Saving to 32 bits of GPRs in signal context

[Steve Munroe]

Ulrich Weigand <Ulrich.Weigand at de.ibm.com> wrote on 05/29/2007 09:08:39 AM:

>
> Steve Munroe <sjmunroe at us.ibm.com> wrote on 05/29/2007 04:00:42 PM:
>
> > Yes exactly why make an incompatible ABI change to the powerp32 ABI,
when
> > you can just use the existing 64-bit ABI.
> >
> > Especially as you can only run what is proposed on 64-bit hardware!
> >
> > We don't need another ABI change to powerpc32 (still recovering from
the
> > -msecure-plt ABI change) and WE DONT NEED a 3rd ABI.
> >
> > ABI changes ripple everywhere (not just GCC/GLIBC) including all
debuggers
> > and performance tools. Believe me you really don't want this.
>
> Fully agreed.  This may have gotten lost in the discussion thread, but
what
> Ben originally proposed was *not* an ABI change, for exactly that reason.

> We simply want to allow strictly local use of 64-bit registers for
> performance optimization purposes, while still fully complying with
> the 32-bit ABI.
>

But unless you take the time to write it up like a full ABI change you are
never sure that it IS compatible. And any change to the size/shape of
ucontext_t is an ABI change.

Also if you want to debug this code (see long long variables correctly from
GDB or even see the upper 32-bits of GPRs) you will need an ABI change so
that GDB/DWARF knows what to do.


Steven J. Munroe
Linux on Power Toolchain Architect
IBM Corporation, Linux Technology Center