[RFA] Reverse Debugging, 2/5

[Michael Snyder <msnyder@vmware.com>]

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This patch (#2) adds a target implementation of reverse debugging
(for the "remote" target), implementing the new target_ops methods
and changing remote_wait and remote_resume to make use of them.

Adding this patch on top of patch #1 causes no change in gdb
behavior, since nothing invokes the new methods.  Tested under
RHEL native with no change in results.


2008-09-30  Michael Snyder  <msnyder@vmware.com>
	Remote interface for reverse debugging.
	* remote.c (remote_get_execdir, remote_set_execdir): New methods.
	(remote_vcont_resume): Jump out if attempting reverse execution.
	(remote_resume): Check for reverse exec direction, and send
	appropriate command to target.
	(remote_wait): Check target response for NO_HISTORY status.
	Also check for empty reply (target doesn't understand "bs" or "bc).
	(_initialize_remote): Add new methods to remote target vector.

Index: remote.c
===================================================================
RCS file: /cvs/src/src/gdb/remote.c,v
retrieving revision 1.310
diff -u -p -r1.310 remote.c
--- remote.c	22 Sep 2008 15:21:30 -0000	1.310
+++ remote.c	30 Sep 2008 18:23:30 -0000
@@ -3385,7 +3385,15 @@ remote_resume (ptid_t ptid, int step, en
     set_continue_thread (ptid);
 
   buf = rs->buf;
-  if (siggnal != TARGET_SIGNAL_0)
+  if (target_get_execution_direction () == EXEC_REVERSE)
+    {
+      /* We don't pass signals to the target in reverse exec mode.  */
+      if (info_verbose && siggnal != TARGET_SIGNAL_0)
+	warning (" - Can't pass signal %d to target in reverse: ignored.\n",
+		 siggnal);
+      strcpy (buf, step ? "bs" : "bc");
+    }
+  else if (siggnal != TARGET_SIGNAL_0)
     {
       buf[0] = step ? 'S' : 'C';
       buf[1] = tohex (((int) siggnal >> 4) & 0xf);
@@ -3651,8 +3659,15 @@ remote_wait (ptid_t ptid, struct target_
 	  /* We're out of sync with the target now.  Did it continue or not?
 	     Not is more likely, so report a stop.  */
 	  warning (_("Remote failure reply: %s"), buf);
-	  status->kind = TARGET_WAITKIND_STOPPED;
-	  status->value.sig = TARGET_SIGNAL_0;
+	  if (buf[1] == '0' && buf[2] == '6')
+	    {
+	      status->kind = TARGET_WAITKIND_NO_HISTORY;
+	    }
+	  else
+	    {
+	      status->kind = TARGET_WAITKIND_STOPPED;
+	      status->value.sig = TARGET_SIGNAL_0;
+	    }
 	  goto got_status;
 	case 'F':		/* File-I/O request.  */
 	  remote_fileio_request (buf);
@@ -7545,6 +7560,35 @@ remote_command (char *args, int from_tty
   help_list (remote_cmdlist, "remote ", -1, gdb_stdout);
 }
 
+/* Reverse execution.
+   TODO: set up as a capability.  */
+static enum exec_direction_kind remote_execdir = EXEC_FORWARD;
+
+static enum exec_direction_kind remote_get_execdir (void)
+{
+  if (remote_debug && info_verbose)
+    printf_filtered ("remote execdir is %s\n",
+		     remote_execdir == EXEC_FORWARD ? "forward" :
+		     remote_execdir == EXEC_REVERSE ? "reverse" :
+		     "unknown");
+  return remote_execdir;
+}
+
+static int remote_set_execdir (enum exec_direction_kind dir)
+{
+  if (remote_debug && info_verbose)
+    printf_filtered ("Set remote execdir: %s\n",
+		     dir == EXEC_FORWARD ? "forward" :
+		     dir == EXEC_REVERSE ? "reverse" :
+		     "bad direction");
+
+  /* TODO: check target for capability.  */
+  if (dir == EXEC_FORWARD || dir == EXEC_REVERSE)
+    return (remote_execdir = dir);
+  else
+    return EXEC_ERROR;
+}
+
 static void
 init_remote_ops (void)
 {
@@ -7593,6 +7637,8 @@ Specify the serial device it is connecte
   remote_ops.to_has_registers = 1;
   remote_ops.to_has_execution = 1;
   remote_ops.to_has_thread_control = tc_schedlock;	/* can lock scheduler */
+  remote_ops.to_get_execdir = remote_get_execdir;
+  remote_ops.to_set_execdir = remote_set_execdir;
   remote_ops.to_magic = OPS_MAGIC;
   remote_ops.to_memory_map = remote_memory_map;
   remote_ops.to_flash_erase = remote_flash_erase;