Re: git: b75062f23431 - main - riscv: Fix thread0.td_kstack_pages init

On Wed, Jan 18, 2023 at 04:53:51PM -0700, Warner Losh wrote:
> On Wed, Jan 18, 2023 at 3:07 PM Mitchell Horne <mhorne@freebsd.org> wrote:
> 
> >
> >
> > On 1/17/23 12:38, Brooks Davis wrote:
> > > The branch main has been updated by brooks:
> > >
> > > URL:
> > https://cgit.FreeBSD.org/src/commit/?id=b75062f23431fbabef1e7d665cae270b144f71b1
> > >
> > > commit b75062f23431fbabef1e7d665cae270b144f71b1
> > > Author:     Brooks Davis <brooks@FreeBSD.org>
> > > AuthorDate: 2023-01-17 16:36:15 +0000
> > > Commit:     Brooks Davis <brooks@FreeBSD.org>
> > > CommitDate: 2023-01-17 16:37:42 +0000
> > >
> > >      riscv: Fix thread0.td_kstack_pages init
> > >
> > >      Commit 0ef3ca7ae37c70e9dc83475dc2e68e98e1c2a418 initialized
> > >      thread0.td_kstack_pages to KSTACK_PAGES.  Due to the lack of an
> > >      include of opt_kstack_pages.h it used the fallback value of 4 from
> > >      machine/param.h.
> >
> > Does this mean that we could/should include opt_kstack_pages.h within
> > machine/param.h (under #ifdef _KERNEL)? This header is both a consumer
> > and provider of the KSTACK_PAGES definition, by virtue of the #ifndef. I
> > think the hidden dependency should be avoided, if possible.
> >
> 
> No. Including opt_XXXX.h is never OK in our .h files. They are used in too
> many places, some of which "cheat" and define _KERNEL becuse, well, they
> need to get to the kernel bits....  That will break...

We could potentially use the __has_include extension.  I don't think we
care about building the kernel with a compiler that isn't clang or gcc
and the usage pattern defined by gcc is safe for compilers that don't
define it.  We could do something like:

#ifdef _KERNEL
#ifndef KSTACK_PAGES
#ifdef __has_include
#if __has_include("opt_kstack_pages.h")
#include "opt_kstack_pages.h"
#endif
#endif
#endif
#endif
<old #ifndef KSTACK_PAGES code>

> 
> I do agree, however, that the current interface is less than ideal...
> 
> 
> > Of course, the problem at hand has been fixed and we want to keep direct
> > consumers of KSTACK_PAGES to a minimum, but I think the point still stands.
> >
> 
> I think it's a good point, but the current way is likely the least-bad way
> to accomplish things.
> 
> It would be much better if we could remove it from machine/param.h and
> opt_XXX.h always defines it, even the default value when it's not otherwise
> specified. However, we don't (currently) have a way to set default values
> in config(8). We could add it, since the efforts at config++ have thus far
> fallen flat....

I think this is probably the better direction to move.  There aren't any
in-tree uses of KSTACK_PAGES so removing the definition should be fine.

-- Brooks