This patch (#3) adds to the infrun event loop so that it 
knows what to do differently if execution-direction is
reverse.  This effectively makes reverse step, next, 
and continue work properly, except that there is no way
for them to be invoked (that comes in a later patch).

This patch can go in on top of #1 and #2 without any
user-visible changes.  Tested under RHEL native with 
no change in results.


2008-09-30  Michael Snyder  <msnyder@vmware.com>
	Event handling interface for reverse debugging.
	* infrun.c (enum inferior_stop_reason): Add NO_HISTORY reason.
	(handle_inferior_event): Handle TARGET_WAITKIND_NO_HISTORY.
	Handle stepping over a function call in reverse.
	Handle stepping thru a line range in reverse.
	Handle setting a step-resume breakpoint in reverse.
	Handle stepping into a function in reverse.
	Handle stepping between line ranges in reverse.
	(print_stop_reason): Print reason for NO_HISTORY.

Index: infrun.c
===================================================================
RCS file: /cvs/src/src/gdb/infrun.c,v
retrieving revision 1.322
retrieving revision 1.322.2.2
diff -u -p -r1.322 -r1.322.2.2
--- infrun.c	22 Sep 2008 15:26:53 -0000	1.322
+++ infrun.c	30 Sep 2008 23:50:51 -0000	1.322.2.2
@@ -1193,11 +1193,17 @@ proceed (CORE_ADDR addr, enum target_sig
 
   if (addr == (CORE_ADDR) -1)
     {
-      if (pc == stop_pc && breakpoint_here_p (pc))
+      if (pc == stop_pc && breakpoint_here_p (pc) 
+	  && target_get_execution_direction () != EXEC_REVERSE)
 	/* There is a breakpoint at the address we will resume at,
 	   step one instruction before inserting breakpoints so that
 	   we do not stop right away (and report a second hit at this
-	   breakpoint).  */
+	   breakpoint).
+
+	   Note, we don't do this in reverse, because we won't
+	   actually be executing the breakpoint insn anyway.
+	   We'll be (un-)executing the previous instruction.  */
+
 	oneproc = 1;
       else if (gdbarch_single_step_through_delay_p (gdbarch)
 	       && gdbarch_single_step_through_delay (gdbarch,
@@ -1426,7 +1432,9 @@ enum inferior_stop_reason
   /* Inferior exited. */
   EXITED,
   /* Inferior received signal, and user asked to be notified. */
-  SIGNAL_RECEIVED
+  SIGNAL_RECEIVED,
+  /* Reverse execution -- target ran out of history info.  */
+  NO_HISTORY
 };
 
 /* The PTID we'll do a target_wait on.*/
@@ -2141,6 +2149,12 @@ handle_inferior_event (struct execution_
       ecs->event_thread->stop_signal = ecs->ws.value.sig;
       break;
 
+    case TARGET_WAITKIND_NO_HISTORY:
+      /* Reverse execution: target ran out of history info.  */
+      print_stop_reason (NO_HISTORY, 0);
+      stop_stepping (ecs);
+      return;
+
       /* We had an event in the inferior, but we are not interested
          in handling it at this level. The lower layers have already
          done what needs to be done, if anything.
@@ -2861,6 +2875,17 @@ infrun: BPSTAT_WHAT_SET_LONGJMP_RESUME (
 	    keep_going (ecs);
 	    return;
 	  }
+	if (stop_pc == ecs->stop_func_start &&
+	    target_get_execution_direction () == EXEC_REVERSE)
+	  {
+	    /* We are stepping over a function call in reverse, and
+	       just hit the step-resume breakpoint at the start
+	       address of the function.  Go back to single-stepping,
+	       which should take us back to the function call.  */
+	    ecs->event_thread->stepping_over_breakpoint = 1;
+	    keep_going (ecs);
+	    return;
+	  }
 	break;
 
       case BPSTAT_WHAT_CHECK_SHLIBS:
@@ -3026,10 +3051,25 @@ infrun: BPSTAT_WHAT_SET_LONGJMP_RESUME (
       && stop_pc < ecs->event_thread->step_range_end)
     {
       if (debug_infrun)
-	 fprintf_unfiltered (gdb_stdlog, "infrun: stepping inside range [0x%s-0x%s]\n",
+	fprintf_unfiltered (gdb_stdlog, "infrun: stepping inside range [0x%s-0x%s]\n",
 			    paddr_nz (ecs->event_thread->step_range_start),
 			    paddr_nz (ecs->event_thread->step_range_end));
-      keep_going (ecs);
+
+      /* When stepping backward, stop at beginning of line range
+	 (unles it's the function entry point, in which case
+	 keep going back to the call point).  */
+      if (stop_pc == ecs->event_thread->step_range_start &&
+	  stop_pc != ecs->stop_func_start &&
+	  target_get_execution_direction () == EXEC_REVERSE)
+	{
+	  ecs->event_thread->stop_step = 1;
+	  print_stop_reason (END_STEPPING_RANGE, 0);
+	  stop_stepping (ecs);
+	}
+      else
+	{
+	  keep_going (ecs);
+	}
       return;
     }
 
@@ -3116,10 +3156,28 @@ infrun: BPSTAT_WHAT_SET_LONGJMP_RESUME (
 
       if (ecs->event_thread->step_over_calls == STEP_OVER_ALL)
 	{
-	  /* We're doing a "next", set a breakpoint at callee's return
-	     address (the address at which the caller will
-	     resume).  */
-	  insert_step_resume_breakpoint_at_caller (get_current_frame ());
+	  /* We're doing a "next".
+
+	     Normal (forward) execution: set a breakpoint at the
+	     callee's return address (the address at which the caller
+	     will resume).
+
+	     Reverse (backward) execution.  set the step-resume
+	     breakpoint at the start of the function that we just
+	     stepped into (backwards), and continue to there.  When we
+	     get there, we'll need to single-step back to the
+	     caller.  */
+
+	  if (target_get_execution_direction () == EXEC_REVERSE)
+	    {
+	      struct symtab_and_line sr_sal;
+	      init_sal (&sr_sal);
+	      sr_sal.pc = ecs->stop_func_start;
+	      insert_step_resume_breakpoint_at_sal (sr_sal, null_frame_id);
+	    }
+	  else
+	    insert_step_resume_breakpoint_at_caller (get_current_frame ());
+
 	  keep_going (ecs);
 	  return;
 	}
@@ -3176,9 +3234,21 @@ infrun: BPSTAT_WHAT_SET_LONGJMP_RESUME (
 	  return;
 	}
 
-      /* Set a breakpoint at callee's return address (the address at
-         which the caller will resume).  */
-      insert_step_resume_breakpoint_at_caller (get_current_frame ());
+      if (target_get_execution_direction () == EXEC_REVERSE)
+	{
+	  /* Set a breakpoint at callee's start address.
+	     From there we can step once and be back in the caller.  */
+	  struct symtab_and_line sr_sal;
+	  init_sal (&sr_sal);
+	  sr_sal.pc = ecs->stop_func_start;
+	  insert_step_resume_breakpoint_at_sal (sr_sal, null_frame_id);
+	}
+      else
+	{
+	  /* Set a breakpoint at callee's return address (the address
+	     at which the caller will resume).  */
+	  insert_step_resume_breakpoint_at_caller (get_current_frame ());
+	}
       keep_going (ecs);
       return;
     }
@@ -3344,6 +3414,28 @@ step_into_function (struct execution_con
     ecs->stop_func_start = gdbarch_skip_prologue
 			     (current_gdbarch, ecs->stop_func_start);
 
+  if (target_get_execution_direction () == EXEC_REVERSE)
+    {
+      stop_func_sal = find_pc_line (stop_pc, 0);
+
+      /* OK, we're just gonna keep stepping here.  */
+      if (stop_func_sal.pc == stop_pc)
+	{
+	  /* We're there already.  Just stop stepping now.  */
+	  ecs->event_thread->stop_step = 1;
+	  print_stop_reason (END_STEPPING_RANGE, 0);
+	  stop_stepping (ecs);
+	  return;
+	}
+      /* Else just reset the step range and keep going.
+	 No step-resume breakpoint, they don't work for
+	 epilogues, which can have multiple entry paths.  */
+      ecs->event_thread->step_range_start = stop_func_sal.pc;
+      ecs->event_thread->step_range_end   = stop_func_sal.end;
+      keep_going (ecs);
+      return;
+    }
+  /* else... */
   stop_func_sal = find_pc_line (ecs->stop_func_start, 0);
   /* Use the step_resume_break to step until the end of the prologue,
      even if that involves jumps (as it seems to on the vax under
@@ -3712,6 +3804,10 @@ print_stop_reason (enum inferior_stop_re
       annotate_signal_string_end ();
       ui_out_text (uiout, ".\n");
       break;
+    case NO_HISTORY:
+      /* Reverse execution: target ran out of history info.  */
+      ui_out_text (uiout, "\nNo more reverse-execution history.\n");
+      break;
     default:
       internal_error (__FILE__, __LINE__,
 		      _("print_stop_reason: unrecognized enum value"));