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

Yao Qi
2016-01-26T13:55:01Z

Pedro Alves <palves@redhat.com> writes:

> I'd suggest factoring out this duplicate sigprocmask handling,
> like, say, rename unblock_async_io and add a parameter:
>
> /* Block or unblock SIGIO. */
>
> static void
> block_unblock_async_io (int block)
> {
> #ifndef USE_WIN32API
> sigset_t sigio_set;
>
> sigemptyset (&sigio_set);
> sigaddset (&sigio_set, SIGIO);
> sigprocmask (block ? SIG_BLOCK : SIG_UNBLOCK, &sigio_set, NULL);
> #endif
> }

Done.

>
>> 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 ();
>
> I think it's safer practice to block the signal before
> installing the handler.

OK, and fixed.

>
> Otherwise LGTM.

Patch below is pushed in.

--
Yao (齐尧)
From 8b2073398477b33d425b0570236fe4e4222fe2c4 Mon Sep 17 00:00:00 2001
From: Yao Qi <yao.qi@linaro.org>
Date: Tue, 26 Jan 2016 13:50:22 +0000
Subject: [PATCH] [GDBserver] Block and unblock SIGIO

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): Rename to ...
(block_unblock_async_io): ... it. New function.
(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.

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 4aa7350..0ba902e 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,5 +1,16 @@
2016-01-26 Yao Qi <yao.qi@linaro.org>

+ * remote-utils.c (remote_close) [!USE_WIN32API]: Ignore SIGIO.
+ (unblock_async_io): Rename to ...
+ (block_unblock_async_io): ... it. New function.
+ (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.
+
+2016-01-26 Yao Qi <yao.qi@linaro.org>
+
* remote-utils.c (getpkt): If the buffer isn't empty, and the
first character is '\003', call *the_target->request_interrupt.

diff --git a/gdb/gdbserver/remote-utils.c b/gdb/gdbserver/remote-utils.c
index ccc99f1..e751473 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
@@ -775,19 +780,19 @@ 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. */
+/* 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. */

static void
-unblock_async_io (void)
+block_unblock_async_io (int block)
{
#ifndef USE_WIN32API
sigset_t sigio_set;

sigemptyset (&sigio_set);
sigaddset (&sigio_set, SIGIO);
- sigprocmask (SIG_UNBLOCK, &sigio_set, NULL);
+ sigprocmask (block ? SIG_BLOCK : SIG_UNBLOCK, &sigio_set, NULL);
#endif
}

@@ -823,9 +828,8 @@ enable_async_io (void)
if (async_io_enabled)
return;

-#ifndef USE_WIN32API
- signal (SIGIO, input_interrupt);
-#endif
+ block_unblock_async_io (0);
+
async_io_enabled = 1;
#ifdef __QNX__
nto_comctrl (1);
@@ -839,9 +843,8 @@ disable_async_io (void)
if (!async_io_enabled)
return;

-#ifndef USE_WIN32API
- signal (SIGIO, SIG_IGN);
-#endif
+ block_unblock_async_io (1);
+
async_io_enabled = 0;
#ifdef __QNX__
nto_comctrl (0);
@@ -852,12 +855,14 @@ disable_async_io (void)
void
initialize_async_io (void)
{
- /* Make sure that async I/O starts disabled. */
+ /* Make sure that async I/O starts blocked. */
async_io_enabled = 1;
disable_async_io ();

- /* Make sure the signal is unblocked. */
- unblock_async_io ();
+ /* Install the signal handler. */
+#ifndef USE_WIN32API
+ signal (SIGIO, input_interrupt);
+#endif
}

/* Internal buffer used by readchar.