Re: [rfa?] Add frame_align(); Was: ARM stack alignment on hand called functions

[Keith Walker <keith.walker@arm.com>]

At 10:40 28/11/2002 +0000, Richard Earnshaw wrote:
> > Richard Earnshaw <rearnsha@arm.com> writes:
> >
> > |> > +/* Ensure that the ARM's stack pointer has the correct alignment 
> for a
> > |> > +   new frame.  */
> > |> > +static CORE_ADDR
> > |> > +arm_frame_align (struct gdbarch *gdbarch, CORE_ADDR addr)
> > |> > +{
> > |> > +  return (addr & -16);
> > |> > +}
> > |>
> > |> Yuck, two's complement assumption.
> >
> > No, -16 is implicitly cast to bfd_vma, which is unsigned, and this
> > operation is completely defined independent of the representation of
> > signed integers.
>
>Hmm, strictly speaking you are correct.  I don't have to like it though,
>and it means that the code is heavily dependent on the non-obvious fact
>that addr is an unsigned type to get the correct behaviour (if bfd_vma
>were to be changed to a signed type then this code would quietly break).
>
>So I'll change my comment to:
>
>Yuck, implicit cast of negative number to unsigned.

I notice that the h8300-tdep.c file defines some macros to do this sort of 
rounding ... round_up() and round_down().     As aligning addresses is a 
reasonable common thing to do maybe these macros should be moved to a more 
generic place and used whenever such rounding is required.    It doesn't 
fix the implicit cast issue, but would at least make finding where such 
alignment occurs easier.

Keith