On Mon, Sep 05, 2022 at 08:41:58AM -0600, Alan Somers wrote: > On Sat, Sep 3, 2022 at 11:10 PM Konstantin Belousov <kostik...@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.
