Re: Header symbols that shouldn't be visible to ports?

On Mon, Sep 05, 2022 at 08:41:58AM -0600, Alan Somers wrote:
> On Sat, Sep 3, 2022 at 11:10 PM Konstantin Belousov <kostikbel@gmail.com> wrote:
> >
> > On Sat, Sep 03, 2022 at 10:19:12AM -0600, Alan Somers wrote:
> > > Our /usr/include headers define a lot of symbols that are used by
> > > critical utilities in the base system like ps and ifconfig, but aren't
> > > stable across major releases.  Since they aren't stable, utilities
> > > built for older releases won't run correctly on newer ones.  Would it
> > > make sense to guard these symbols so they can't be used by programs in
> > > the ports tree?  There is some precedent for that, for example
> > > _WANT_SOCKET and _WANT_MNTOPTNAMES.
> > _WANT_SOCKET is clearly about exposing parts of the kernel definitions
> > for userspace code that wants to dig into kernel structures.  Similarly
> > for _WANT_MNTOPTNAMES, but in fact this thing is quite stable.  The
> > definitions are guarded by additional defines not due to their instability,
> > but because using them in userspace requires (much) more preparation from
> > userspace environment, which is either not trivial (_WANT_SOCKET) or
> > contradicts to standartized use of the header (_WANT_MNTOPTNAMES +
> > sys/mount.h).
> >
> > >
> > > I'm particular, I'm thinking about symbols like the following:
> > > MINCORE_SUPER
> > Why this symbol should be hidden?  It is implementation-defined and
> > intended to be exposed to userspace.  All MINCORE_* not only MINCORE_SUPER
> > are under BSD_VISIBLE braces, because POSIX does not define the symbols.
> 
> Because it isn't stable.  It changed for example in rev 847ab36bf22
> for 13.0.  Programs using the older value (including virtually every
> Rust program) won't work on 13.0 and later.

Why won't they work?  Code that tests (vec[i] & MINCORE_SUPER) using the
old value will still give the same result when running on a newer
kernel, since MINCORE_PSIND(1) is 0x20, the old MINCORE_SUPER value.
This isn't to say that the change was perfectly backwards compatible,
but I haven't seen an example of code which was broken by the change.