[RFA] Fix Cygwin problem with banned variables

["Pierre Muller" <pierre.muller@ics-cnrs.unistra.fr>]

  The problem may have two origins,
and I didn't spend time to completely analyse it,
but found a fix that seems to work.

  One problem is that while gdb_finish procedure
is never used inside testsuite '.exp' files,
gdb_init is present in lots of '.exp' files.

  But gdb_init and gdb_finsih are also called
automatically by runtest procedure
before and after sourcing the .exp file itself.
  This generates multiple calls to 'trace variable '
and only one call to 'trace remove variable '.
  But another problem is that we current implementation
uses the old way for trace insertion 'trace variable var_name w error'
and the new way for deletion 'trace remove variable var_name write error'.

  Apparently Cygwin's implementation of tcl doesn't like this
mix, and does not remove the trace.
  Uses new version 'trace add variable var_name write error'
allows the removal to work correctly.

So here is a patch that adds a global variable avoiding
multiple setting of those traces and using new
`trace add variable ' syntax.

  I checked this manually on gcc16 (as automated
tests are impossible currently due to the byte-code optimizer problem).

Is this patch OK?


Pierre Muller


2010-06-19  Pierre Muller  <muller@ics.u-strasbg.fr>

	* lib/gdb.exp (banned_variables_traced): New global variable.
	(gdb_init, gdb_finish): Use new variable to avoid multiple
	tracing.
	(gdb_init): Use `trace add variable ' instead of obsolete
	`trace variable '.

Index: src/gdb/testsuite/lib/gdb.exp
===================================================================
RCS file: /cvs/src/src/gdb/testsuite/lib/gdb.exp,v
retrieving revision 1.150
diff -u -p -r1.150 gdb.exp
--- src/gdb/testsuite/lib/gdb.exp	11 Jun 2010 21:58:20 -0000
1.150
+++ src/gdb/testsuite/lib/gdb.exp	19 Jun 2010 12:53:19 -0000
@@ -2519,6 +2519,7 @@ if ![info exists gdb_test_timeout] {
 # We try to prevent their use by monitoring write accesses and raising
 # an error when that happens.
 set banned_variables { bug_id prms_id }
+set banned_variables_traced 0
 
 proc gdb_init { args } {
     # Reset the timeout value to the default.  This way, any testcase
@@ -2530,9 +2531,13 @@ proc gdb_init { args } {
 
     # Block writes to all banned variables...
     global banned_variables
-    foreach banned_var $banned_variables {
-        global "$banned_var"
-        trace variable "$banned_var" w error
+    global banned_variables_traced
+    if (!$banned_variables_traced) {
+    	foreach banned_var $banned_variables {
+            global "$banned_var"
+            trace add variable "$banned_var" write error
+	}
+	set banned_variables_traced 1
     }
 
     return [eval default_gdb_init $args];
@@ -2552,9 +2557,13 @@ proc gdb_finish { } {
     # Unblock write access to the banned variables.  Dejagnu typically
     # resets some of them between testcases.
     global banned_variables
-    foreach banned_var $banned_variables {
-        global "$banned_var"
-        trace remove variable "$banned_var" write error
+    global banned_variables_traced
+    if ($banned_variables_traced) {
+    	foreach banned_var $banned_variables {
+            global "$banned_var"
+            trace remove variable "$banned_var" write error
+	}
+	set banned_variables_traced 0
     }
 }