
+2019-05-28  Alan Hayward  <alan.hayward@arm.com>
+
+	* event-top.c: Remove include comment.
+	* inflow.c (class scoped_ignore_sigttou): Move from here...
+	* inflow.h (class scoped_ignore_sigttou): ...to here.
+	* ser-unix.c (hardwire_drain_output): Block SIGTTOU during drain.
+	* top.c:  Remove include comment.
+
 2019-08-04  Alan Hayward  <alan.hayward@arm.com>
 
 	* symfile.c (symbol_file_command): Call solib_create_inferior_hook.

gdb/event-top.c

@@ -24,7 +24,7 @@
 #include "inferior.h"
 #include "infrun.h"
 #include "target.h"
-#include "terminal.h"		/* for job_control */
+#include "terminal.h"
 #include "event-loop.h"
 #include "event-top.h"
 #include "interps.h"

gdb/inflow.c

@@ -103,35 +103,6 @@ static serial_ttystate initial_gdb_ttystate;
 
 static struct terminal_info *get_inflow_inferior_data (struct inferior *);
 
-/* RAII class used to ignore SIGTTOU in a scope.  */
-
-class scoped_ignore_sigttou
-{
-public:
-  scoped_ignore_sigttou ()
-  {
-#ifdef SIGTTOU
-    if (job_control)
-      m_osigttou = signal (SIGTTOU, SIG_IGN);
-#endif
-  }
-
-  ~scoped_ignore_sigttou ()
-  {
-#ifdef SIGTTOU
-    if (job_control)
-      signal (SIGTTOU, m_osigttou);
-#endif
-  }
-
-  DISABLE_COPY_AND_ASSIGN (scoped_ignore_sigttou);
-
-private:
-#ifdef SIGTTOU
-  sighandler_t m_osigttou = NULL;
-#endif
-};
-
 /* While the inferior is running, we want SIGINT and SIGQUIT to go to the
    inferior only.  If we have job control, that takes care of it.  If not,
    we save our handlers in these two variables and set SIGINT and SIGQUIT

gdb/inflow.h

@@ -21,5 +21,36 @@
 #define INFLOW_H
 
 #include <unistd.h>
+#include <signal.h>
+#include "common/job-control.h"
+
+/* RAII class used to ignore SIGTTOU in a scope.  */
+
+class scoped_ignore_sigttou
+{
+public:
+  scoped_ignore_sigttou ()
+  {
+#ifdef SIGTTOU
+    if (job_control)
+      m_osigttou = signal (SIGTTOU, SIG_IGN);
+#endif
+  }
+
+  ~scoped_ignore_sigttou ()
+  {
+#ifdef SIGTTOU
+    if (job_control)
+      signal (SIGTTOU, m_osigttou);
+#endif
+  }
+
+  DISABLE_COPY_AND_ASSIGN (scoped_ignore_sigttou);
+
+private:
+#ifdef SIGTTOU
+  sighandler_t m_osigttou = NULL;
+#endif
+};
 
 #endif /* inflow.h */

gdb/ser-unix.c

@@ -32,6 +32,7 @@
 #include "gdbcmd.h"
 #include "common/filestuff.h"
 #include <termios.h>
+#include "inflow.h"
 
 struct hardwire_ttystate
   {
@@ -164,6 +165,9 @@ hardwire_print_tty_state (struct serial *scb,
 static int
 hardwire_drain_output (struct serial *scb)
 {
+  /* Ignore SIGTTOU which may occur during the drain.  */
+  scoped_ignore_sigttou ignore_sigttou;
+
   return tcdrain (scb->fd);
 }
 

gdb/top.c

@@ -34,7 +34,7 @@
 #include "expression.h"
 #include "value.h"
 #include "language.h"
-#include "terminal.h"		/* For job_control.  */
+#include "terminal.h"
 #include "common/job-control.h"
 #include "annotate.h"
 #include "completer.h"