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[patchv3] Workaround gdbserver<7.7 for setfs

On Wed, 30 Mar 2016 16:17:11 +0200, Pedro Alves wrote:
> E.g., reading this I'm left wondering, did it always respond OK to
> unknown vFile packets, or to all unknown packets?  I think it was
> actually the latter.

To all vFile packets.  Other packets produce on gdbserver-7.6:
	Sending packet: $MustReplyEmpty#c4...Ack
	Packet received: E01

Is the patch OK for check-in this way?

2016-04-04  Jan Kratochvil  <>

	* remote.c (unknown_vfile_replies_ok): New variable.
	(packet_config_support): Read it.
	(remote_start_remote): Set it.

diff --git a/gdb/remote.c b/gdb/remote.c
index 5c407b6..8d949f6 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -1496,6 +1496,15 @@ enum {
 static struct packet_config remote_protocol_packets[PACKET_MAX];
+/* gdbserver < 7.7 (before its fix from 2013-12-11) did reply to any
+   unknown vFile packet with string "OK".  "OK" gets interpreted by GDB
+   as a reply to known packet.  For packet "vFile:setfs:" it is an
+   invalid reply and GDB would return error in
+   remote_hostio_set_filesystem, making remote files access impossible.
+   If this variable is non-zero it means the remote gdbserver is buggy
+   and any not yet detected packets are assumed as unsupported.  */
+static int unknown_vfile_replies_ok;
 /* Returns the packet's corresponding "set remote foo-packet" command
    state.  See struct packet_config for more details.  */
@@ -1519,6 +1528,9 @@ packet_config_support (struct packet_config *config)
       return PACKET_DISABLE;
+      if (unknown_vfile_replies_ok && config->name != NULL
+	  && startswith (config->name, "vFile:"))
       return config->support;
       gdb_assert_not_reached (_("bad switch"));
@@ -4023,6 +4035,21 @@ remote_start_remote (int from_tty, struct target_ops *target, int extended_p)
   if (packet_support (PACKET_QAllow) != PACKET_DISABLE)
     remote_set_permissions (target);
+  /* See unknown_vfile_replies_ok description.  */
+  {
+    const char vfile_mustreplyempty[] = "vFile:MustReplyEmpty:";
+    putpkt (vfile_mustreplyempty);
+    getpkt (&rs->buf, &rs->buf_size, 0);
+    if (strcmp (rs->buf, "OK") == 0)
+      unknown_vfile_replies_ok = 1;
+    else if (strcmp (rs->buf, "") == 0)
+      unknown_vfile_replies_ok = 0;
+    else
+      error (_("Remote replied unexpectedly to '%s': %s"), vfile_mustreplyempty,
+	     rs->buf);
+  }
   /* Next, we possibly activate noack mode.
      If the QStartNoAckMode packet configuration is set to AUTO,

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