Re: [RFA] Fix hw watchpoints in process record.

[Hui Zhu <teawater@gmail.com>]

Still not very well, with the old program:

(gdb) start
Temporary breakpoint 1 at 0x80483c1: file 1.c, line 20.
Starting program: /home/teawater/gdb/a.out
warning: the debug information found in "/lib/ld-2.7.so" does not
match "/lib/ld-linux.so.2" (CRC mismatch).

warning: the debug information found in
"/lib/tls/i686/cmov/libc-2.7.so" does not match
"/lib/tls/i686/cmov/libc.so.6" (CRC mismatch).


Temporary breakpoint 1, main () at 1.c:20
20	       int     b = 0;
(gdb) record
(gdb) n
During symbol reading, incomplete CFI data; unspecified registers
(e.g., eax) at 0x80483be.
21	       int     c = 1;
(gdb)
24		printf ("a = %d b = %d c = %d\n", a, b, c);
(gdb) hw
Undefined command: "hw".  Try "help".
(gdb) hb
Hardware assisted breakpoint 2 at 0x80483cf: file 1.c, line 24.
(gdb) c
Continuing.
a = 0 b = 0 c = 1
a = 3
a = 3 b = 3 c = 1
a = 3 b = 3 c = 2
a = 1 b = 3 c = 2
The next instruction is syscall exit_group.  It will make the program
exit.  Do you want to stop the program?([y] or n)
Process record: inferior program stopped.

Program received signal SIGTRAP, Trace/breakpoint trap.
0xb7fe3405 in __kernel_vsyscall ()
(gdb) rc
Continuing.

Breakpoint 2, main () at 1.c:24
24		printf ("a = %d b = %d c = %d\n", a, b, c);
(gdb) rc
Continuing.

No more reverse-execution history.
main () at 1.c:20
20	       int     b = 0;
(gdb) c
Continuing.

Program received signal SIGTRAP, Trace/breakpoint trap.
0x080483d0 in main () at 1.c:24
24		printf ("a = %d b = %d c = %d\n", a, b, c);
(gdb) c
Continuing.

No more reverse-execution history.
0xb7fe3405 in __kernel_vsyscall ()
(gdb) rc
Continuing.

No more reverse-execution history.
main () at 1.c:20
20	       int     b = 0;
(gdb) c
Continuing.

No more reverse-execution history.
0xb7fe3405 in __kernel_vsyscall ()
(gdb) rc
Continuing.

No more reverse-execution history.
main () at 1.c:20
20	       int     b = 0;
(gdb) info b
Num     Type           Disp Enb Address    What
2       hw breakpoint  keep y   0x080483cf in main at 1.c:24
	breakpoint already hit 1 time
(gdb) c
Continuing.

No more reverse-execution history.
0xb7fe3405 in __kernel_vsyscall ()


Thanks,
Hui

On Fri, Nov 6, 2009 at 02:40, Michael Snyder <msnyder@vmware.com> wrote:
> Hui Zhu wrote:
>>
>> Hi Michael,
>>
>> I do some test with this patch.  But sometime hb didn't work in replay
>> mode.
>
> OK, thanks, I see the problem.
>
> Try this patch instead.
>
>
> 2009-10-31  Michael Snyder  <msnyder@vmware.com>
>        Make hardware watchpoints work for process record.
>        * breakpoint.c (watchpoint_check_1): Abstracted from
> watchpoint_check.
>        (watchpoint_check_2): Check_error entry point for above.
>        (watchpoint_check): Call watchpoint_check_1.
>        (hw_watchpoint_check): New function.  Return true if
>        a hardware watchpoint expression has changed.
>        * breakpoint.h (hw_watchpoint_check): Export.
>
>        * record.c (record_beneath_to_stopped_by_watchpoint): New pointer.
>        (record_open): Initialize above pointer.
>        (record_stopped_by_watchpoint): New target method.
>        (record_wait): Check to see if hitting hardware watchpoint.
>
> Index: gdb/breakpoint.c
> ===================================================================
> --- gdb.orig/breakpoint.c       2009-11-05 09:54:36.000000000 -0800
> +++ gdb/breakpoint.c    2009-11-05 10:19:07.000000000 -0800
> @@ -3075,18 +3075,13 @@
>  #define BP_TEMPFLAG 1
>  #define BP_HARDWAREFLAG 2
>
> -/* Check watchpoint condition.  */
> -
>  static int
> -watchpoint_check (void *p)
> +watchpoint_check_1 (void *p, struct value **new_valp)
>  {
> -  bpstat bs = (bpstat) p;
> -  struct breakpoint *b;
> +  struct breakpoint *b = p;
>   struct frame_info *fr;
>   int within_current_scope;
>
> -  b = bs->breakpoint_at->owner;
> -
>   if (b->exp_valid_block == NULL)
>     within_current_scope = 1;
>   else
> @@ -3137,20 +3132,16 @@
>          we might be in the middle of evaluating a function call.  */
>
>       struct value *mark = value_mark ();
> -      struct value *new_val;
>
> -      fetch_watchpoint_value (b->exp, &new_val, NULL, NULL);
> -      if ((b->val != NULL) != (new_val != NULL)
> -         || (b->val != NULL && !value_equal (b->val, new_val)))
> +      fetch_watchpoint_value (b->exp, new_valp, NULL, NULL);
> +      if ((b->val != NULL) != (*new_valp != NULL)
> +         || (b->val != NULL && !value_equal (b->val, *new_valp)))
>        {
> -         if (new_val != NULL)
> +         if (*new_valp != NULL)
>            {
> -             release_value (new_val);
> +             release_value (*new_valp);
>              value_free_to_mark (mark);
>            }
> -         bs->old_val = b->val;
> -         b->val = new_val;
> -         b->val_valid = 1;
>          /* We will stop here */
>          return WP_VALUE_CHANGED;
>        }
> @@ -3181,8 +3172,9 @@
>          (uiout, "reason", async_reason_lookup
> (EXEC_ASYNC_WATCHPOINT_SCOPE));
>       ui_out_text (uiout, "\nWatchpoint ");
>       ui_out_field_int (uiout, "wpnum", b->number);
> -      ui_out_text (uiout, " deleted because the program has left the block
> in\n\
> -which its expression is valid.\n");
> +      ui_out_text (uiout,
> +                  " deleted because the program has left the block in\n\
> +which its expression is valid.\n");
>
>       if (b->related_breakpoint)
>        b->related_breakpoint->disposition = disp_del_at_next_stop;
> @@ -3192,6 +3184,36 @@
>     }
>  }
>
> +static int
> +watchpoint_check_2 (void *p)
> +{
> +  struct value *notused;
> +
> +  return watchpoint_check_1 (p, &notused);
> +}
> +
> +/* Check watchpoint condition.  */
> +
> +static int
> +watchpoint_check (void *p)
> +{
> +  bpstat bs = (bpstat) p;
> +  struct value *new_val;
> +  struct breakpoint *b;
> +  int ret;
> +
> +  b = bs->breakpoint_at->owner;
> +  ret = watchpoint_check_1 (b, &new_val);
> +
> +  if (ret == WP_VALUE_CHANGED)
> +    {
> +      bs->old_val = b->val;
> +      b->val = new_val;
> +      b->val_valid = 1;
> +    }
> +  return ret;
> +}
> +
>  /* Return true if it looks like target has stopped due to hitting
>    breakpoint location BL.  This function does not check if we
>    should stop, only if BL explains the stop.   */
> @@ -3250,6 +3272,29 @@
>   return 1;
>  }
>
> +int
> +hw_watchpoint_check (void)
> +{
> +  struct breakpoint *b;
> +  struct value *new_val;
> +
> +  ALL_BREAKPOINTS (b)
> +    if (b->type == bp_hardware_watchpoint
> +       || b->type == bp_access_watchpoint)
> +      {
> +       char *msg
> +         = xstrprintf (_("Error evaluating expression for watchpoint
> %d\n"),
> +                       b->number);
> +       struct cleanup *cleanups = make_cleanup (xfree, msg);
> +       int e = catch_errors (watchpoint_check_2, b, msg, RETURN_MASK_ALL);
> +       do_cleanups (cleanups);
> +       if (e == WP_VALUE_CHANGED)
> +         return 1;     /* should stop */
> +      }
> +  return 0;            /* don't stop */
> +}
> +
> +
>  /* If BS refers to a watchpoint, determine if the watched values
>    has actually changed, and we should stop.  If not, set BS->stop
>    to 0.  */
> @@ -3267,7 +3312,7 @@
>       CORE_ADDR addr;
>       struct value *v;
>       int must_check_value = 0;
> -
> +
>       if (b->type == bp_watchpoint)
>        /* For a software watchpoint, we must always check the
>           watched value.  */
> @@ -3284,7 +3329,7 @@
>           value.  Access and read watchpoints are out of luck; without
>           a data address, we can't figure it out.  */
>        must_check_value = 1;
> -
> +
>       if (must_check_value)
>        {
>          char *message = xstrprintf ("Error evaluating expression for
> watchpoint %d\n",
> Index: gdb/breakpoint.h
> ===================================================================
> --- gdb.orig/breakpoint.h       2009-11-05 09:54:36.000000000 -0800
> +++ gdb/breakpoint.h    2009-11-05 10:13:18.000000000 -0800
> @@ -978,4 +978,6 @@
>    is newly allocated; the caller should free when done with it.  */
>  extern VEC(breakpoint_p) *all_tracepoints (void);
>
> +extern int hw_watchpoint_check (void);
> +
>  #endif /* !defined (BREAKPOINT_H) */
> Index: gdb/record.c
> ===================================================================
> --- gdb.orig/record.c   2009-11-05 09:54:36.000000000 -0800
> +++ gdb/record.c        2009-11-05 10:24:30.000000000 -0800
> @@ -224,6 +224,7 @@
>                                                   struct bp_target_info *);
>  static int (*record_beneath_to_remove_breakpoint) (struct gdbarch *,
>                                                   struct bp_target_info *);
> +static int (*record_beneath_to_stopped_by_watchpoint) (void);
>
>  /* Alloc and free functions for record_reg, record_mem, and record_end
>    entries.  */
> @@ -770,6 +771,7 @@
>                                        struct bp_target_info *);
>  static int (*tmp_to_remove_breakpoint) (struct gdbarch *,
>                                        struct bp_target_info *);
> +static int (*tmp_to_stopped_by_watchpoint) (void);
>
>  static void record_restore (void);
>
> @@ -894,6 +896,8 @@
>        tmp_to_insert_breakpoint = t->to_insert_breakpoint;
>       if (!tmp_to_remove_breakpoint)
>        tmp_to_remove_breakpoint = t->to_remove_breakpoint;
> +      if (!tmp_to_stopped_by_watchpoint)
> +       tmp_to_stopped_by_watchpoint = t->to_stopped_by_watchpoint;
>     }
>   if (!tmp_to_xfer_partial)
>     error (_("Could not find 'to_xfer_partial' method on the target
> stack."));
> @@ -915,6 +919,7 @@
>   record_beneath_to_xfer_partial = tmp_to_xfer_partial;
>   record_beneath_to_insert_breakpoint = tmp_to_insert_breakpoint;
>   record_beneath_to_remove_breakpoint = tmp_to_remove_breakpoint;
> +  record_beneath_to_stopped_by_watchpoint = tmp_to_stopped_by_watchpoint;
>
>   if (current_target.to_stratum == core_stratum)
>     record_core_open_1 (name, from_tty);
> @@ -1010,6 +1015,9 @@
>     record_list = record_list->prev;
>  }
>
> +/* Flag set to TRUE for target_stopped_by_watchpoint.  */
> +static int record_hw_watchpoint = 0;
> +
>  /* "to_wait" target method for process record target.
>
>    In record mode, the target is always run in singlestep mode
> @@ -1069,21 +1077,27 @@
>                {
>                  struct regcache *regcache;
>
> -                 /* Yes -- check if there is a breakpoint.  */
> +                 /* Yes -- check if there is a breakpoint or watchpoint.
>  */
>                  registers_changed ();
>                  regcache = get_current_regcache ();
>                  tmp_pc = regcache_read_pc (regcache);
>                  if (breakpoint_inserted_here_p (get_regcache_aspace
> (regcache),
> -                                                 tmp_pc))
> +                                                 tmp_pc)
> +                     || target_stopped_by_watchpoint ())
>                    {
> -                     /* There is a breakpoint.  GDB will want to stop.  */
> -                     struct gdbarch *gdbarch = get_regcache_arch
> (regcache);
> +                     /* There is a breakpoint, or watchpoint.
> +                        GDB will want to stop.  */
> +                     if (!target_stopped_by_watchpoint ())
> +                       {
> +                         struct gdbarch *gdbarch
> +                           = get_regcache_arch (regcache);
>                      CORE_ADDR decr_pc_after_break
>                        = gdbarch_decr_pc_after_break (gdbarch);
>                      if (decr_pc_after_break)
>                        regcache_write_pc (regcache,
>                                           tmp_pc + decr_pc_after_break);
>                    }
> +                   }
>                  else
>                    {
>                      /* There is not a breakpoint, and gdb is not
> @@ -1116,9 +1130,10 @@
>       struct cleanup *old_cleanups = make_cleanup (record_wait_cleanups, 0);
>       CORE_ADDR tmp_pc;
>
> +      record_hw_watchpoint = 0;
>       status->kind = TARGET_WAITKIND_STOPPED;
>
> -      /* Check breakpoint when forward execute.  */
> +      /* Check for breakpoint or watchpoint when forward execute.  */
>       if (execution_direction == EXEC_FORWARD)
>        {
>          tmp_pc = regcache_read_pc (regcache);
> @@ -1136,6 +1151,15 @@
>                                   gdbarch_decr_pc_after_break (gdbarch));
>              goto replay_out;
>            }
> +         set_executing (inferior_ptid, 0);
> +         if (hw_watchpoint_check ())
> +           {
> +             if (record_debug)
> +               fprintf_unfiltered (gdb_stdlog,
> +                                   "Process record: hit hw watchpoint.\n");
> +             record_hw_watchpoint = 1;
> +           }
> +
>        }
>
>       record_get_sig = 0;
> @@ -1155,6 +1179,7 @@
>         stop.  */
>       do
>        {
> +         set_executing (inferior_ptid, 0);
>          /* Check for beginning and end of log.  */
>          if (execution_direction == EXEC_REVERSE
>              && record_list == &record_first)
> @@ -1219,6 +1244,15 @@
>                                           gdbarch_decr_pc_after_break
> (gdbarch));
>                      continue_flag = 0;
>                    }
> +                 /* check watchpoint */
> +                 if (hw_watchpoint_check ())
> +                   {
> +                     if (record_debug)
> +                       fprintf_unfiltered (gdb_stdlog,
> +                                           "Process record: hit hw
> watchpoint.\n");
> +                     record_hw_watchpoint = 1;
> +                     continue_flag = 0;
> +                   }
>                  /* Check target signal */
>                  if (record_list->u.end.sigval != TARGET_SIGNAL_0)
>                    /* FIXME: better way to check */
> @@ -1238,6 +1272,7 @@
>                  if (record_list->next)
>                    record_list = record_list->next;
>                }
> +             set_executing (inferior_ptid, 1);
>            }
>        }
>       while (continue_flag);
> @@ -1260,6 +1295,16 @@
>   return inferior_ptid;
>  }
>
> +/* to_stopped_by_watchpoint method */
> +static int
> +record_stopped_by_watchpoint (void)
> +{
> +  if (RECORD_IS_REPLAY)
> +    return record_hw_watchpoint;
> +  else
> +    return record_beneath_to_stopped_by_watchpoint ();
> +}
> +
>  /* "to_disconnect" method for process record target.  */
>
>  static void
> @@ -1599,6 +1644,7 @@
>   /* Add bookmark target methods.  */
>   record_ops.to_get_bookmark = record_get_bookmark;
>   record_ops.to_goto_bookmark = record_goto_bookmark;
> +  record_ops.to_stopped_by_watchpoint = record_stopped_by_watchpoint;
>   record_ops.to_magic = OPS_MAGIC;
>  }
>
> @@ -1807,6 +1853,7 @@
>   /* Add bookmark target methods.  */
>   record_core_ops.to_get_bookmark = record_get_bookmark;
>   record_core_ops.to_goto_bookmark = record_goto_bookmark;
> +  record_core_ops.to_stopped_by_watchpoint = record_stopped_by_watchpoint;
>   record_core_ops.to_magic = OPS_MAGIC;
>  }
>
> Index: gdb/NEWS
> ===================================================================
> --- gdb.orig/NEWS       2009-11-05 09:54:36.000000000 -0800
> +++ gdb/NEWS    2009-11-05 10:13:18.000000000 -0800
> @@ -88,6 +88,10 @@
>   creates a new one.  This is useful to be able to restart the old
>   executable after the inferior having done an exec call.
>
> +* Bug fixes
> +
> +Process record now works correctly with hardware watchpoints.
> +
>  *** Changes in GDB 7.0
>
>  * GDB now has an interface for JIT compilation.  Applications that
> Index: gdb/testsuite/gdb.reverse/watch-reverse.exp
> ===================================================================
> --- gdb.orig/testsuite/gdb.reverse/watch-reverse.exp    2009-11-05
> 09:54:36.000000000 -0800
> +++ gdb/testsuite/gdb.reverse/watch-reverse.exp 2009-11-05
> 10:13:18.000000000 -0800
> @@ -38,8 +38,8 @@
>     # FIXME: command ought to acknowledge, so we can test if it succeeded.
>  }
>
> -# Only software watchpoints can be used in reverse
> -gdb_test "set can-use-hw-watchpoints 0" "" ""
> +# Test software watchpoints
> +gdb_test "set can-use-hw-watchpoints 0" "" "disable hw watchpoints"
>
>  gdb_test "break marker1" \
>     "Breakpoint $decimal at $hex: file .*$srcfile, line $decimal.*" \
> @@ -122,3 +122,81 @@
>  gdb_test "continue" \
>     ".*\[Ww\]atchpoint.*ival3.*Old value = 0.*New value = -1.*ival3 = count;
> ival4 = count;.*" \
>     "watchpoint hit in reverse, fifth time"
> +
> +gdb_test "set can-use-hw-watchpoints 1" "" "enable hw watchpoints"
> +
> +###
> +###
> +###
> +
> +# FIXME 'set exec-dir' command should give some output so we can test.
> +gdb_test "set exec-direction forward" "" "set forward"
> +
> +# Continue until first change, from -1 to 0
> +
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = -1.*New value = 0.*ival3 =
> count; ival4 = count;.*" \
> +    "watchpoint hit, forward replay, first time"
> +
> +# Continue until the next change, from 0 to 1.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 0.*New value = 1.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit, forward replay, second time"
> +
> +# Continue until the next change, from 1 to 2.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 1.*New value = 2.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit, forward replay, third time"
> +
> +# Continue until the next change, from 2 to 3.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 2.*New value = 3.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit, forward replay, fourth time"
> +
> +# Continue until the next change, from 3 to 4.
> +# Note that this one is outside the loop.
> +
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 3.*New value = 4.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit, forward replay, fifth time"
> +
> +# Continue until we hit the finishing marker function.
> +# Make sure we hit no more watchpoints.
> +
> +gdb_test "continue" "marker2 .*" "replay forward to marker2"
> +
> +###
> +###
> +###
> +
> +# FIXME 'set exec-dir' command should give some output so we can test.
> +gdb_test "set exec-direction reverse" "" "set reverse"
> +
> +# Reverse until the previous change, from 4 to 3
> +# Note that this one is outside the loop
> +
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 4.*New value = 3.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, first time"
> +
> +# Reverse until the previous change, from 3 to 2.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 3.*New value = 2.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, second time"
> +
> +# Reverse until the previous change, from 2 to 1.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 2.*New value = 1.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, third time"
> +
> +# Reverse until the previous change, from 1 to 0.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 1.*New value = 0.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, fourth time"
> +
> +# Reverse until first change, from 0 to -1
> +
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 0.*New value = -1.*ival3 =
> count; ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, fifth time"
> +
> Index: gdb/testsuite/gdb.reverse/watch-precsave.exp
> ===================================================================
> --- gdb.orig/testsuite/gdb.reverse/watch-precsave.exp   2009-11-05
> 09:54:36.000000000 -0800
> +++ gdb/testsuite/gdb.reverse/watch-precsave.exp        2009-11-05
> 10:13:18.000000000 -0800
> @@ -1,4 +1,4 @@
> -# Copyright 2008, 2009 Free Software Foundation, Inc.
> +# Copyright 2009 Free Software Foundation, Inc.
>
>  # This program is free software; you can redistribute it and/or modify
>  # it under the terms of the GNU General Public License as published by
> @@ -140,3 +140,81 @@
>  gdb_test "continue" \
>     ".*\[Ww\]atchpoint.*ival3.*Old value = 0.*New value = -1.*ival3 = count;
> ival4 = count;.*" \
>     "watchpoint hit in reverse, fifth time"
> +
> +gdb_test "set can-use-hw-watchpoints 1" "" "enable hw watchpoints"
> +
> +###
> +###
> +###
> +
> +# FIXME 'set exec-dir' command should give some output so we can test.
> +gdb_test "set exec-direction forward" "" "set forward"
> +
> +# Continue until first change, from -1 to 0
> +
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = -1.*New value = 0.*ival3 =
> count; ival4 = count;.*" \
> +    "watchpoint hit, forward replay, first time"
> +
> +# Continue until the next change, from 0 to 1.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 0.*New value = 1.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit, forward replay, second time"
> +
> +# Continue until the next change, from 1 to 2.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 1.*New value = 2.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit, forward replay, third time"
> +
> +# Continue until the next change, from 2 to 3.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 2.*New value = 3.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit, forward replay, fourth time"
> +
> +# Continue until the next change, from 3 to 4.
> +# Note that this one is outside the loop.
> +
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 3.*New value = 4.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit, forward replay, fifth time"
> +
> +# Continue until we hit the finishing marker function.
> +# Make sure we hit no more watchpoints.
> +
> +gdb_test "continue" "marker2 .*" "replay forward to marker2"
> +
> +###
> +###
> +###
> +
> +# FIXME 'set exec-dir' command should give some output so we can test.
> +gdb_test "set exec-direction reverse" "" "set reverse"
> +
> +# Reverse until the previous change, from 4 to 3
> +# Note that this one is outside the loop
> +
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 4.*New value = 3.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, first time"
> +
> +# Reverse until the previous change, from 3 to 2.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 3.*New value = 2.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, second time"
> +
> +# Reverse until the previous change, from 2 to 1.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 2.*New value = 1.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, third time"
> +
> +# Reverse until the previous change, from 1 to 0.
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 1.*New value = 0.*ival3 = count;
> ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, fourth time"
> +
> +# Reverse until first change, from 0 to -1
> +
> +gdb_test "continue" \
> +    ".*\[Ww\]atchpoint.*ival3.*Old value = 0.*New value = -1.*ival3 =
> count; ival4 = count;.*" \
> +    "watchpoint hit in reverse, HW, fifth time"
> +
>
>