[GDBserver] Check input interrupt after reading in a packet

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.

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 2e94aa88bfb47765cab632caa082eeed21dca501..4aa7350db38b58aa1fd1bf01d8d8911067958026 100644 (file)
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+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.
+
 2016-01-25  Yao Qi  <yao.qi@linaro.org>
 
        * remote-utils.c (new_thread_notify): Remove.

diff --git a/gdb/gdbserver/remote-utils.c b/gdb/gdbserver/remote-utils.c
index 292197a4c924dba897ac7c2ff5687988de639f1a..ccc99f16a2f84da132e714c7bcd0b23c18cd580f 100644 (file)
--- a/gdb/gdbserver/remote-utils.c
+++ b/gdb/gdbserver/remote-utils.c
@@ -1041,6 +1041,22 @@ getpkt (char *buf)
        }
     }
 
+  /* The readchar above may have already read a '\003' out of the socket
+     and moved it to the local buffer.  For example, when GDB sends
+     vCont;c immediately followed by interrupt (see
+     gdb.base/interrupt-noterm.exp).  As soon as we see the vCont;c, we'll
+     resume the inferior and wait.  Since we've already moved the '\003'
+     to the local buffer, SIGIO won't help.  In that case, if we don't
+     check for interrupt after the vCont;c packet, the interrupt character
+     would stay in the buffer unattended until after the next (unrelated)
+     stop.  */
+  while (readchar_bufcnt > 0 && *readchar_bufp == '\003')
+    {
+      /* Consume the interrupt character in the buffer.  */
+      readchar ();
+      (*the_target->request_interrupt) ();
+    }
+
   return bp - buf;
 }