[PATCH] Supress SIGTTOU when handling errors

[Alan Hayward <Alan dot Hayward at arm dot com>]

[I've seen this on and off over many months on AArch64 and Arm, and am
assuming it isn't the intended behaviour. Not sure if this should be at
tcdrain or it should be done at a higher level - eg in the terminal
handling code]

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:

2019-05-15  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.
---
 gdb/event-top.c |  2 +-
 gdb/inflow.c    | 29 -----------------------------
 gdb/inflow.h    | 31 +++++++++++++++++++++++++++++++
 gdb/ser-unix.c  |  4 ++++
 gdb/top.c       |  2 +-
 5 files changed, 37 insertions(+), 31 deletions(-)

diff --git a/gdb/event-top.c b/gdb/event-top.c
index 3ccf136ff1..93b7d2d28b 100644
--- a/gdb/event-top.c
+++ b/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"
diff --git a/gdb/inflow.c b/gdb/inflow.c
index 339b55c0bc..eba7a931f4 100644
--- a/gdb/inflow.c
+++ b/gdb/inflow.c
@@ -106,35 +106,6 @@ 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
diff --git a/gdb/inflow.h b/gdb/inflow.h
index c32aa14433..5dd5c37bd2 100644
--- a/gdb/inflow.h
+++ b/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 */
diff --git a/gdb/ser-unix.c b/gdb/ser-unix.c
index 5a9965bf74..3492619f2d 100644
--- a/gdb/ser-unix.c
+++ b/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);
 }
 
diff --git a/gdb/top.c b/gdb/top.c
index bacd684dba..1e17ebee87 100644
--- a/gdb/top.c
+++ b/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"
-- 
2.20.1 (Apple Git-117)