[RFA] Reverse Debugging, 4/5

Michael Snyder
2008-10-01T19:21:02Z

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This patch (#4), adds special handling for the "finish" command
when executing in reverse. The new code can't actually be
invoked until patch #5 is added, and so has no user visible
effect.

Tested under RHEL native with no change in results.

2008-09-30 Michael Snyder <msnyder@vmware.com>

* breakpoint.h (breakpoint_silence): Export.
* breakpoint.c (breakpoint_silence): New function.
* infcmd.c (finish_command): Check for reverse exec direction.
(finish_backward): New function, handle finish cmd in reverse.

Index: breakpoint.c
===================================================================
RCS file: /cvs/src/src/gdb/breakpoint.c,v
retrieving revision 1.352
diff -u -p -r1.352 breakpoint.c
--- breakpoint.c 16 Sep 2008 18:55:01 -0000 1.352
+++ breakpoint.c 30 Sep 2008 23:53:41 -0000
@@ -7741,6 +7741,13 @@ breakpoint_clear_ignore_counts (void)
b->ignore_count = 0;
}

+void
+breakpoint_silence (struct breakpoint *b)
+{
+ /* Silence the breakpoint. */
+ b->silent = 1;
+}
+
/* Command to set ignore-count of breakpoint N to COUNT. */

static void
Index: breakpoint.h
===================================================================
RCS file: /cvs/src/src/gdb/breakpoint.h,v
retrieving revision 1.79
diff -u -p -r1.79 breakpoint.h
--- breakpoint.h 22 Sep 2008 15:26:53 -0000 1.79
+++ breakpoint.h 30 Sep 2008 23:53:41 -0000
@@ -884,4 +884,7 @@ extern int breakpoints_always_inserted_m
in our opinion won't ever trigger. */
extern void breakpoint_retire_moribund (void);

+/* Tell a breakpoint to be quiet. */
+extern void breakpoint_silence (struct breakpoint *);
+
#endif /* !defined (BREAKPOINT_H) */
Index: infcmd.c
===================================================================
RCS file: /cvs/src/src/gdb/infcmd.c,v
retrieving revision 1.212
diff -u -p -r1.212 infcmd.c
--- infcmd.c 22 Sep 2008 15:20:08 -0000 1.212
+++ infcmd.c 30 Sep 2008 23:53:41 -0000
@@ -1369,6 +1369,8 @@ finish_command_continuation_free_arg (vo
/* "finish": Set a temporary breakpoint at the place the selected
frame will return to, then continue. */

+static void finish_backwards (struct symbol *, struct thread_info *);
+
static void
finish_command (char *arg, int from_tty)
{
@@ -1412,13 +1414,6 @@ finish_command (char *arg, int from_tty)

clear_proceed_status ();

- sal = find_pc_line (get_frame_pc (frame), 0);
- sal.pc = get_frame_pc (frame);
-
- breakpoint = set_momentary_breakpoint (sal, get_frame_id (frame), bp_finish);
-
- old_chain = make_cleanup_delete_breakpoint (breakpoint);
-
/* Find the function we will return from. */

function = find_pc_function (get_frame_pc (get_selected_frame (NULL)));
@@ -1427,10 +1422,29 @@ finish_command (char *arg, int from_tty)
source. */
if (from_tty)
{
- printf_filtered (_("Run till exit from "));
+ if (target_get_execution_direction () == EXEC_REVERSE)
+ printf_filtered ("Run back to call of ");
+ else
+ printf_filtered ("Run till exit from ");
+
print_stack_frame (get_selected_frame (NULL), 1, LOCATION);
}

+ if (target_get_execution_direction () == EXEC_REVERSE)
+ {
+ /* Split off at this point. */
+ finish_backwards (function, tp);
+ return;
+ }
+
+ sal = find_pc_line (get_frame_pc (frame), 0);
+ sal.pc = get_frame_pc (frame);
+
+ breakpoint = set_momentary_breakpoint (sal, get_frame_id (frame),
+ bp_finish);
+
+ old_chain = make_cleanup_delete_breakpoint (breakpoint);
+
tp->proceed_to_finish = 1; /* We want stop_registers, please... */
make_cleanup_restore_integer (&suppress_stop_observer);
suppress_stop_observer = 1;
@@ -1514,6 +1528,66 @@ It stopped at a breakpoint that has sinc
Type \"info stack\" or \"info registers\" for more information.\n"));
}
}
+
+static void
+finish_backwards (struct symbol *function, struct thread_info *tp)
+{
+ struct symtab_and_line sal;
+ struct breakpoint *breakpoint;
+ struct cleanup *old_chain;
+ CORE_ADDR func_addr;
+ int back_up;
+
+ if (find_pc_partial_function (get_frame_pc (get_current_frame ()),
+ NULL, &func_addr, NULL) == 0)
+ internal_error (__FILE__, __LINE__,
+ "Finish: couldn't find function.");
+
+ sal = find_pc_line (func_addr, 0);
+
+ /* TODO: Let's not worry about async until later. */
+
+ /* We don't need a return value. */
+ tp->proceed_to_finish = 0;
+ /* Special case: if we're sitting at the function entry point,
+ then all we need to do is take a reverse singlestep. We
+ don't need to set a breakpoint, and indeed it would do us
+ no good to do so.
+
+ Note that this can only happen at frame #0, since there's
+ no way that a function up the stack can have a return address
+ that's equal to its entry point. */
+
+ if (sal.pc != read_pc ())
+ {
+ /* Set breakpoint and continue. */
+ breakpoint =
+ set_momentary_breakpoint (sal,
+ get_frame_id (get_selected_frame (NULL)),
+ bp_breakpoint);
+ /* Tell the breakpoint to keep quiet. We won't be done
+ until we've done another reverse single-step. */
+ breakpoint_silence (breakpoint);
+ old_chain = make_cleanup_delete_breakpoint (breakpoint);
+ proceed ((CORE_ADDR) -1, TARGET_SIGNAL_DEFAULT, 0);
+ /* We will be stopped when proceed returns. */
+ back_up = bpstat_find_breakpoint (tp->stop_bpstat, breakpoint) != NULL;
+ do_cleanups (old_chain);
+ }
+ else
+ back_up = 1;
+ if (back_up)
+ {
+ /* If in fact we hit the step-resume breakpoint (and not
+ some other breakpoint), then we're almost there --
+ we just need to back up by one more single-step. */
+ /* (Kludgy way of letting wait_for_inferior know...) */
+ tp->step_range_start = tp->step_range_end = 1;
+ proceed ((CORE_ADDR) -1, TARGET_SIGNAL_DEFAULT, 1);
+ }
+ return;
+}
+
\f
static void
environment_info (char *var, int from_tty)