[PATCH 3/3] gdb/varobj: Fix varobj_invalidate_iter

[Lancelot SIX]

The varobj_invalidate function is used meant to be called when
restarting a process, and check at this point if some of the previously
existing varobj can be recreated in the context of the new process.

Two kind of varobj are subject to re-creation:  global varobj (i.e.
varobj which reference a global variable), and floating varobj (i.e.
varobj which are always re-evaluated in the context of whatever is
the currently selected frame at the time of evaluation).

However, in the re-creation process, the varobj_invalidate_iter
recreates floating varobj as non-floating, due to an invalid parameter.
This patches fixes this and adds an assertion to check that if a varobj
is indeed recreated, it matches the original varobj "floating" property.

Another issue is that if at this recreation time the expression watched
by the floating varobj is not in scope, then the varobj is marked as
invalid.  If later the user selects a frame where the expression becomes
valid, the varobj remains invalid and this is wrong.  This patch also
make sure that floating varobj are not invalidated if they cannot be
evaluated.

The last important thing to note is that due to the previous patch, when
varobj_invalidate is executed (in the context of a new process), any
global var have already been invalidated (this has been done when the
objfile it referred to got invalidated).  As a consequence,
varobj_invalidate tries to recreate vars which are already marked as
invalid.  This does not entirely feels right, but I keep this behavior
for backward compatibility.

Tested on x86_64-linux
---
 .../gdb.mi/mi-var-invalidate-shlib.exp        | 11 ++++++++++
 gdb/varobj.c                                  | 20 ++++++++++++-------
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/gdb/testsuite/gdb.mi/mi-var-invalidate-shlib.exp b/gdb/testsuite/gdb.mi/mi-var-invalidate-shlib.exp
index 5219946d845..3ae76755309 100644
--- a/gdb/testsuite/gdb.mi/mi-var-invalidate-shlib.exp
+++ b/gdb/testsuite/gdb.mi/mi-var-invalidate-shlib.exp
@@ -77,4 +77,15 @@ with_test_prefix "in new process" {
     mi_gdb_test "-var-update floating_local" \
 	"\\^done,changelist=\\\[{name=\"floating_local\",in_scope=\"false\",type_changed=\"false\",has_more=\"0\"}\\\]" \
 	"floating_local still valid but not in scope"
+
+    # Continue inside foo
+    mi_gdb_test "299-break-insert -f -t foo" \
+	"&\"Function \\\\\"foo\\\\\" not defined.\\\\n\"\r\n299\\^done,[mi_make_breakpoint_pending -type breakpoint -disp del -pending foo]"
+    mi_send_resuming_command "exec-continue" "continue to foo"
+    mi_expect_stop "breakpoint-hit" foo ".*" ".*" "\[0-9\]+" { "" "disp=\"del\"" } "arrived at foo"
+
+    # Floating varobj is still valid, and now in scope.
+    mi_gdb_test "-var-update floating_local" \
+	"\\^done,changelist=\\\[{name=\"floating_local\",in_scope=\"true\",type_changed=\"false\",has_more=\"0\"}\\\]" \
+	"floating_local still valid and in scope"
 }
diff --git a/gdb/varobj.c b/gdb/varobj.c
index caaffe4ea70..a316f90c9e2 100644
--- a/gdb/varobj.c
+++ b/gdb/varobj.c
@@ -2360,22 +2360,28 @@ static void
 varobj_invalidate_iter (struct varobj *var)
 {
   /* global and floating var must be re-evaluated.  */
-  if (var->root->floating || var->root->valid_block == NULL)
+  if (var->root->floating || var->root->valid_block == nullptr)
     {
       struct varobj *tmp_var;
 
       /* Try to create a varobj with same expression.  If we succeed
 	 replace the old varobj, otherwise invalidate it.  */
-      tmp_var = varobj_create (NULL, var->name.c_str (), (CORE_ADDR) 0,
-			       USE_CURRENT_FRAME);
-      if (tmp_var != NULL) 
-	{ 
+      tmp_var = varobj_create (nullptr, var->name.c_str (), (CORE_ADDR) 0,
+			       var->root->floating
+			       ? USE_SELECTED_FRAME : USE_CURRENT_FRAME);
+      if (tmp_var != nullptr)
+	{
+	  gdb_assert (var->root->floating == tmp_var->root->floating);
 	  tmp_var->obj_name = var->obj_name;
 	  varobj_delete (var, 0);
 	  install_variable (tmp_var);
 	}
-      else
-	var->root->is_valid = false;
+      else if (!var->root->floating)
+	{
+	  /* Only invalidate globals as floating vars might still be valid in
+	     some other frame.  */
+	  var->root->is_valid = false;
+	}
     }
   else /* locals must be invalidated.  */
     var->root->is_valid = false;
-- 
2.25.1