Do not allow DAP clients to dereference "void *"

While investigating a different bug, I noticed that the DAP code would
report a "void *"-typed register as having children -- however,
requesting the children of this register would fail.

The issue here is that a plain "void *" can't be dereferenced.  This
patch changes the default visualizer to treat a "void *" as a scalar.

This adds a new test; but also arranges to examine all the returned
registers -- this was the first thing I attempted and it seemed
reasonable to have a test that double-checks that all the registers
really can be dereferenced as appropriate.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33228

3 files changed, 36 insertions, 10 deletions

diff --git a/gdb/python/lib/gdb/printing.py b/gdb/python/lib/gdb/printing.py
index cba27d2..cda033f 100644
--- a/gdb/python/lib/gdb/printing.py
+++ b/gdb/python/lib/gdb/printing.py
@@ -415,11 +415,17 @@ def make_visualizer(value):
             result = NoOpArrayPrinter(ty, value)
         elif ty.code in (gdb.TYPE_CODE_STRUCT, gdb.TYPE_CODE_UNION):
             result = NoOpStructPrinter(ty, value)
-        elif ty.code in (
-            gdb.TYPE_CODE_PTR,
-            gdb.TYPE_CODE_REF,
-            gdb.TYPE_CODE_RVALUE_REF,
+        elif (
+            ty.code
+            in (
+                gdb.TYPE_CODE_PTR,
+                gdb.TYPE_CODE_REF,
+                gdb.TYPE_CODE_RVALUE_REF,
+            )
+            and ty.target().code != gdb.TYPE_CODE_VOID
         ):
+            # Note we avoid "void *" here because those pointers can't
+            # be dereferenced without a cast.
             result = NoOpPointerReferencePrinter(value)
         else:
             result = NoOpScalarPrinter(value)
diff --git a/gdb/testsuite/gdb.dap/scopes.c b/gdb/testsuite/gdb.dap/scopes.c
index d8929f1..2a1d76c 100644
--- a/gdb/testsuite/gdb.dap/scopes.c
+++ b/gdb/testsuite/gdb.dap/scopes.c
@@ -27,6 +27,8 @@ int main ()
 
   static int scalar = 23;
 
+  void *ptr = (void *) &scalar;
+
   {
     const char *inner = "inner block";
 
diff --git a/gdb/testsuite/gdb.dap/scopes.exp b/gdb/testsuite/gdb.dap/scopes.exp
index 59d344b..b2066e5 100644
--- a/gdb/testsuite/gdb.dap/scopes.exp
+++ b/gdb/testsuite/gdb.dap/scopes.exp
@@ -70,7 +70,8 @@ lassign $scopes scope reg_scope
 gdb_assert {[dict get $scope name] == "Locals"} "scope is locals"
 gdb_assert {[dict get $scope presentationHint] == "locals"} \
     "locals presentation hint"
-gdb_assert {[dict get $scope namedVariables] == 3} "three vars in scope"
+set count [dict get $scope namedVariables]
+gdb_assert {$count == 4} "four vars in scope"
 
 gdb_assert {[dict get $reg_scope name] == "Registers"} \
     "second scope is registers"
@@ -89,8 +90,8 @@ set refs1 [lindex [dap_check_request_and_response "fetch variables 0,1" \
 set refs2 [lindex [dap_check_request_and_response "fetch variables 2" \
 		       "variables" \
 		       [format {o variablesReference [i %d] \
-				    start [i 2] count [i 1]} \
-			    $num]] \
+				    start [i 2] count [i %d]} \
+			    $num [expr {$count - 2}]]] \
 	       0]
 
 set vars [concat [dict get $refs1 body variables] \
@@ -115,6 +116,10 @@ foreach var $vars {
 	"scalar" {
 	    gdb_assert {[dict get $var value] == 23} "check value of scalar"
 	}
+	"ptr" {
+	    gdb_assert {[dict get $var memoryReference] != ""} \
+		"check memoryReference of ptr"
+	}
 	default {
 	    fail "unknown variable $name"
 	}
@@ -129,10 +134,23 @@ set deivals [dict get $refs body variables]
 gdb_assert {[llength $deivals] == 2} "dei has two members"
 
 set num [dict get $reg_scope variablesReference]
-# The request succeeding is sufficient.
-set val [dap_check_request_and_response "fetch first register" \
+lassign [dap_check_request_and_response "fetch all registers" \
 	     "variables" \
-	     [format {o variablesReference [i %d] count [i 1]} $num]]
+	     [format {o variablesReference [i %d] count [i %d]} $num\
+		  [dict get $reg_scope namedVariables]]] \
+    val events
+
+# If any register has children, try to fetch those as well.  This is a
+# regression test for part of PR dap/33228.
+foreach var [dict get $val body variables] {
+    set regvar [dict get $var variablesReference]
+    if {$regvar > 0} {
+	dap_check_request_and_response "fetch register children for $regvar" \
+	    "variables" \
+	    [format {o variablesReference [i %d] count [i %d]} \
+		 $regvar [dict get $var namedVariables]]
+    }
+}
 
 set num [dict get $scope variablesReference]
 set refs [lindex [dap_check_request_and_response "set variable scalar" \