Re: [PATCH] S/390 DWARF-2 CFI frame support

[Richard Henderson <rth@redhat.com>]

On Thu, Dec 04, 2003 at 09:09:12PM +0100, Ulrich Weigand wrote:
>   To fix this, I suggest the following.  What GCC assumes to happen
>   when it leaves a register unspecified in the CFI depends on whether
>   the register is call-saved or call-clobbered according to the 
>   target's ABI.  If it is call-saved (and unspecified), the function
>   doesn't save/restore it because it does not in fact ever modify it.
>   Thus, in this case the debugger should copy the value from the 
>   inner frame.  If it is call-clobbered (those will always be left
>   unspecified), it should be assumed undefined.

This is wrong.  The debugger should just assume *all* registers
that are not explicitly saved are preserved.  In the case of
call-clobbered registers, you just won't *know* that they are
actually dead.  But so what?  This is no worse than not having
location list information that tells you that a value is dead
after its register gets re-used for something else.

However, when I made this argument before, it wasn't good enough
for some people, and they added the annoying warning anyway.


r~