[PUSHED] PR gdb/17096: async support breaks remote debugging on Windows

[PUSHED] PR gdb/17096: async support breaks remote debugging on Windows

[Pedro Alves]

On Windows, with "maint set target-async on" (the default since
a09dd441), Ctrl-C fails to stop a remote target.

With maint target-async on, the SIGINT signal handler doesn't send the
remote interrupt request immediately.  Instead, it marks an async
handler as ready, and then the main event loop wakes up and notices
that the SIGINT async signal handler token was set, and calls the
corresponding event handler, which sends the remote interrupt request.

On POSIX-like systems, the SIGINT signal makes the select/poll in the
main event loop wake up / return with EINTR.  However, on Windows,
signal handlers run on a separate thread, and Windows doesn't really
have a concept of EINTR.  So, just marking the async handler
(effectively just setting a flag) does not wake up gdb_select.
Instead, we need to call gdb_call_async_signal_handler from the signal
handler.  The Windows version (in mingw-hdep.c) sets a Windows event
that gdb_select's WaitForMultipleObjects is waiting for.

Confirmed that with this, Ctrl-C interrupts the remote target on
Windows.  Also regression tested on x86_64 Fedora 20 against
GDBserver.

gdb/
2014-07-07  Pedro Alves  <palves@redhat.com>

	gdb/17096
	* remote.c (async_handle_remote_sigint)
	(async_handle_remote_sigint_twice): Call
	gdb_call_async_signal_handler instead of
	mark_async_signal_handler.
---
 gdb/ChangeLog | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 513a919..cb7185e 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -6,6 +6,14 @@
 	gdb_call_async_signal_handler instead of
 	mark_async_signal_handler.
 
+2014-07-07  Pedro Alves  <palves@redhat.com>
+
+	PR gdb/17096
+	* remote.c (async_handle_remote_sigint)
+	(async_handle_remote_sigint_twice): Call
+	gdb_call_async_signal_handler instead of
+	mark_async_signal_handler.
+
 2014-07-07  Tom Tromey  <tromey@redhat.com>
 
 	* target-delegates.c: Rebuild.
-- 
1.9.3

Re: [PUSHED] PR gdb/17096: async support breaks remote debugging on Windows

[Joel Brobecker]

> gdb/
> 2014-07-07  Pedro Alves  <palves@redhat.com>
> 
> 	gdb/17096
> 	* remote.c (async_handle_remote_sigint)
> 	(async_handle_remote_sigint_twice): Call
> 	gdb_call_async_signal_handler instead of
> 	mark_async_signal_handler.

It looks like the remote.c patch was missing, and since I looked it
up to take a look, I thought I might as well provide it here as well!
Thanks for working on this one, Pedro.

-- 
Joel

diff --git a/gdb/remote.c b/gdb/remote.c
index b6f3ddb..3aa030c 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -4818,7 +4818,9 @@ static void
 async_handle_remote_sigint (int sig)
 {
   signal (sig, async_handle_remote_sigint_twice);
-  mark_async_signal_handler (async_sigint_remote_token);
+  /* Note we need to go through gdb_call_async_signal_handler in order
+     to wake up the event loop on Windows.  */
+  gdb_call_async_signal_handler (async_sigint_remote_token, 0);
 }
 
 /* Signal handler for SIGINT, installed after SIGINT has already been
@@ -4828,7 +4830,8 @@ static void
 async_handle_remote_sigint_twice (int sig)
 {
   signal (sig, async_handle_remote_sigint);
-  mark_async_signal_handler (async_sigint_remote_twice_token);
+  /* See note in async_handle_remote_sigint.  */
+  gdb_call_async_signal_handler (async_sigint_remote_twice_token, 0);
 }
 
 /* Perform the real interruption of the target execution, in response

Re: [PUSHED] PR gdb/17096: async support breaks remote debugging on Windows

[Pedro Alves]

On 07/07/2014 09:30 PM, Joel Brobecker wrote:
>> gdb/
>> 2014-07-07  Pedro Alves  <palves@redhat.com>
>>
>> 	gdb/17096
>> 	* remote.c (async_handle_remote_sigint)
>> 	(async_handle_remote_sigint_twice): Call
>> 	gdb_call_async_signal_handler instead of
>> 	mark_async_signal_handler.
> 
> It looks like the remote.c patch was missing, and since I looked it
> up to take a look, I thought I might as well provide it here as well!
> Thanks for working on this one, Pedro.

Thanks Joel!

-- 
Pedro Alves