Don't disable the current display in throw_exception

[Pedro Alves <pedro@codesourcery.com>]

On Thursday 04 August 2011 19:26:16, Pedro Alves wrote:
> On Wednesday 03 August 2011 20:27:10, Tom Tromey wrote:
> > Want to see something (sort of) related and gross?  From
> > throw_exception:
> > 
> >   /* Perhaps it would be cleaner to do this via the cleanup chain (not sure
> >      I can think of a reason why that is vital, though).  */
> >   if (tp != NULL)
> >     {
> >       /* Clear queued breakpoint commands.  */
> >       bpstat_clear_actions (tp->control.stop_bpstat);
> >     }
> > 
> >   disable_current_display ();
> 
> Yeah, that so needs to go away!  Any inner exception that is
> caught and handled potentially breaks breakpoints and displays...

As e.g., the display case:

(gdb) trace 2453
Tracepoint 3 at 0x40b3e9: file ../../../src/gdb/gdbserver/server.c, line 2453.
(gdb) tstart
(gdb) n
2453      int multi_mode = 0;
(gdb) n
2454      int attach = 0;
(gdb) tstop
(gdb) tfind
Found trace frame 0, tracepoint 3
#0  main (argc=<unavailable>, argv=<unavailable>) at ../../../src/gdb/gdbserver/server.c:2453
2453      int multi_mode = 0;
(gdb) display argc
Disabling display 1 to avoid infinite recursion.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1: argc = <unavailable>
(gdb) info display 
Auto-display expressions now in effect:
Num Enb Expression
1:   n  argc

An unavailable exception is thrown while evaluating
the dwarf location of argc, but that is caught by higher
layers, and shouldn't cause a disablement of the display.
Patch below fixes it, and adds a test that would
fail otherwise, for me at least, on amd64-linux.

I thought of deleting the current_display_number
global, and passing the display pointer to the cleanup,
but disable_current_display is used by infrun.c too.

Pedro Alves

2011-08-05  Pedro Alves  <pedro@codesourcery.com>

	gdb/
	* exceptions.c (throw_exception): Don't disable the current
	display.
	* printcmd.c (disable_current_display_cleanup): New function.
	(do_one_display): Install a cleanup to disable the current display
	if doing the display throws.

	gdb/testsuite/
	* gdb.trace/unavailable.exp (test_maybe_regvar_display): New procedure.
	(gdb_collect_args_test, gdb_collect_locals_test): Use it.

---
 gdb/exceptions.c                        |    1 
 gdb/printcmd.c                          |   11 ++++++++++
 gdb/testsuite/gdb.trace/unavailable.exp |   34 ++++++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

Index: src/gdb/exceptions.c
===================================================================
--- src.orig/gdb/exceptions.c	2011-08-05 15:40:32.616662949 +0100
+++ src/gdb/exceptions.c	2011-08-05 15:42:41.000000000 +0100
@@ -223,7 +223,6 @@ throw_exception (struct gdb_exception ex
       bpstat_clear_actions (tp->control.stop_bpstat);
     }
 
-  disable_current_display ();
   do_cleanups (ALL_CLEANUPS);
 
   /* Jump to the containing catch_errors() call, communicating REASON
Index: src/gdb/printcmd.c
===================================================================
--- src.orig/gdb/printcmd.c	2011-08-05 15:46:53.000000000 +0100
+++ src/gdb/printcmd.c	2011-08-05 15:47:06.636663017 +0100
@@ -1656,6 +1656,14 @@ undisplay_command (char *args, int from_
   dont_repeat ();
 }
 
+/* Cleanup that just disables the current display.  */
+
+static void
+disable_current_display_cleanup (void *arg)
+{
+  disable_current_display ();
+}
+
 /* Display a single auto-display.  
    Do nothing if the display cannot be printed in the current context,
    or if the display is disabled.  */
@@ -1663,6 +1671,7 @@ undisplay_command (char *args, int from_
 static void
 do_one_display (struct display *d)
 {
+  struct cleanup *old_chain;
   int within_current_scope;
 
   if (d->enabled_p == 0)
@@ -1715,6 +1724,7 @@ do_one_display (struct display *d)
     return;
 
   current_display_number = d->number;
+  old_chain = make_cleanup (disable_current_display_cleanup, NULL);
 
   annotate_display_begin ();
   printf_filtered ("%d", d->number);
@@ -1782,6 +1792,7 @@ do_one_display (struct display *d)
   annotate_display_end ();
 
   gdb_flush (gdb_stdout);
+  discard_cleanups (old_chain);
   current_display_number = -1;
 }
 
Index: src/gdb/testsuite/gdb.trace/unavailable.exp
===================================================================
--- src.orig/gdb/testsuite/gdb.trace/unavailable.exp	2011-08-05 15:40:32.616662949 +0100
+++ src/gdb/testsuite/gdb.trace/unavailable.exp	2011-08-05 15:42:41.596662971 +0100
@@ -103,6 +103,36 @@ proc run_trace_experiment { test_func }
 	    "tfind test frame"
 }
 
+# Test that "display VAR" works as expected, assuming VAR is wholly
+# unavailable.
+
+proc test_maybe_regvar_display { var } {
+    global gdb_prompt
+
+    # Evaluating VAR's location description may throw an internal
+    # "unavailable" exception, if for example, the value of a register
+    # necessary for computing VAR's location is unavailable.  Such an
+    # exception is caught, and should not cause automatic disablement
+    # of the current display being printed.  (GDB used to disable the
+    # current display whenever any exception was thrown.)
+    set test "display $var"
+    gdb_test_multiple "$test" "$test" {
+	-re "Disabling display ? to avoid infinite recursion.*$gdb_prompt $" {
+	    fail "$test"
+	}
+	-re "display ${var}\r\n1: ${var} = <unavailable>\r\n$gdb_prompt $" {
+	    pass "$test"
+	}
+    }
+    gdb_test "info display" ".*1:\[ \t\]+y\[ \t\]+${var}" "display ${var} is enabled"
+
+    gdb_test "undisp" \
+	"" \
+	"delete argc display" \
+	".*Delete all auto-display expressions.*y or n. $" \
+	"y"
+}
+
 #
 # Test procs
 #
@@ -171,6 +201,8 @@ proc gdb_collect_args_test {} {
     set r "${r}argarray = <unavailable>${cr}"
     gdb_test "info args" "$r" "info args"
 
+    test_maybe_regvar_display "argc"
+
     gdb_test "tfind none" \
 	"#0  end .*" \
 	"cease trace debugging"
@@ -226,6 +258,8 @@ proc gdb_collect_locals_test { func msg
     set r "${r}loci = <unavailable>${cr}"
     gdb_test "info locals" "$r" "info locals"
 
+    test_maybe_regvar_display "loci"
+
     gdb_test "tfind none" \
 	"#0  end .*" \
 	"cease trace debugging"