Re: RFC: selected frame in read_var_value

[Andrew Cagney <ac131313 at redhat dot com>]

> Thoughts on this?  I observed one case where the selected frame hadn't been
> initialized yet: when checking watchpoint values.  Oops!  The condition
> matches the case in which get_current_frame () can be reasonably expected to
> succeed.  There are a couple other places that need this same check, mostly
> functions which will work on globals as well as locals.

I think the caller, and not this code, should be the one deciding 
if/when a get_selected_frame should be called.  Otherwize the dependance 
on global state remains.

> An alternative would be to create a lifeless_frame and have
> get_current_frame return that when there is no running target; have it call
> error if a register is read, its base is requested, et cetera.  I suspect
> that would require some serious surgery.  We'd also need to pass
> lifeless_frame everywhere we could be passing a NULL frame now.  For
> instance, several callers of read_var_value will give it no frame.

Which exact case are you thinking of?  A core file should have a frame. 
 An exec file?  A lifeless frame (throw an error if any register is 
unwound) should be straight forward.

Andrew



> --- gdb-5.3.20030801/gdb/findvar.c.orig	2003-08-01 14:46:12.000000000 -0400
> +++ gdb-5.3.20030801/gdb/findvar.c	2003-08-01 14:50:27.000000000 -0400
> @@ -388,7 +388,7 @@ symbol_read_needs_frame (struct symbol *
>     and a stack frame id, read the value of the variable
>     and return a (pointer to a) struct value containing the value. 
>     If the variable cannot be found, return a zero pointer.
> -   If FRAME is NULL, use the deprecated_selected_frame.  */
> +   If FRAME is NULL, use the selected frame.  */
>  
>  struct value *
>  read_var_value (register struct symbol *var, struct frame_info *frame)
> @@ -404,8 +404,9 @@ read_var_value (register struct symbol *
>  
>    len = TYPE_LENGTH (type);
>  
> -  if (frame == NULL)
> -    frame = deprecated_selected_frame;
> +  if (frame == NULL && target_has_registers && target_has_stack
> +      && target_has_memory)
> +    frame = get_selected_frame ();