COMPAT_43 users?

[Brooks Davis]

On Wed, Aug 01, 2018 at 11:28:53AM -0400, Mark Johnston wrote:
> On Wed, Aug 01, 2018 at 10:55:12AM +0300, Konstantin Belousov wrote:
> > On Tue, Jul 31, 2018 at 05:49:20PM -0400, Mark Johnston wrote:
> > > The COMPAT_43 kernel option, which enables syscall support for 4.3BSD
> > > binaries, hasn't been enabled in the standard kernel configs for well
> > > over a decade, and doesn't appear to be a dependency of any other kernel
> > > features.  Nonetheless, the kernel contains quite a bit of code to
> > > support this option.  Does anyone use it in modern versions of FreeBSD
> > > or have any arguments for keeping it?
> > 
> > COMPAT_43 means two things, the third part is a.out image activator.
> > First thing is the lcall $7.$0 syscall emulator, both on amd64 and
> > (surprisingly) i386, after 4/4 split.  Second thing is the syscalls
> > compat shims.
> > 
> > Together, all three things allow to run pre-3.x binaries on the modern
> > machines, including amd64. I think this is useful at least for 'waving
> > the flag' about our ABI compatibility guarantees, and for the historic
> > software reconstruction. I run 1.1.8 chroot and several old binaries
> > sometimes, I know that bde does, and there was at least one more user
> > some time ago.
> > 
> > What do you mean by a lot of code ?  Syscall compats is relatively easy.
> > lcall $7,$0 emulation is very non-trivial but tiny.  I do maintain this
> > code and do not want it to go away.
> 
> Thanks, fair enough.  The question was prompted by seeing lots of
> COMPAT_OLDSOCK ifdefs while working on some socket code.

I've had to figure out the COMPAT_OLDSOCK stuff a couple times in the
last few years.  The way it's implementation is weird in that it seems
to change the system wide socket behavior in a few cases.  It might be
a worthy endeavor to refactor this into alternate entry points for an
a.out compat layer (it's also patently absurd that you can invoke (e.g.)
cpuset_setdomain(2) from an a.out binary).

-- Brooks
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