Re: [PATCH] Assert on lval_register

[Yao Qi <qiyaoltc at gmail dot com>]

On 16-11-30 22:16:37, Ulrich Weigand wrote:
 
> > This also reveals a design issue in frame_register_unwind, that is
> > arguments addrp and realnump are mutually exclusive, we either use
> > addrp (for lval_memory), or use realnump (for lval_register).  This
> > can be done in a separate patch.
> 
> I think we should simply get rid of frame_register_unwind.  Callers
> should be changed to use frame_unwind_register_value directly, and
> just operate on the value.
> 

Yeah, that is what I was trying to do, but we should be careful on
the value management in the end of frame_register_unwind,

  /* Dispose of the new value.  This prevents watchpoints from
     trying to watch the saved frame pointer.  */
  release_value (value);
  value_free (value);

> >    *lvalp = VALUE_LVAL (value);
> >    *addrp = value_address (value);
> > -  *realnump = VALUE_REGNUM (value);
> > +  if (*lvalp == lval_register)
> > +    *realnump = VALUE_REGNUM (value);
> 
> But as long as the above change is not done yet, maybe we ought to
> at least provide a defined value (e.g. -1), to avoid callers maybe
> making use of uninitialized variables?
> 

OK, how about the patch below?

-- 
Yao (齐尧)

>From 581e1b80ea631d5bcfb5fc64b07a36fd71f5d55e Mon Sep 17 00:00:00 2001
From: Yao Qi <yao.qi@linaro.org>
Date: Thu, 24 Nov 2016 09:08:00 +0000
Subject: [PATCH] Assert on lval_register

This patch adds asserts where the value's lval must be lval_register.
This triggers an error in frame_register_unwind because VALUE_REGNUM
is used but value's lval is not lval_register.

This also reveals a design issue in frame_register_unwind, that is
arguments addrp and realnump are mutually exclusive, we either use
addrp (for lval_memory), or use realnump (for lval_register).  This
can be done in a separate patch.

gdb:

2016-12-06  Yao Qi  <yao.qi@linaro.org>

	* frame.c (frame_register_unwind): Set *realnump if *lvalp is
	lval_register.
	* value.c (deprecated_value_next_frame_id_hack): Assert
	value->lval is lval_register.
	(deprecated_value_regnum_hack): Likewise.

diff --git a/gdb/frame.c b/gdb/frame.c
index 5414cb3..00001bc 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -1107,7 +1107,10 @@ frame_register_unwind (struct frame_info *frame, int regnum,
   *unavailablep = !value_entirely_available (value);
   *lvalp = VALUE_LVAL (value);
   *addrp = value_address (value);
-  *realnump = VALUE_REGNUM (value);
+  if (*lvalp == lval_register)
+    *realnump = VALUE_REGNUM (value);
+  else
+    *realnump = -1;
 
   if (bufferp)
     {
diff --git a/gdb/value.c b/gdb/value.c
index cc291cf..022900f 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1576,12 +1576,14 @@ deprecated_value_internalvar_hack (struct value *value)
 struct frame_id *
 deprecated_value_next_frame_id_hack (struct value *value)
 {
+  gdb_assert (value->lval == lval_register);
   return &value->location.reg.next_frame_id;
 }
 
 int *
 deprecated_value_regnum_hack (struct value *value)
 {
+  gdb_assert (value->lval == lval_register);
   return &value->location.reg.regnum;
 }