[PATCH 1/2] [GDBserver] Check input interrupt after reading in a packet

[Yao Qi <qiyaoltc@gmail.com>]

GDBserver may read some packet together with '\003' in one go.  We've
already checked '\003' first when reading packet by my patch,

  Check input interrupt first when reading packet
  https://sourceware.org/ml/gdb-patches/2016-01/msg00057.html

but if we don't check '\003' *after* each packet, the interrupt will
be processed next time GDBserver reads from the buffer, so that the
interrupt isn't processed in time.  For example, GDB sends vCont;c and
interrupt (see gdb.base/interrupt-noterm.exp), we'll resume the
inferior and wait once packet vCont;c is seen.  If we don't check the
interrupt character after vCont;c packet, interrupt character will stay
in the buffer unattended until GDBserver returns from the wait, which
may take a while.  Note that since we've read '\003' from file
descriptor, SIGIO signal handler input_interrupt doesn't help either.

This issue can be exposed by hacking the end of getpkt like
@@ -1041,6 +1050,9 @@ getpkt (char *buf)
        }
     }

+  if (readchar_bufcnt > 0)
+    gdb_assert (*readchar_bufp != '\003');
+
   return bp - buf;
 }

and this can trigger internal error,
(gdb) PASS: gdb.base/interrupt-noterm.exp: interrupt
Remote connection closed^M
(gdb) FAIL: gdb.base/interrupt-noterm.exp: inferior received SIGINT
Remote debugging from host 10.2.206.40^M
/home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/remote-utils.c:1054: A problem internal to GDBserver has been detected.^M
getpkt: Assertion `*readchar_bufp != '\003'' failed.^M

This patch is to peek the buffer, if it is '\003', consume it and call
*the_target->request_interrupt.

gdb/gdbserver:

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.
---
 gdb/gdbserver/remote-utils.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/gdb/gdbserver/remote-utils.c b/gdb/gdbserver/remote-utils.c
index 292197a..000457d 100644
--- a/gdb/gdbserver/remote-utils.c
+++ b/gdb/gdbserver/remote-utils.c
@@ -1041,6 +1041,15 @@ getpkt (char *buf)
 	}
     }
 
+  /* The '\003' may appear after some packet, and check it in the buffer,
+     so that we can process the interrupt in time.  */
+  if (readchar_bufcnt > 0 && *readchar_bufp == '\003')
+    {
+      /* Consume the interrupt character in the buffer.  */
+      readchar ();
+      (*the_target->request_interrupt) ();
+    }
+
   return bp - buf;
 }
 
-- 
1.9.1