Re: Question on BIGGEST_ALIGNMENT in GCC on NetBSD/m68k
On Thu, 19 Jun 2025, Greg Ungerer wrote:
> On 19/6/25 08:29, Finn Thain wrote:
>
> > On Wed, 18 Jun 2025, Greg Ungerer wrote:
> >
> >>> It's not really necessary to enforce this on Coldfire. However,
> >>> since buildroot builds completely from source, it wouldn't even be a
> >>> problem to change the alignment there as well.
> >>
> >> Yes, that is totally right in my experience. Certainly in my ColdFire
> >> work it is pretty much always a build-everything approach via
> >> buildroot or similar. I wouldn't think an ABI change would actually
> >> worry too many ColdFire uses, they don't use distributions like
> >> debian on them. (I would love to hear from anyone who does!).
> >>
> >
> > That may work for end-users with a vendor BSP. But upstream developers
> > need to be able to swap components. In general, when debugging I often
> > have to run old binaries to find out whether I'm dealing with a deeper
> > regression or not. Also, there is the bisection problem. It's not just
> > a couple of distros who get to pay for an ABI break. It's the entire
> > ecosystem.
>
> I am sure there is value in that for some. Like I said though that has
> not been my experience with ColdFire. And by that I mean as the upstream
> maintainer of ColdFire Linux support for +20 years. I pretty mush
> _always_ build kernel + libs + user for testing even small kernel
> changes.
OK, so you're not building binutils, newlib, gcc, gdb etc. with each
revision. Do you use a board support package (BSP) from the vendor?
> My standard small system build takes less than 1 minute for everything.
> Again, I am just relating my experience with this - admittedly probably
> not typical of actual end users.
>
> FWIW even when I was working on shipping ColdFire based products my
> firmware was always a complete update, no separate kernel and user space
> updates. Typical of small embedded systems. I can't actually remember
> many times I have run with a previously compiled user space.
>
Given that on-chip RAM is scarce on Coldfire devices, it seems entirely
plausible that an alignment change could result in ENOMEM after a rebuild
-- unless the toolchain offered a choice of ABI.
So this becomes a burden for those who maintain tooling that deals with
ABIs, as well as for the vendor which has to support its BSP -- unless the
vendor also happens to desire a choice of alignment (that's why I raised
that question on 6/6).
Reply to: