[PATCH] Add 'reverse' capability query to remote protocol (qSupported).

[Michael Snyder <msnyder@vmware.com>]

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Following discussion, this patch adds feature capability handling
(enable, disable, and automatic "qSupported" query) for the reverse
execution packets "bs" (backward step) and "bc" (backward continue
in the gdb remote protocol.

Cc:ing Jakob and Greg, whose remote targets may be affected.
What you guys will want to do is have your remote targets
recognize the "qSupported" query from gdb, and respond with:

	ReverseContinue+;ReverseStep+

This will tell gdb that your targets support those two commands.

Otherwise, they default to "disabled", and a user would need
to enable them with these commands (which might be added to a
.gdbinit file):

	set remote reverse-continue on
	set remote reverse-step on

Pedro, does this look like what you expected?

Michael


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2009-08-31  Michael Snyder  <msnyder@vmware.com>

	* remote.c (PACKET_bc, PACKET_bs): New enums.
	(remote_protocol_features): Add ReverseStep, ReverseContinue.
	(remote_resume): Check for reverse capability.
	(_initialize_remote): Add packet config for "bs" and "bc" packets.

Index: remote.c
===================================================================
RCS file: /cvs/src/src/gdb/remote.c,v
retrieving revision 1.370
diff -u -p -r1.370 remote.c
--- remote.c	18 Aug 2009 16:17:16 -0000	1.370
+++ remote.c	31 Aug 2009 19:55:21 -0000
@@ -1000,6 +1000,8 @@ enum {
   PACKET_qXfer_siginfo_write,
   PACKET_qAttached,
   PACKET_ConditionalTracepoints,
+  PACKET_bc,
+  PACKET_bs,
   PACKET_MAX
 };
 
@@ -3051,6 +3053,10 @@ static struct protocol_feature remote_pr
     PACKET_qXfer_siginfo_write },
   { "ConditionalTracepoints", PACKET_DISABLE, remote_cond_tracepoint_feature,
     PACKET_ConditionalTracepoints },
+  { "ReverseContinue", PACKET_DISABLE, remote_supported_packet,
+    PACKET_bc },
+  { "ReverseStep", PACKET_DISABLE, remote_supported_packet,
+    PACKET_bs },
 };
 
 static void
@@ -3818,6 +3824,14 @@ remote_resume (struct target_ops *ops,
       if (info_verbose && siggnal != TARGET_SIGNAL_0)
 	warning (" - Can't pass signal %d to target in reverse: ignored.\n",
 		 siggnal);
+
+      if (step &&
+	  remote_protocol_packets[PACKET_bs].support == PACKET_DISABLE)
+	error ("Remote reverse-step not supported.");
+      if (!step &&
+	  remote_protocol_packets[PACKET_bc].support == PACKET_DISABLE)
+	error ("Remote reverse-continue not supported.");
+
       strcpy (buf, step ? "bs" : "bc");
     }
   else if (siggnal != TARGET_SIGNAL_0)
@@ -9165,6 +9179,12 @@ Show the maximum size of the address (in
 			 "qGetTLSAddr", "get-thread-local-storage-address",
 			 0);
 
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_bc],
+			 "bc", "reverse-continue", 0);
+
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_bs],
+			 "bs", "reverse-step", 0);
+
   add_packet_config_cmd (&remote_protocol_packets[PACKET_qSupported],
 			 "qSupported", "supported-packets", 0);