Support gdbarch_convert_register_p targets in address_from_register

Since the last change to address_from_register, it no longer supports
targets that require a special conversion (gdbarch_convert_register_p)
for plain pointer type; I had assumed no target does so.

This turned out to be incorrect: MIPS64 n32 big-endian needs such a
conversion in order to properly sign-extend pointer values.

This patch fixes this regression by handling targets that need a
special conversion in address_from_register as well.

gdb/ChangeLog:

	* findvar.c (address_from_register): Handle targets requiring
	a special conversion routine even for plain pointer types.

2 files changed, 26 insertions, 4 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 2388096..8faf764 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 2014-09-10  Ulrich Weigand  <uweigand@de.ibm.com>
 
+	* findvar.c (address_from_register): Handle targets requiring
+	a special conversion routine even for plain pointer types.
+
+2014-09-10  Ulrich Weigand  <uweigand@de.ibm.com>
+
 	* rs6000-nat.c (exec_one_dummy_insn): Remove.
 	(store_register): Do not call exec_one_dummy_insn.
 
diff --git a/gdb/findvar.c b/gdb/findvar.c
index f69a8e0..cb98b86 100644
--- a/gdb/findvar.c
+++ b/gdb/findvar.c
@@ -758,11 +758,28 @@ address_from_register (int regnum, struct frame_info *frame)
      would therefore abort in get_frame_id.  However, since we only need
      a temporary value that is never used as lvalue, we actually do not
      really need to set its VALUE_FRAME_ID.  Therefore, we re-implement
-     the core of value_from_register, but use the null_frame_id.
+     the core of value_from_register, but use the null_frame_id.  */
 
-     This works only if we do not require a special conversion routine,
-     which is true for plain pointer types for all current targets.  */
-  gdb_assert (!gdbarch_convert_register_p (gdbarch, regnum, type));
+  /* Some targets require a special conversion routine even for plain
+     pointer types.  Avoid constructing a value object in those cases.  */
+  if (gdbarch_convert_register_p (gdbarch, regnum, type))
+    {
+      gdb_byte *buf = alloca (TYPE_LENGTH (type));
+      int optim, unavail, ok;
+
+      ok = gdbarch_register_to_value (gdbarch, frame, regnum, type,
+				      buf, &optim, &unavail);
+      if (!ok)
+	{
+	  /* This function is used while computing a location expression.
+	     Complain about the value being optimized out, rather than
+	     letting value_as_address complain about some random register
+	     the expression depends on not being saved.  */
+	  error_value_optimized_out ();
+	}
+
+      return unpack_long (type, buf);
+    }
 
   value = gdbarch_value_from_register (gdbarch, type, regnum, null_frame_id);
   read_frame_register_value (value, frame);