Re: unifdef MODULAR for powerpc

[Chuck Silvers <chuq%chuq.com@localhost>]

On Sun, Jun 28, 2020 at 06:45:21AM +1000, matthew green wrote:
> Rin Okuyama writes:
> > Hi,
> > 
> > There are a lot of ``#ifdef MODULAR'' in sys/arch/powerpc, in order to
> > provide ABI compatibility between oea/booke/ibm4xx kernels. However,
> > since 2011, we provide different kernel modules in /stand/modules for
> > the three architectures on evbppc. Therefore, I'd like to propose,
> > 
> > (1)  Unifdef MODULAR in sys/arch/powerpc.
> > (1') Expose {MIN,MAX}_PAGE_SIZE only for userland.
> > (2)  Provide kernel modules for three different archs also in /usr/tests.
> > 
> > Objections? And can you suggest any convenient method to realize (2)?
> > 
> > (a) How to build three different module binaries?
> > (b) How to select module binary in /usr/tests?
> > 
> > I will consider about it...
> 
> the multiple ABI modules were a workaround to enable the ability
> on all these platforms with the current issues in the platform
> code itself -- that a kernel can only run on one system.
> 
> the current state is really a workaround for the fact that the
> majority of the ABI is not stable across different cpu families
> inside powerpc.  long ago, x86 had problems with modules in
> DEBUG or LOCKDEBUG and sometimes DIAGNOSTIC kernels, but ad and
> others changed a lot of things such that the same module can work
> there, regardless of kernel build options.  ideally, this would
> also be true for xen, but we have the same workaround instead.
> 
> what this mostly means is making structures not change size or
> layout across due to build/cpu options, and avoiding using macros
> that expose these details.
> 
> i'm not objecting to (2) but i would much rather you worked on
> fixing this better.  for (1) be careful not to include dead code
> in !MODULAR kernels please.

I agree with the thought it would be much more useful to make the
powerpc kernel module ABI the same on all powerpc platforms so that
kernel modules can be shared between them, rather than further
entrenching the current sub-optimal state of affairs.

-Chuck