[PATCH 2/2] [GDBserver] Block and unblock SIGIO

[Yao Qi <qiyaoltc at gmail dot com>]

Nowadays, GDBserver disables async io (by ignoring SIGIO) when process
a serial event, and enables async io (by installing signal handler) when
resume the inferior and wait.  GDBserver may miss SIGIO (by interrupt)
and doesn't process SIGIO in time, which is shown by
gdb.base/interrupt-noterm.exp.  In the test, GDB sends "continue &" and
then "interrupt".  if '\003' arrives at a period between GDBserver
receives vCont;c and enables async io, SIGIO is ignored because signal
handler isn't installed.  GDBserver waits for the inferior and can not
notice '\003' until it returns from wait.

This patch changes the code to install SIGIO handler early, but block
and unblock SIGIO as needed.  In this way, we don't remove SIGIO
handler, so SIGIO can't be ignored.  However, GDBserver needs to
remove the signal handler when connection is closed.

gdb/gdbserver:

2016-01-26  Yao Qi  <yao.qi@linaro.org>

	* remote-utils.c (remote_close) [!USE_WIN32API]: Ignore SIGIO.
	(unblock_async_io): Remove.
	(enable_async_io): Don't install SIGIO handler.  Unblock it
	instead.
	(disable_async_io): Don't ignore SIGIO.  Block it instead.
	(initialize_async_io): Install SIGIO handler.  Don't call
	unblock_async_io.
---
 gdb/gdbserver/remote-utils.c | 51 ++++++++++++++++++++++++++------------------
 1 file changed, 30 insertions(+), 21 deletions(-)

diff --git a/gdb/gdbserver/remote-utils.c b/gdb/gdbserver/remote-utils.c
index 000457d..541675a 100644
--- a/gdb/gdbserver/remote-utils.c
+++ b/gdb/gdbserver/remote-utils.c
@@ -402,6 +402,11 @@ remote_close (void)
 {
   delete_file_handler (remote_desc);
 
+#ifndef USE_WIN32API
+  /* Remove SIGIO handler.  */
+  signal (SIGIO, SIG_IGN);
+#endif
+
 #ifdef USE_WIN32API
   closesocket (remote_desc);
 #else
@@ -775,21 +780,9 @@ check_remote_input_interrupt_request (void)
   input_interrupt (0);
 }
 
-/* Asynchronous I/O support.  SIGIO must be enabled when waiting, in order to
-   accept Control-C from the client, and must be disabled when talking to
-   the client.  */
-
-static void
-unblock_async_io (void)
-{
-#ifndef USE_WIN32API
-  sigset_t sigio_set;
-
-  sigemptyset (&sigio_set);
-  sigaddset (&sigio_set, SIGIO);
-  sigprocmask (SIG_UNBLOCK, &sigio_set, NULL);
-#endif
-}
+/* Asynchronous I/O support.  SIGIO must be unblocked when waiting,
+   in order to accept Control-C from the client, and must be blocked
+   when talking to the client.  */
 
 #ifdef __QNX__
 static void
@@ -820,12 +813,19 @@ static int async_io_enabled;
 void
 enable_async_io (void)
 {
+#ifndef USE_WIN32API
+  sigset_t sigio_set;
+#endif
+
   if (async_io_enabled)
     return;
 
 #ifndef USE_WIN32API
-  signal (SIGIO, input_interrupt);
+  sigemptyset (&sigio_set);
+  sigaddset (&sigio_set, SIGIO);
+  sigprocmask (SIG_UNBLOCK, &sigio_set, NULL);
 #endif
+
   async_io_enabled = 1;
 #ifdef __QNX__
   nto_comctrl (1);
@@ -836,12 +836,19 @@ enable_async_io (void)
 void
 disable_async_io (void)
 {
+#ifndef USE_WIN32API
+  sigset_t sigio_set;
+#endif
+
   if (!async_io_enabled)
     return;
 
 #ifndef USE_WIN32API
-  signal (SIGIO, SIG_IGN);
+  sigemptyset (&sigio_set);
+  sigaddset (&sigio_set, SIGIO);
+  sigprocmask (SIG_BLOCK, &sigio_set, NULL);
 #endif
+
   async_io_enabled = 0;
 #ifdef __QNX__
   nto_comctrl (0);
@@ -852,12 +859,14 @@ disable_async_io (void)
 void
 initialize_async_io (void)
 {
-  /* Make sure that async I/O starts disabled.  */
+  /* Install the signal handler.  */
+#ifndef USE_WIN32API
+  signal (SIGIO, input_interrupt);
+#endif
+
+  /* Make sure that async I/O starts blocked.  */
   async_io_enabled = 1;
   disable_async_io ();
-
-  /* Make sure the signal is unblocked.  */
-  unblock_async_io ();
 }
 
 /* Internal buffer used by readchar.
-- 
1.9.1