[commit] Fix struct and struct-pointer casts

[Daniel Jacobowitz <drow at false dot org>]

This is a fix related to Aleksandar's patch from April.  It's been
bugging me for a while but I only today tracked it down.

value_cast_structs returned its argument if the cast failed.  The
argument, of course, was of the uncasted type.  So one symptom of
the bug was "print (struct One) two" returning a value of type Two.
This only shows up in C++, where TYPE_NAME is set on structs.

The more insidious problem was that value_cast_pointers does not
change the enclosing type if value_cast_structs succeeds - that's a
feature, and an oversight when we broke the code out into a separate
function.  So you'd end up with pointers where the enclosing type was
unchanged but the type was changed.  value_fetch_lazy reads bytes the
size of the enclosing type.  So we could read fewer bytes than
necessary, and print garbage for the rest.

This turned up a related bug; the lack of check_typedef in
value_fetch_lazy meant that sometimes we'd read no bytes at all.

Tested on x86_64 and checked in.

-- 
Daniel Jacobowitz
CodeSourcery

2008-09-08  Daniel Jacobowitz  <dan@codesourcery.com>

	* valops.c (value_cast_structs): Return NULL for failure.
	(value_cast): Handle NULL from value_cast_structs.
	(value_fetch_lazy): Call check_typedef.  Remove unused variable.

	* gdb.base/structs3.c, gdb.base/structs3.exp: New files.

Index: valops.c
===================================================================
RCS file: /cvs/src/src/gdb/valops.c,v
retrieving revision 1.194
diff -u -p -r1.194 valops.c
--- valops.c	21 Aug 2008 20:13:08 -0000	1.194
+++ valops.c	8 Sep 2008 22:12:34 -0000
@@ -193,7 +193,8 @@ allocate_space_in_inferior (int len)
 
 /* Cast struct value VAL to type TYPE and return as a value.
    Both type and val must be of TYPE_CODE_STRUCT or TYPE_CODE_UNION
-   for this to work. Typedef to one of the codes is permitted.  */
+   for this to work.  Typedef to one of the codes is permitted.
+   Returns NULL if the cast is neither an upcast nor a downcast.  */
 
 static struct value *
 value_cast_structs (struct type *type, struct value *v2)
@@ -244,7 +245,8 @@ value_cast_structs (struct type *type, s
 	  return value_at (type, addr2);
 	}
     }
-  return v2;
+
+  return NULL;
 }
 
 /* Cast one pointer or reference type to another.  Both TYPE and
@@ -397,7 +399,12 @@ value_cast (struct type *type, struct va
   if ((code1 == TYPE_CODE_STRUCT || code1 == TYPE_CODE_UNION)
       && (code2 == TYPE_CODE_STRUCT || code2 == TYPE_CODE_UNION)
       && TYPE_NAME (type) != 0)
-    return value_cast_structs (type, arg2);
+    {
+      struct value *v = value_cast_structs (type, arg2);
+      if (v)
+	return v;
+    }
+
   if (code1 == TYPE_CODE_FLT && scalar)
     return value_from_double (type, value_as_double (arg2));
   else if (code1 == TYPE_CODE_DECFLOAT && scalar)
@@ -615,9 +622,8 @@ value_fetch_lazy (struct value *val)
   if (VALUE_LVAL (val) == lval_memory)
     {
       CORE_ADDR addr = VALUE_ADDRESS (val) + value_offset (val);
-      int length = TYPE_LENGTH (value_enclosing_type (val));
+      int length = TYPE_LENGTH (check_typedef (value_enclosing_type (val)));
 
-      struct type *type = value_type (val);
       if (length)
 	read_memory (addr, value_contents_all_raw (val), length);
     }
Index: testsuite/gdb.base/structs3.c
===================================================================
RCS file: testsuite/gdb.base/structs3.c
diff -N testsuite/gdb.base/structs3.c
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/structs3.c	8 Sep 2008 22:12:34 -0000
@@ -0,0 +1,42 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2008
+   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
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+struct One
+{
+  int x;
+};
+
+struct Two
+{
+  struct One one;
+  int x, y;
+};
+
+struct Two two = { { 1 }, 2, 3 };
+
+typedef struct One tOne;
+typedef struct Two tTwo;
+
+tOne *onep = &two.one;
+tTwo *twop = &two;
+
+int main()
+{
+  onep->x = twop->y;
+  return 0;
+}
Index: testsuite/gdb.base/structs3.exp
===================================================================
RCS file: testsuite/gdb.base/structs3.exp
diff -N testsuite/gdb.base/structs3.exp
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/structs3.exp	8 Sep 2008 22:12:34 -0000
@@ -0,0 +1,37 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2008 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
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+set testfile "structs3"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+
+if { [prepare_for_testing structs3.exp "structs3" "" {debug}] } {
+    return -1
+}
+
+set vhn "\\$\[0-9\]+"
+
+# Check the real contents.
+gdb_test "print two" "$vhn = {one = {x = 1}, x = 2, y = 3}"
+
+# Check through the pointer.
+gdb_test "print *twop" "$vhn = {one = {x = 1}, x = 2, y = 3}"
+
+# Check through a pointer to a smaller type, casted up.
+gdb_test "print *(struct Two *)onep" "$vhn = {one = {x = 1}, x = 2, y = 3}"
+
+gdb_test "print *(tTwo *)onep" "$vhn = {one = {x = 1}, x = 2, y = 3}"