PATCH? gdb remote.c: readchar() should pop_target() if SERIAL_ERROR?

[Oleg Nesterov <oleg@redhat.com>]

Hello.

I was trying to learn how gdb works with gdbserver and hit the bug.
The patch below seems to fix the problem for me but I am not sure
it is correct, I never looked into the (complex!) gdb sources before.

In short, sometimes gdb doing "target remote :tcp_port" refuses to
exit, putpkt_binary() complains that putpkt failed and longjmp()s
to the main loop. This happens sometimes if gdbserver dies.

	(gdb) q
	A debugging session is active.

		Inferior 1 [Remote target] will be killed.

	Quit anyway? (y or n) y
	putpkt: write failed: Broken pipe.
	(gdb)

Not sure my analysis is correct, but I think that readchar() needs
a fix. A read/recv from a socket doesn't necessarily returns EOF if
the peer has closed the socket. It can return sock->sk_err set by
the previous send if the peer dies and sets sk->sk_shutdown.

The patch merely adds pop_target(). The more sophisticates fix
should probably continue the reading, sock->sk_err was cleared and
the socket may have the packets which we could read.

Oleg.

--- gdb-7.1/gdb/remote.c~	2010-03-07 15:39:53.000000000 +0100
+++ gdb-7.1/gdb/remote.c	2010-07-02 02:38:09.000000000 +0200
@@ -6364,6 +6364,7 @@ readchar (int timeout)
       error (_("Remote connection closed"));
       /* no return */
     case SERIAL_ERROR:
+      pop_target ();
       perror_with_name (_("Remote communication error"));
       /* no return */
     case SERIAL_TIMEOUT: